SOME ASPECTS OF MAN-MADE CLIMATE MODIFICATION AND DESERTIFICATION

by

HERMANN FLOHN

Institute of Meteorology University of Bonn

Energetics of the climatic system

A series of climatic anomalies from about 1968 onwards with serious consequences on human welfare and economy has brought the problem of man-made or man-triggered climatic variability to general attention For the time being we ought perhaps to avoid the term climatic change which should be restricted to major changes (as between an ice-age and a warm interglacial period) though this is a matter of definition and of the time-scale under consideration Rather we prefer the term climatic flucshytuation for short lived (eg interannual) deviations and the term climatic variation for such changes as have been observed using 3o-year averages since the beginning of instrumental observations - that is since AD 1650

Recent model simulations have led to a growing consensus that our climate cannot be regarded as stationary Studies in climatic history (Nashytional Academy of Sciences 1975 WMO-JCSU Joint Organizing Comshymittee 1975) have revealed the fact that quite abrupt natural changes occurred between ice-ages and warm interglacial periods Evidence has been found that the transition between two quite different climatic patshyterns may last no more than a century or even less

It is thus obvious that the 30o-year period of instrumental observations - records were first made by the Florentine Academy and by the Royal Society of London beginning around 1650 - is much too short to show all possible excesses of climate Consequently it is necessary to extend the records into much longer time-scales by using (and quantifying) proxy data - such as weather diaries kept without instruments observations of ice (especially sea-ice) and snow tree-rings lake levels pollen profiles from bogs sea-bottom and ice cores with annual layering or radioactive chronoshy

Some Aspects of Man-Made Climate Modification and Desertification 4S

logy (C14) The Icelandic Annals are among the most valuable of these sources (Bergthorsson 1969)

How far is mans increasing activity responsible (SMIC Report 1971) for recent climatic vagaries Has he inadvertently interfered with the highly interactive climatic system (Schnelder 1975 WMO-JCSU Joint Organizing Committee 1975) whim consists of atmosphere ocean ice and snow and soil and the biosphere (Fig I) A large-scale Global Atmoshyspheric Researm Programme (GARP) was organized at first only for the purpose of extending the predictability of the weather and perhaps helping to answer these questions but it soon was expanded to provide a deeper insight into the physical basis of climate and into the multitude of nonshylinear feedback memanisms within the climatic system and its subsystems

In recent years impressive work has been done in designing physicoshymathematical models of large-scale atmospheric circulation and of climate

ClI MATIC SYSTEM (with interactions)

km mblhPa 50~---------------------------------~~--~0

~S~tr~a~t~o~SPjh~e~re~10~O~-_5~0~o~d~~~~~~~~~_______~200I- P M H M TROPOPAUSE

_____~__~~~~~loOO -60 DC

barll0SPa

4-sd

1~~~~________~R~E~~H~~M~~P

~~~--------------~--~~~o

THERMOCLINI Groundwater

10-104yearsL-__-- 100

~------------~amp--~-i40I I I I I

Runoff

Deep Ocean 1500 years ITw

bullI I

deg 37 +20C 000

Weak Interact ion R = Radiation M=Momentum

Strong bull H =Heat P= Particles Gases ~ Very Strong bull E = Evaporat ion

Figure I - Climatic System with characteristic time-scales and interactions

Hermann Flohn

but many physical interactions within the system are still imperfecdy understood (JMO-JCSU Joint Organizing Committee 1975) The results of these computations should therefore only be considered as sensitivity tests of as yet incomplete models not as simulations of the real climate

In this article it is intended to look mainly at the contribution of atmoshyspheric and oceanic processes to climatic variability together with some consideration of the role of land-use conversion However owing to the many interactions some overlapping hardly can be avoided

Energetics of natural and man-made climatic processes

A truly realistic simulation of climatic variations is at present impossible (and will probably remain so for years to come) Thus we must restrict ourselves to a comparison of natural phenomena - such as volcanic erupshytions or possible variations in solar radiation - with man-made effects (Fig 2) only by estimating their energy contribution to the climatic system As the climatic system is driven not by the whole of solar radiation but merely by its regional (e g latitudinal) differences only a small fraction of it is used in the weather (and climate) producing processes (Flohn 1973 a) These latter processes are the production of available potential energy of the pressure and temperature distribution and - equal to that shythe final dissipation of the kinetic energy of the wind by friction (see Table 1)

Using this value as a reference we can estimate the energy contribution of some factors which are assumed to cause short-period climatic fluc-

CAUSES OF GLOBAL CLIMATIC FLUCTUATIONS

Natural causes Man-made causes

External b Solar constant Carbon dioxide (C02)

Orbital changes (104_10) Fossil energy Volcanic dust Nuclear energy

Internal b Arctic sea-ice Tropospheric dust b Antarctic sea-ice (incl man-triggered dust) b Air-sea interaction Conversion of vegetation (102-1(1) Antarctic surges (gt 1~) (land-use desertification)

Impact on hydrological cycle (irrigation reservoirs)

( ) =probable time-scale (In years) b = Time variation of

Figure 1 - Causes of global climatic fluctuations External and internal refer to the climatic system

47 Some Aspects of Man-Made Qimate Modification and Desertification

Table I - Natural climatic energy parameters

A) Solar constant - Net radiation Earths surface Production of avail POt energy Geothermal heat

B) Photosynthetic processes Large-scale volcanic eroption Change of cloudiness (1 00) Change of oceanic evaporation (Equat Pacific) Change of snow-cover (u 00) Change of arctic sea-ice (~O ) Large magnetic storms

Global scale Terawatts (1012 W) Wm f

173000 340 pooo 10~

1200 ~middot4

Jl 0063

104 160 0middot3

350 067

-300 lIO

100 lOO-~ooTW shy

tuations (Table 1 B) We consider first - disregarding some recent controshyversies - the stratospheric dust-veil after very large volcanic eruptions such as that of Krakatoa in 1883 a world-wide cooling effect lasts a few years with a maximum near 1 degC in the first year equivalent to an energyshyloss of about 160 Terawatt (TW) Average cloudiness can change by I-Z deg0 without being detected by surface observers or satellites evaporashytion above the equatorial Pacific can be substantially increased by ceasing upwelling during an El Nifio episode (as in 1972) satellite-observed snowshycover can vary from year to year by about I2 deg0 the extension of the arctic sea-ice has varied by about zo Ofo during the last millennium

All these internal changes within the climatic system contribute (see TableI B) an energy input or loss of between about 100 and 300 TW (WMO-JCSU Joint Organizing Committee 1975) equivalent to global temperature variations of 06-20 degC such values are typical of minor flucshytuations of climate such as have been experienced during the last few centuries They are also typical of the (still uncertain) fluctuations caused by solar events through modulations of the magnetosphere

Such events are the natural background against which we may judge the role of anthropogenic effects (see Table z) (SMIC Report 1971 Bach 1976) By far the largest effect is that of agricultural irrigation (Lvovich 1969 Flohn 1973 a) which spans more than 21 X 106 kmtj here the area of the reservoirs should be added - unfortunately there do not exist any statistics for the small ponds but the larger ones cover about 04 X 106 km

Hermann Flohn

If we estimate the total area at 25 X 1041 km and the additional evaposhytranspiration from both at I mllannum - this is a conservative figure in arid and semiarid areas - we come to an annual water loss of 2500 kms

(Lvovich [1969] gives a figure of 1700 kms budor 1965) or the equivalent of about ISO TW

The direct input of heat due to consumption of fossil and nuclear fuels is at present equivalent to 8 TW (FSIC Report 1971 FIohn 1973a) This input consists not only of sensible heat into which most other energy forms are finally converted an increasing part of it consists of latent heat (evashyporation from cooling towers etc) and a small part of chemical energy of compounds and of potential energy (e g in tall buildings) Owing to the increasing concentration of population industry and traffic (altoshygether less than 500000 km) the greater portion of it is released in high concentrations (see Table 3) which are not negligible when compared with the natural net radiation i e the balance between incoming and outshygoing radiation at the earths surface both in visible and infra-red parts of the spectrum (global average - 100 Wm2 central and western Europe 50-70 W 1m2

)

A typical energy consumption density in large cities and industrial censhytres is 10-20 Wm2 whim is valid above areas of 100-1000 kmll and in some cases (Table 3) even up to 10000 km2 whim is still far below the synoptic scale (-- 106 km) Thus direct heat input affects mainly the local scale (Landsberg 1970) producing permanent urban heat-islands and under unstable conditions increasing convective activity This is also true of intense-point heat sources sum as power-station parks cooling towers or local fires In sum cases the heat input can ream 106 (Hamburg bombing fire 24 July 1943 6 hrs above 13 km) or even 106 W1m2 (cooling tower surface 700 mll) with a substantial injection of water vapour

While this heat is included as a small but locally significant amount

Table ~ - Antbropogenic climatic energy parameters

Terawatts (I01I W)

Large-scale irrigation reservoirs 150

Heat input by energy consumption 8

Annual increase of COt 16

Tropospheric dust 6

Savannah bush-fires etc 3

world-wide 15-z0 mosdy northern

hemisphere 10 X loftkmt

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Some Aspects of Man-Made Climate Modification and Desertification 4S

logy (C14) The Icelandic Annals are among the most valuable of these sources (Bergthorsson 1969)

How far is mans increasing activity responsible (SMIC Report 1971) for recent climatic vagaries Has he inadvertently interfered with the highly interactive climatic system (Schnelder 1975 WMO-JCSU Joint Organizing Committee 1975) whim consists of atmosphere ocean ice and snow and soil and the biosphere (Fig I) A large-scale Global Atmoshyspheric Researm Programme (GARP) was organized at first only for the purpose of extending the predictability of the weather and perhaps helping to answer these questions but it soon was expanded to provide a deeper insight into the physical basis of climate and into the multitude of nonshylinear feedback memanisms within the climatic system and its subsystems

In recent years impressive work has been done in designing physicoshymathematical models of large-scale atmospheric circulation and of climate

ClI MATIC SYSTEM (with interactions)

km mblhPa 50~---------------------------------~~--~0

~S~tr~a~t~o~SPjh~e~re~10~O~-_5~0~o~d~~~~~~~~~_______~200I- P M H M TROPOPAUSE

_____~__~~~~~loOO -60 DC

barll0SPa

4-sd

1~~~~________~R~E~~H~~M~~P

~~~--------------~--~~~o

THERMOCLINI Groundwater

10-104yearsL-__-- 100

~------------~amp--~-i40I I I I I

Runoff

Deep Ocean 1500 years ITw

bullI I

deg 37 +20C 000

Weak Interact ion R = Radiation M=Momentum

Strong bull H =Heat P= Particles Gases ~ Very Strong bull E = Evaporat ion

Figure I - Climatic System with characteristic time-scales and interactions

Hermann Flohn

but many physical interactions within the system are still imperfecdy understood (JMO-JCSU Joint Organizing Committee 1975) The results of these computations should therefore only be considered as sensitivity tests of as yet incomplete models not as simulations of the real climate

In this article it is intended to look mainly at the contribution of atmoshyspheric and oceanic processes to climatic variability together with some consideration of the role of land-use conversion However owing to the many interactions some overlapping hardly can be avoided

Energetics of natural and man-made climatic processes

A truly realistic simulation of climatic variations is at present impossible (and will probably remain so for years to come) Thus we must restrict ourselves to a comparison of natural phenomena - such as volcanic erupshytions or possible variations in solar radiation - with man-made effects (Fig 2) only by estimating their energy contribution to the climatic system As the climatic system is driven not by the whole of solar radiation but merely by its regional (e g latitudinal) differences only a small fraction of it is used in the weather (and climate) producing processes (Flohn 1973 a) These latter processes are the production of available potential energy of the pressure and temperature distribution and - equal to that shythe final dissipation of the kinetic energy of the wind by friction (see Table 1)

Using this value as a reference we can estimate the energy contribution of some factors which are assumed to cause short-period climatic fluc-

CAUSES OF GLOBAL CLIMATIC FLUCTUATIONS

Natural causes Man-made causes

External b Solar constant Carbon dioxide (C02)

Orbital changes (104_10) Fossil energy Volcanic dust Nuclear energy

Internal b Arctic sea-ice Tropospheric dust b Antarctic sea-ice (incl man-triggered dust) b Air-sea interaction Conversion of vegetation (102-1(1) Antarctic surges (gt 1~) (land-use desertification)

Impact on hydrological cycle (irrigation reservoirs)

( ) =probable time-scale (In years) b = Time variation of

Figure 1 - Causes of global climatic fluctuations External and internal refer to the climatic system

47 Some Aspects of Man-Made Qimate Modification and Desertification

Table I - Natural climatic energy parameters

A) Solar constant - Net radiation Earths surface Production of avail POt energy Geothermal heat

B) Photosynthetic processes Large-scale volcanic eroption Change of cloudiness (1 00) Change of oceanic evaporation (Equat Pacific) Change of snow-cover (u 00) Change of arctic sea-ice (~O ) Large magnetic storms

Global scale Terawatts (1012 W) Wm f

173000 340 pooo 10~

1200 ~middot4

Jl 0063

104 160 0middot3

350 067

-300 lIO

100 lOO-~ooTW shy

tuations (Table 1 B) We consider first - disregarding some recent controshyversies - the stratospheric dust-veil after very large volcanic eruptions such as that of Krakatoa in 1883 a world-wide cooling effect lasts a few years with a maximum near 1 degC in the first year equivalent to an energyshyloss of about 160 Terawatt (TW) Average cloudiness can change by I-Z deg0 without being detected by surface observers or satellites evaporashytion above the equatorial Pacific can be substantially increased by ceasing upwelling during an El Nifio episode (as in 1972) satellite-observed snowshycover can vary from year to year by about I2 deg0 the extension of the arctic sea-ice has varied by about zo Ofo during the last millennium

All these internal changes within the climatic system contribute (see TableI B) an energy input or loss of between about 100 and 300 TW (WMO-JCSU Joint Organizing Committee 1975) equivalent to global temperature variations of 06-20 degC such values are typical of minor flucshytuations of climate such as have been experienced during the last few centuries They are also typical of the (still uncertain) fluctuations caused by solar events through modulations of the magnetosphere

Such events are the natural background against which we may judge the role of anthropogenic effects (see Table z) (SMIC Report 1971 Bach 1976) By far the largest effect is that of agricultural irrigation (Lvovich 1969 Flohn 1973 a) which spans more than 21 X 106 kmtj here the area of the reservoirs should be added - unfortunately there do not exist any statistics for the small ponds but the larger ones cover about 04 X 106 km

Hermann Flohn

If we estimate the total area at 25 X 1041 km and the additional evaposhytranspiration from both at I mllannum - this is a conservative figure in arid and semiarid areas - we come to an annual water loss of 2500 kms

(Lvovich [1969] gives a figure of 1700 kms budor 1965) or the equivalent of about ISO TW

The direct input of heat due to consumption of fossil and nuclear fuels is at present equivalent to 8 TW (FSIC Report 1971 FIohn 1973a) This input consists not only of sensible heat into which most other energy forms are finally converted an increasing part of it consists of latent heat (evashyporation from cooling towers etc) and a small part of chemical energy of compounds and of potential energy (e g in tall buildings) Owing to the increasing concentration of population industry and traffic (altoshygether less than 500000 km) the greater portion of it is released in high concentrations (see Table 3) which are not negligible when compared with the natural net radiation i e the balance between incoming and outshygoing radiation at the earths surface both in visible and infra-red parts of the spectrum (global average - 100 Wm2 central and western Europe 50-70 W 1m2

)

A typical energy consumption density in large cities and industrial censhytres is 10-20 Wm2 whim is valid above areas of 100-1000 kmll and in some cases (Table 3) even up to 10000 km2 whim is still far below the synoptic scale (-- 106 km) Thus direct heat input affects mainly the local scale (Landsberg 1970) producing permanent urban heat-islands and under unstable conditions increasing convective activity This is also true of intense-point heat sources sum as power-station parks cooling towers or local fires In sum cases the heat input can ream 106 (Hamburg bombing fire 24 July 1943 6 hrs above 13 km) or even 106 W1m2 (cooling tower surface 700 mll) with a substantial injection of water vapour

While this heat is included as a small but locally significant amount

Table ~ - Antbropogenic climatic energy parameters

Terawatts (I01I W)

Large-scale irrigation reservoirs 150

Heat input by energy consumption 8

Annual increase of COt 16

Tropospheric dust 6

Savannah bush-fires etc 3

world-wide 15-z0 mosdy northern

hemisphere 10 X loftkmt

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Hermann Flohn

but many physical interactions within the system are still imperfecdy understood (JMO-JCSU Joint Organizing Committee 1975) The results of these computations should therefore only be considered as sensitivity tests of as yet incomplete models not as simulations of the real climate

In this article it is intended to look mainly at the contribution of atmoshyspheric and oceanic processes to climatic variability together with some consideration of the role of land-use conversion However owing to the many interactions some overlapping hardly can be avoided

Energetics of natural and man-made climatic processes

A truly realistic simulation of climatic variations is at present impossible (and will probably remain so for years to come) Thus we must restrict ourselves to a comparison of natural phenomena - such as volcanic erupshytions or possible variations in solar radiation - with man-made effects (Fig 2) only by estimating their energy contribution to the climatic system As the climatic system is driven not by the whole of solar radiation but merely by its regional (e g latitudinal) differences only a small fraction of it is used in the weather (and climate) producing processes (Flohn 1973 a) These latter processes are the production of available potential energy of the pressure and temperature distribution and - equal to that shythe final dissipation of the kinetic energy of the wind by friction (see Table 1)

Using this value as a reference we can estimate the energy contribution of some factors which are assumed to cause short-period climatic fluc-

CAUSES OF GLOBAL CLIMATIC FLUCTUATIONS

Natural causes Man-made causes

External b Solar constant Carbon dioxide (C02)

Orbital changes (104_10) Fossil energy Volcanic dust Nuclear energy

Internal b Arctic sea-ice Tropospheric dust b Antarctic sea-ice (incl man-triggered dust) b Air-sea interaction Conversion of vegetation (102-1(1) Antarctic surges (gt 1~) (land-use desertification)

Impact on hydrological cycle (irrigation reservoirs)

( ) =probable time-scale (In years) b = Time variation of

Figure 1 - Causes of global climatic fluctuations External and internal refer to the climatic system

47 Some Aspects of Man-Made Qimate Modification and Desertification

Table I - Natural climatic energy parameters

A) Solar constant - Net radiation Earths surface Production of avail POt energy Geothermal heat

B) Photosynthetic processes Large-scale volcanic eroption Change of cloudiness (1 00) Change of oceanic evaporation (Equat Pacific) Change of snow-cover (u 00) Change of arctic sea-ice (~O ) Large magnetic storms

Global scale Terawatts (1012 W) Wm f

173000 340 pooo 10~

1200 ~middot4

Jl 0063

104 160 0middot3

350 067

-300 lIO

100 lOO-~ooTW shy

tuations (Table 1 B) We consider first - disregarding some recent controshyversies - the stratospheric dust-veil after very large volcanic eruptions such as that of Krakatoa in 1883 a world-wide cooling effect lasts a few years with a maximum near 1 degC in the first year equivalent to an energyshyloss of about 160 Terawatt (TW) Average cloudiness can change by I-Z deg0 without being detected by surface observers or satellites evaporashytion above the equatorial Pacific can be substantially increased by ceasing upwelling during an El Nifio episode (as in 1972) satellite-observed snowshycover can vary from year to year by about I2 deg0 the extension of the arctic sea-ice has varied by about zo Ofo during the last millennium

All these internal changes within the climatic system contribute (see TableI B) an energy input or loss of between about 100 and 300 TW (WMO-JCSU Joint Organizing Committee 1975) equivalent to global temperature variations of 06-20 degC such values are typical of minor flucshytuations of climate such as have been experienced during the last few centuries They are also typical of the (still uncertain) fluctuations caused by solar events through modulations of the magnetosphere

Such events are the natural background against which we may judge the role of anthropogenic effects (see Table z) (SMIC Report 1971 Bach 1976) By far the largest effect is that of agricultural irrigation (Lvovich 1969 Flohn 1973 a) which spans more than 21 X 106 kmtj here the area of the reservoirs should be added - unfortunately there do not exist any statistics for the small ponds but the larger ones cover about 04 X 106 km

Hermann Flohn

If we estimate the total area at 25 X 1041 km and the additional evaposhytranspiration from both at I mllannum - this is a conservative figure in arid and semiarid areas - we come to an annual water loss of 2500 kms

(Lvovich [1969] gives a figure of 1700 kms budor 1965) or the equivalent of about ISO TW

The direct input of heat due to consumption of fossil and nuclear fuels is at present equivalent to 8 TW (FSIC Report 1971 FIohn 1973a) This input consists not only of sensible heat into which most other energy forms are finally converted an increasing part of it consists of latent heat (evashyporation from cooling towers etc) and a small part of chemical energy of compounds and of potential energy (e g in tall buildings) Owing to the increasing concentration of population industry and traffic (altoshygether less than 500000 km) the greater portion of it is released in high concentrations (see Table 3) which are not negligible when compared with the natural net radiation i e the balance between incoming and outshygoing radiation at the earths surface both in visible and infra-red parts of the spectrum (global average - 100 Wm2 central and western Europe 50-70 W 1m2

)

A typical energy consumption density in large cities and industrial censhytres is 10-20 Wm2 whim is valid above areas of 100-1000 kmll and in some cases (Table 3) even up to 10000 km2 whim is still far below the synoptic scale (-- 106 km) Thus direct heat input affects mainly the local scale (Landsberg 1970) producing permanent urban heat-islands and under unstable conditions increasing convective activity This is also true of intense-point heat sources sum as power-station parks cooling towers or local fires In sum cases the heat input can ream 106 (Hamburg bombing fire 24 July 1943 6 hrs above 13 km) or even 106 W1m2 (cooling tower surface 700 mll) with a substantial injection of water vapour

While this heat is included as a small but locally significant amount

Table ~ - Antbropogenic climatic energy parameters

Terawatts (I01I W)

Large-scale irrigation reservoirs 150

Heat input by energy consumption 8

Annual increase of COt 16

Tropospheric dust 6

Savannah bush-fires etc 3

world-wide 15-z0 mosdy northern

hemisphere 10 X loftkmt

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

47 Some Aspects of Man-Made Qimate Modification and Desertification

Table I - Natural climatic energy parameters

A) Solar constant - Net radiation Earths surface Production of avail POt energy Geothermal heat

B) Photosynthetic processes Large-scale volcanic eroption Change of cloudiness (1 00) Change of oceanic evaporation (Equat Pacific) Change of snow-cover (u 00) Change of arctic sea-ice (~O ) Large magnetic storms

Global scale Terawatts (1012 W) Wm f

173000 340 pooo 10~

1200 ~middot4

Jl 0063

104 160 0middot3

350 067

-300 lIO

100 lOO-~ooTW shy

tuations (Table 1 B) We consider first - disregarding some recent controshyversies - the stratospheric dust-veil after very large volcanic eruptions such as that of Krakatoa in 1883 a world-wide cooling effect lasts a few years with a maximum near 1 degC in the first year equivalent to an energyshyloss of about 160 Terawatt (TW) Average cloudiness can change by I-Z deg0 without being detected by surface observers or satellites evaporashytion above the equatorial Pacific can be substantially increased by ceasing upwelling during an El Nifio episode (as in 1972) satellite-observed snowshycover can vary from year to year by about I2 deg0 the extension of the arctic sea-ice has varied by about zo Ofo during the last millennium

All these internal changes within the climatic system contribute (see TableI B) an energy input or loss of between about 100 and 300 TW (WMO-JCSU Joint Organizing Committee 1975) equivalent to global temperature variations of 06-20 degC such values are typical of minor flucshytuations of climate such as have been experienced during the last few centuries They are also typical of the (still uncertain) fluctuations caused by solar events through modulations of the magnetosphere

Such events are the natural background against which we may judge the role of anthropogenic effects (see Table z) (SMIC Report 1971 Bach 1976) By far the largest effect is that of agricultural irrigation (Lvovich 1969 Flohn 1973 a) which spans more than 21 X 106 kmtj here the area of the reservoirs should be added - unfortunately there do not exist any statistics for the small ponds but the larger ones cover about 04 X 106 km

Hermann Flohn

If we estimate the total area at 25 X 1041 km and the additional evaposhytranspiration from both at I mllannum - this is a conservative figure in arid and semiarid areas - we come to an annual water loss of 2500 kms

(Lvovich [1969] gives a figure of 1700 kms budor 1965) or the equivalent of about ISO TW

The direct input of heat due to consumption of fossil and nuclear fuels is at present equivalent to 8 TW (FSIC Report 1971 FIohn 1973a) This input consists not only of sensible heat into which most other energy forms are finally converted an increasing part of it consists of latent heat (evashyporation from cooling towers etc) and a small part of chemical energy of compounds and of potential energy (e g in tall buildings) Owing to the increasing concentration of population industry and traffic (altoshygether less than 500000 km) the greater portion of it is released in high concentrations (see Table 3) which are not negligible when compared with the natural net radiation i e the balance between incoming and outshygoing radiation at the earths surface both in visible and infra-red parts of the spectrum (global average - 100 Wm2 central and western Europe 50-70 W 1m2

)

A typical energy consumption density in large cities and industrial censhytres is 10-20 Wm2 whim is valid above areas of 100-1000 kmll and in some cases (Table 3) even up to 10000 km2 whim is still far below the synoptic scale (-- 106 km) Thus direct heat input affects mainly the local scale (Landsberg 1970) producing permanent urban heat-islands and under unstable conditions increasing convective activity This is also true of intense-point heat sources sum as power-station parks cooling towers or local fires In sum cases the heat input can ream 106 (Hamburg bombing fire 24 July 1943 6 hrs above 13 km) or even 106 W1m2 (cooling tower surface 700 mll) with a substantial injection of water vapour

While this heat is included as a small but locally significant amount

Table ~ - Antbropogenic climatic energy parameters

Terawatts (I01I W)

Large-scale irrigation reservoirs 150

Heat input by energy consumption 8

Annual increase of COt 16

Tropospheric dust 6

Savannah bush-fires etc 3

world-wide 15-z0 mosdy northern

hemisphere 10 X loftkmt

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Hermann Flohn

If we estimate the total area at 25 X 1041 km and the additional evaposhytranspiration from both at I mllannum - this is a conservative figure in arid and semiarid areas - we come to an annual water loss of 2500 kms

(Lvovich [1969] gives a figure of 1700 kms budor 1965) or the equivalent of about ISO TW

The direct input of heat due to consumption of fossil and nuclear fuels is at present equivalent to 8 TW (FSIC Report 1971 FIohn 1973a) This input consists not only of sensible heat into which most other energy forms are finally converted an increasing part of it consists of latent heat (evashyporation from cooling towers etc) and a small part of chemical energy of compounds and of potential energy (e g in tall buildings) Owing to the increasing concentration of population industry and traffic (altoshygether less than 500000 km) the greater portion of it is released in high concentrations (see Table 3) which are not negligible when compared with the natural net radiation i e the balance between incoming and outshygoing radiation at the earths surface both in visible and infra-red parts of the spectrum (global average - 100 Wm2 central and western Europe 50-70 W 1m2

)

A typical energy consumption density in large cities and industrial censhytres is 10-20 Wm2 whim is valid above areas of 100-1000 kmll and in some cases (Table 3) even up to 10000 km2 whim is still far below the synoptic scale (-- 106 km) Thus direct heat input affects mainly the local scale (Landsberg 1970) producing permanent urban heat-islands and under unstable conditions increasing convective activity This is also true of intense-point heat sources sum as power-station parks cooling towers or local fires In sum cases the heat input can ream 106 (Hamburg bombing fire 24 July 1943 6 hrs above 13 km) or even 106 W1m2 (cooling tower surface 700 mll) with a substantial injection of water vapour

While this heat is included as a small but locally significant amount

Table ~ - Antbropogenic climatic energy parameters

Terawatts (I01I W)

Large-scale irrigation reservoirs 150

Heat input by energy consumption 8

Annual increase of COt 16

Tropospheric dust 6

Savannah bush-fires etc 3

world-wide 15-z0 mosdy northern

hemisphere 10 X loftkmt

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Some Aspects of Man-Made Climate Modification and Desertification 49

in the global atmospheric heat budget near the surface the role of CO2

(Bolin 1975 WMLO-JCSU Joint Organizing Committee 1975) emanating I from fossil fuels is different Here absorption of terrestrial radiation in the Il-15 pm range leads to higher temperatures in the troposphere (and inshyeffectively lower temperatures in the stratosphere) This radiational warmshying is difficult to assess because of its possible interaction with water vapour and its combination with dynamic processes Taking these proshycesses into account a doubling of the CO2 content alone should lead to a global warming of + 19degC (Manabe amp Wetherald 1975) CO2 concenshytration increased from about 190 ppm before massive industrialization (1880) to 327 ppm (+ 13 Ofo) as the most recent value (1975) this would have yielded a global warming of nearly + 04 degC equivalent to about 60 TW Owing to the inadequacies of the network of climatological stashytions especially to the lack of long homogeneous series above large oceans and polar areas this value is not yet distinguishable as an entity Local CO2

values up to 30 ppm higher have been observed but because of a residence time of nearly 6 years the global distribution of CO2 is - if seasonal variashytions are neglected - fairly uniform An increase of I ppm (I-l ppm anshynually in recent years) yields an energy input of 16 TW

Recent investigations (Wang et aI 1976) have indicated that the greenshyhouse effect of CO2 is further enhanced by other man-made trace-gases such as the halocarbons (freons with an atmospheric residence time of 40-70 years) N 20 (from fertilizers) CHi and NHs Even if the further use of freons is prohibited the combined warming effect of these gases will nevertheless reach about 50 Ofo of the CO2 effect if it cannot be proshyhibited the combined effect may even double that of CO2 alone On account of the long residence time of these inrared-absorbing gases and their fairly rapid mixing they will soon take the leadership in the anthroshypogenic impacts on climate on a global scale

The role of tropospheric dust has been frequently investigated with regard only to scattering (disregarding absorption) the result of which is atmospheric cooling However this result is inconsistent with the facts which indicate that nocturnal and average temperatures not only in indushystrial areas but also in dust-laden arid areas are significantly higher than in others More recent models including realistic absorption coefficients corshyrectly result in warming - at least in areas with high or normal surface albedo The essential quantity is the ratio between the particle absorption and its backscatter as the bulk of the aerosol particles are produced above land where the surface albedo is higher than above sea their warming effect predominates Our estimate is based on the warming of a local or regional low-level dust layer (below 850 mb) The role of man-made vegeshy

4 Applied Sciences

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Hermann Flohn

Table 3 - Energy consumption (EC) at local and regional scales

Area ECDensity Pop Density EC Intensity kro2 Wm2 caplkm2 KWcap

New York Manhattan 59 63 0 19000 lIO

Moscow 878 u7 73 00 168 Osaka-Kobe 741 56 5800 9middot7 West Berlin (building area) 134 11 9900 11

Industrial Area NW Germany 103 X 103 101 1100 8middot9 Boswash Megalopolis USA 87 X Icl 4middot4 380 111 Donez Basin USSR 53 X 103 14 145 9middot3 Japan 366 X 103 07 1 170 1middot7 14 eastern states USA 930 X 103 III 97 Il6 Central + Western Europe 1433 X 103 0middot77 170 4-5

Africa South America 48 X 10deg 0004 II 04

tation fires especially in the tropical savannas should not be neglected even if the estimates (Table z) are uncertain

The result of all these estimates converges to a slight but general warmshying each effect contributing essentially in the same direction It should be mentioned however that the energy comparisons in Tables I and z are not quite compatible at least regarding the efficiency time While sensible heat (and latent heat after precipitation) has a residence time of only I -z days due to infra-red cooling the residence time and thus the efficiency of CO2 and of the halocarbons is of the order of 6 respectively 50 years i e 103-10 as much as that of heat (enthalpy)

It should be mentioned that R A Bryson (1974 1975) still maintains a hypothesis of a predominating cooling caused by tropospheric dust (with its residence time of z-zo days) But most climatologists now agree to a hypothesis of increasing predominance of warming and they give parshyticular attention to the future role of CO2 and other infra-red absorbing gases

There is no question that the impact of man on the climatic system has now reached a level near to that of natural climatic fluctuations and that we are on the fringe of anthropogenic climatic fluctuations on a global or at least a hemispheric scale

Human impacts on the global water-budget

Even more effective are the man-made changes in the hydrological cycle of precipitation evaporation and runoff According to the most reliable

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

51 Some Aspects of Man-Made Climate Modification and Desertification

estimates (Baumgartner amp Reichel 1975) the global amount of evaporashytion (E) and precipitation (P) is 496 X lOs km8annum equivalent to 973 mmlannum E needs 16 Wm2 or about 15 Ofo of the net radiation at the surface On the continents PL yields 1II X lOS km3 and EL 11 X 108 kms while runoff R with 40 X lOS kms closes the budget According to Lvoshyvichs estimate valid for 1965 man uses about 2850 km3 or 1 deg0 of R from which 1800 km3 is added to ELbull These figures (Flohn 1913 a) must be upgraded over the last 10 years by 20-30 Ofo thus an estimated increase of EL by 1500 km3 (= 35 Ofo) is not unrealistic On a global scale these figures involve a redistribution only of EL similar figures for PL cannot be given

This increase of EL mainly for irrigation is a fairly recent developshyment following a slow reduction through many centuries Since neolithic times 4000 (or more) years ago man has been incessantly destroying (SMIC Report 1911) the natural vegetation of grasslands (by overgrazing) dry forests (by buming) and humid forests (by shifting cultivation) with the result that EL has been substantially diminished In mid-latitude forests the ratio EP changes after deforestation from 52 Ofo to 41 Ofo this loss of EL by about 20 Ofo can be taken as a conservative minimum for tropical rain-forests (Amazon) Then more energy is available for direct heating of the air (sensible heat) deforestation means local warming in contrast to local cooling after irrigation Large-scale irrigation - e g the Punjab with 85000 km2 using an energy amount near to 13 TW for EL - may thus also to a certain degree alter the regional climate provided that irrishygated areas lie close together and are not interspersed with arid land An increase of EL by 1500 km3 would need 150 TW of heat energy which is no longer available as sensible heat This is apparently above the critical threshold of natural climatic fluctuations but owing to the wide-scattered distribution of irrigated areas it would only be of local importance

On a global scale a change of 2500 kms is insignificant (= 05 Ofo) comshypared with a global E = P 496 X 103 kms or Es (oceans) = 415 X 103

kma The oceans will remain the great buffer of the water budget (Flohn 1913 a) smoothing man-made variations on land as long as their surface properties remain unaltered by chemical or biological pollution and as long as the solar constant remains really constant (which we still do not know) Table 1 B contains a regional short-lived phenomenon the suppresshysion of equatorial upwelling in the Pacific during an EI Nino episode in this case solar energy is no longer used to warm the upwelling cool water and hence is available for evaporation - which has far-reaching climatic effects

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

Hermann Flohn

Sensitivity of the arctic sea-ice and its consequences

Taking a future warming with increasing EL for granted (Fig 3 d also Lvovich 1969 Flohn 1973 a 1977 Broecker 1975 Schneider 1975 Kelshylogg 1976) would this not be a beneficial modification of our climate and all the better if it could be supported and even accelerated Unfortunately this is not the case owing among other factors to the high sensitivity of the arctic air and sea ice system (Flohn 1973 b Budyko 1974) This is demonstrated by its large variability during the last 5000 years and its strong correlation with the position of the large-scale circulation patterns

The arctic sea-ice with an average extension of approx 105 X IOU kID (March I2 to September 8) consists of individual ice-floes with an average lifetime (of an ice-crystal) of 5-6 years and an average thickness of 2-3 m though varying between 05 and more than 6 m This drifting ice decays from above during the melting-period (mid-June to end of August) while it grows from below during the rest of the year This occurs in a shallow ( 50 m) low-saline upper layer of the Arctic Ocean maintained from inflow from the large freshwater rivers of Siberia and Canada Thus the ice is very sensitive to any changes in the length and intensity of the melting

PROJECTIONS OF GLOBAL TEMPERATURE

AT JlMBudyko 1974 ~WKellogg 19764degC

i incl Trace Gases

Expected Range3deg incl C02 Effect

JM Mitchell (1977)

2deg

I without C02

1deg

0deg Natural Fluctuations

-1deg 1850 1900 2000

Figure 3 - Projections of global temperature (Budyko 1974 Kellogg 1976 Mitcbell 1977) assuming constancy of natural effects (see text)

2100

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

53 Some Aspects of Man-Made Climate Modification and Desertification

and growing seasons as well as to density variation in the stratified ocean Most probably its central core has been maintained since 1-2 million years ago

In the northern Atlantic the ice boundary receded before the Viking expeditions (800-1200 AD) as well as 5000 years ago up to northern Greenland and spread southwards 200 years ago towards the Faroe and Shetland islands Thickness variations are documented but doubtful they should be correlated with the observed surface temperature variations which are 3-4 times as large as those in the mid-latitudes

Historical evidence (Budyko 1974 National Academy of Sciences 1975) shows that hemispheric temperature variations of 1-15 degC coincide with advances and retreats of the arctic sea-ice of up to 2000 km in the Atlantic section this indcates its key role in climatic evolution If the CO2

content of the atmosphere varies by 50 or more together with the other above-mentioned warming effects drastic manges in that region must be envisaged which may perhaps even grow to a rapid and complete disshyappearance of the sea-ice

Among specialists there is little doubt about the possibility of an iceshyfree Arctic Ocean such an evolution would soon become irreversible The high solar radiation during the polar summer would be stored in the ocean and would lead to a rapid warming of surface waters and air especially during winter Since the temperature gradient from the Equator to the poles controls the position of the large-scale climatic belts of winds and precipitation (Flohn 1973 a) we have to expect together with an open Arctic Ocean a shift of these belts by some 3 00-600 km to the north in the Northern Hemisphere with severe consequences for the water-budget of densely populated areas Large increases of snowfall and snow-cover should also be expected along the relatively dry coasts of the Arctic Ocean including northern Greenland and the Canadian Arctic Archipelago

It should be added that any substantial diversion of fresh water from rivers running into the Arctic Ocean for irrigation or other purposes would accelerate this melting of the ice due to the increasing salinity and density of the shallow upper layer of sea water

Role of land-use conversion

It has been pointed out (Sawyer 1965) that large-scale weather phenoshymena are produced by differential heating only when this occurs on a synoptic scale i e over closed areas with a magnitude in the range of 105 or 108 km2 and when the heating function varies locally by about 20 Wm2 or more This excludes local point sources such as power stations

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

54 Hermann Flohn

or power parks their effect is restricted to the local scale e g to the frequency and or intensity of showers and thunderstorms

Inadvertently man has changed the surface conditions of the earth through many millennia to a very considerable extent - by conversion of forests into arable land by conversion of natural grasslands into pastures and by many processes of devegetation The need for firewood is in many hitherto underdeveloped countries one of the most powerful causes for this steady and often irreversible process which extends and intensifies with increasing pressure from a rising population

Estimating the areas which have been affected by this process since the beginning of agriculture a total of 45 X Idl km or about 30 Ofo of the surface of the continent is still conservative The process had been started even earlier when man learned to change his environment with the use of fire which may have happened for hunting purposes already in the palaeoshylithic age

The destruction of the natural vegetation leads nearly everywhere to an increase of the reflectivity (albedo) of the surface and thus decreases the amount of (absorbed) solar radiation Two examples may be given the typical albedo of a tropical rainforest is 012-014 while that of a humid grassland or cropland is 020-022 a typical albedo of a green (yellow) steppe is 020 (025) while that of a desert with bright sandy soil ranges around 035 These values are given for the visible part of the spectrum (035-07 pm) in the near infra-red (07-3 pm) part even higher values have been observed (Otterman 1974)

Mans activity e g protection of large farmland or grassland areas against herds of nomadic tribes can thus create significant horizontal difshyferences of the heat budget In some cases the bright surface of a desert may even be cooler than the darker surface of a desertic steppe but one has to take into account also the local change in the evaporation as inshydicated earlier in this paper In a partially humid climate any decrease of evapotranspiration of living plants is replaced by an increase in direct heating of the air (flux of sensible heat from surface to air)

The role of surface albedo has been best demonstrated in the radiative model of Manabe amp Wetherald (1967) increased surface albedo leads to

a (nearly linear) decrease of the surface equilibrium temperature (about - 12 degC with an albedo increase of 001) The large-scale role of the surface albedo has been strikingly evidenced by satellite data (Raschke et aI 1973) during July the Sahara and neighbouring deserts act as one of the main heat-sinks (i e cold sources) of the northern hemisphere shysimilarly to the deserts of the southern continents during the southern summer This unexpected but convincingly verified result motivated

55 Some Aspects of Man-Made Climate Modification and Desertification

Charney (1975) to a model experiment in which he showed that a drastic albedo increase results in a likewise drastic reduction of rainfall (which is prevented by increasing subsidence and heat-import necessary to replace the loss of energy to space) Because of the great significance of this result it has been checked and verified using several other models for the general (or local) circulation of the atmosphere (e g Berkofsky 1976)

This process aggravates the existing circulation above the great deserts of the globe in relation to the increasing man-made desertification process (Hare 1976 1977) It may have contributed to some extent to the very gradual desiccation of the margins of the desert since the last moist period which ended around 4000 years before the present i e after the beginning of the great civilizations of the past such as the Old Empire of Egypt and the Indus Culture However this quite slowly spreading process of desertishyfication has been overshadowed by the much larger natural climatic variashytions of the past now it increases and accelerates practically before our eyes intensified by the increase of population and its herds and also by some technological developments The recent Sahel drought (1968-73) was basically a consequence of large-scale circulation anomalies (of natural origin) similar to earlier droughts (1941-43 1908-13 and in the 19th and 18th centuries)

In a large-scale comparison the man-triggered degradation of the nashytural vegetation has locally quite different even opposing consequences (see above) These include

a) Reduction of absorbed solar energy due to higher albedo cooling b) Reduction of plant evapotranspiration drying c) Replacement of flux of latent heat by flux of sensible heat warming

It should be mentioned that under certain circumstances (except in mountains) a reversal of such degradation is possible if strict protection of the vegetation is maintained examples at average rainfalls of 70 mm (southern Tunisia) ISO mm (near Khartoum) and 250 mm (near Jodhshypur) demonstrate this capability for recovery Construction of large resershyvoirs and conversion of arid lands by irrigation leads to increased evaposhytranspiration and to (local) cooling

One of the largest conversion projects is now being carried out in the Amazon basin In addition to the ecological consequences it should be mentioned that from the climatological point of view the area is parshyticularly sensitive to such environmental changes the high rainfall is mainshytained by a large-scale convergence of water-vapour transport together with high evapotranspiration and the orographic barrier of the Andes The regional circulation leads during the southern summer to a permanent

Hermann Flohn

high-level anticyclone (Kreuels et al 1975) This whole system might be altered if the regional evapotranspiration over an area of nearly IO X loll

km2 is drastically reduced a significant decrease of rainfall and runoff of this (semi-closed) system cannot be excluded

Until the beginning of our century such changes of the land-use pattern went at a comparatively slow pace with increasing population especially in developing countries and modem technology the rate of change is in- fIIIIIII creasing rapidly As an example the tropical rain-forest of the Ivory Coast diminished from 1954-57 to 1966 from 75 010 to 536010 (in absolute figures by 28000 km in 10 years quoted from Synnott 1977)

Conclusion a scenario

Any attempt to speculate about climatic evolution during the next censhytury must be based on the assumption that the unpredictable natural causes of climatic variation remain without major impact We make the following assumptions (Flohn 1973 b)

a) Constancy of the solar constant b) No unusual frequency or clustering of heavy volcanic eruptions c) No unusual advance of the antarctic ice-shelf and d) No significant variation of the average global cloudiness

The present situation in the field of climate modelling and the multitude of (mostly non-linear) feedback mechanisms within the climatic system prevent an early solution to problems concerning the prediction of climatic variations even if we accept the above-mentioned assumptions without further discussion In addition to this the growth rates of energy consumpshytion and of the CO2 content of the atmosphere and likewise of other trace gases depend on many social and economic developments and on political decisions they are also largely unpredictable

Under such conditions we can only try to imagine what would happen if a further increase (not necessarily exponential) in man-made effects due to increased human population were extrapolated This would give us a scenario leading into the 21st century with its speed depending on the future political economic and social evolution - d Budyko 1974 Broecker 1975 Kellogg 1976 Flohn 1976 Mitchell 1977 WMO Techshynical Committee Panel of Experts 1977

We should expect around (or slightly before) the tum of the century a climatic situation similar to the period 1930-60 with its unusually high temperatures Later on we may expect a climate like that of the early Middle Ages (Viking period) or like that of the climatic optimum of

57 Some Aspects of Man-Made Climate Modification and Desertification

about 6000 BP at least this evolution is much more likely than a return to the Little Ice-age of between 1600 and 1850 with its extreme varishyability Intensive studies of the historical patterns of climate in that period are urgently needed whatever happened may indeed happen again (Bryson 19741975)middot

The last stage of this evolution - probably not before mid-century shymight be the irreversible transition to an ice-free Arctic Ocean with its unimaginable consequences on climate and economy and probably in a short time (such as a few decades) According to the indications of deepshysea cores such a pattern (with a very different climate in the Arctic) has never occurred in at least the last 150000 years and most probably not in the last 1-2 million years (National Academy of Sciences 1975)

Any reasonable estimate of the climatic pattern that would accompany an ice-free Arctic Ocean can only be obtained from model studies which have up to now yielded widely varying results An adaptation of a world population of 10-15 thousand millions to such an unprecedented true climatic catastrophe - especially regarding fresh water and food supply seems to be inconceivable Such an evolution could be avoided only if the energy problem could be controlled at an international level and if the mesmerizing idea of unlimited growth - which necessarily leads to overshyshooting and disaster - can be overcome by an acceptable compromise It is our generation which bears responsibility for a global-scale problem that will be facing our grandchildren let us take care to match the challenge and remember that there is all too little time left

Authors address Prof Dr Hermann Flohn Meteorologismes Institut der Universitat Bonn Auf dem Hiigelzo D-S 300 Bonn

REFERENCES

BACH W Review of Geophysics and Space Physics 14 (1976) PP42-74 BAUMGARTNER A and E REICHEL The World Water Balance Munich

1975 179 pp BERGTHORSSON P Jokull 19 1969 pp 94-101 BERKOFSKY L The effect of variable surface albedo on the atmospheric

circulation in desert regions In Joum Appl Meteor 15 1976 pp I 139 to 1144

BOLIN B Energy and Climate Stockholm 1975 p 55middot BROECKER W Science 1891975 pp 460-63 BRYSON R A A perspective on climatic change In Science 184 1974

PPmiddot753-60 BRYSON R A The lessons of climatic history In Environmental Consershy

vation2 (3) I975PP 163-708 figs

58 Hermann F10hn

BUDYKO M J Izmenenija Klimata Gidrometeoizdat Leningrad 1974 260 pp

CHARNEY J Dynamics of deserts and drought in the Sahel In Quart Joum Roy Meteor Soc 101 1975 pp 193-202

FLOHN H Naturwissenschaften 601973 a pp 340-48 FLOHN H Bonner Meteor AbhandI 19 1973 b FLOHN H Bild der Wissenschaft November 1975 Climatic Change I

1977i pp 82-88 HARE F K Climate and Desertification Component Review for the

United Nations Conference on Desertification (Preprint Toronto 189 pp) illustr 1976

HARE F K Connections between climate and desertification In Environshymental Conservation 4 (2) 1977 pp 81-9deg5 figs

KELLOGG W W Effects of Human Activities on Global Climate WMO Report October 1976

KREUELS R K FRAEDRICH and E RUPRECHT An aerological climatology of South America In Meteor Rundsch 28 1975 pp 17-24

LANDSBERG H Science 170 1970 pp I265-74 LVOVICH M J Water Resources for the Future [in Russian] Moscow

1969 MANABE S and R T WETHERALD Journ Atmos Sci 321975 pp 3-15 MANABE S and R T WETHERALD Thermal equilibrium of the atmosphere

with a given distribution of relative humidity In Joum Atmos Sci 24 1967 pp 241-59

MITCHELL J M jr Quaternary Research 6 1976 pp 481-93 MITCHELL J M jr Environmental Data Service Magazine March 1977 NATIONAL ACADEMY OF SCIENCES Understanding Climatic Change Natioshy

nal Academy of Sciences Washington DC 1974 pp 53 1-33 OITERMANN J Baring high-albedo soils by overgrazing A hypothesized

desertification mechanism In Science 186 1974 pp 531-33 RASCHKE E et aI The annual radiation balance of the earth-atmosphere

system during 1969-70 from Nimbus-3 measurements In Joum Atmos Sci 301973 pp 341-64

SAWYER J S Notes on the possible physical causes of long-term weather anomalies WMO Technical Note 661965 pp 227-48

SCHNEIDER S The Genesis Strategy New York 1975 419 pp SMIC Report Inadvertent Climate Modification Report of the Study of

Mans Impact on Climate (SMIC) MIT Press Cambridge Massachushysetts 1971 308 pp

SYNNOIT T J Monitoring Tropical Forests A Review with Special Reference to Africa Monitoring and Assessment Center of SCOPE Report No 51977

WANG W C et al Science 194 1976 pp 685-9deg WMO Executive Committee Panel of Experts Technical Report WMO

Bulletin 26 1977 pp 50-55 WMO-JCSU Joint Organizing Committee The Physical Basis of Climate

and Climate Modelling GARP Publication Series No 16 Geneva 1975 265 pp

_A

J

Hermann Flohn

high-level anticyclone (Kreuels et al 1975) This whole system might be altered if the regional evapotranspiration over an area of nearly IO X loll

km2 is drastically reduced a significant decrease of rainfall and runoff of this (semi-closed) system cannot be excluded

Until the beginning of our century such changes of the land-use pattern went at a comparatively slow pace with increasing population especially in developing countries and modem technology the rate of change is in- fIIIIIII creasing rapidly As an example the tropical rain-forest of the Ivory Coast diminished from 1954-57 to 1966 from 75 010 to 536010 (in absolute figures by 28000 km in 10 years quoted from Synnott 1977)

Conclusion a scenario

Any attempt to speculate about climatic evolution during the next censhytury must be based on the assumption that the unpredictable natural causes of climatic variation remain without major impact We make the following assumptions (Flohn 1973 b)

a) Constancy of the solar constant b) No unusual frequency or clustering of heavy volcanic eruptions c) No unusual advance of the antarctic ice-shelf and d) No significant variation of the average global cloudiness

The present situation in the field of climate modelling and the multitude of (mostly non-linear) feedback mechanisms within the climatic system prevent an early solution to problems concerning the prediction of climatic variations even if we accept the above-mentioned assumptions without further discussion In addition to this the growth rates of energy consumpshytion and of the CO2 content of the atmosphere and likewise of other trace gases depend on many social and economic developments and on political decisions they are also largely unpredictable

Under such conditions we can only try to imagine what would happen if a further increase (not necessarily exponential) in man-made effects due to increased human population were extrapolated This would give us a scenario leading into the 21st century with its speed depending on the future political economic and social evolution - d Budyko 1974 Broecker 1975 Kellogg 1976 Flohn 1976 Mitchell 1977 WMO Techshynical Committee Panel of Experts 1977

We should expect around (or slightly before) the tum of the century a climatic situation similar to the period 1930-60 with its unusually high temperatures Later on we may expect a climate like that of the early Middle Ages (Viking period) or like that of the climatic optimum of

57 Some Aspects of Man-Made Climate Modification and Desertification

about 6000 BP at least this evolution is much more likely than a return to the Little Ice-age of between 1600 and 1850 with its extreme varishyability Intensive studies of the historical patterns of climate in that period are urgently needed whatever happened may indeed happen again (Bryson 19741975)middot

The last stage of this evolution - probably not before mid-century shymight be the irreversible transition to an ice-free Arctic Ocean with its unimaginable consequences on climate and economy and probably in a short time (such as a few decades) According to the indications of deepshysea cores such a pattern (with a very different climate in the Arctic) has never occurred in at least the last 150000 years and most probably not in the last 1-2 million years (National Academy of Sciences 1975)

Any reasonable estimate of the climatic pattern that would accompany an ice-free Arctic Ocean can only be obtained from model studies which have up to now yielded widely varying results An adaptation of a world population of 10-15 thousand millions to such an unprecedented true climatic catastrophe - especially regarding fresh water and food supply seems to be inconceivable Such an evolution could be avoided only if the energy problem could be controlled at an international level and if the mesmerizing idea of unlimited growth - which necessarily leads to overshyshooting and disaster - can be overcome by an acceptable compromise It is our generation which bears responsibility for a global-scale problem that will be facing our grandchildren let us take care to match the challenge and remember that there is all too little time left

Authors address Prof Dr Hermann Flohn Meteorologismes Institut der Universitat Bonn Auf dem Hiigelzo D-S 300 Bonn

REFERENCES

BACH W Review of Geophysics and Space Physics 14 (1976) PP42-74 BAUMGARTNER A and E REICHEL The World Water Balance Munich

1975 179 pp BERGTHORSSON P Jokull 19 1969 pp 94-101 BERKOFSKY L The effect of variable surface albedo on the atmospheric

circulation in desert regions In Joum Appl Meteor 15 1976 pp I 139 to 1144

BOLIN B Energy and Climate Stockholm 1975 p 55middot BROECKER W Science 1891975 pp 460-63 BRYSON R A A perspective on climatic change In Science 184 1974

PPmiddot753-60 BRYSON R A The lessons of climatic history In Environmental Consershy

vation2 (3) I975PP 163-708 figs

58 Hermann F10hn

BUDYKO M J Izmenenija Klimata Gidrometeoizdat Leningrad 1974 260 pp

CHARNEY J Dynamics of deserts and drought in the Sahel In Quart Joum Roy Meteor Soc 101 1975 pp 193-202

FLOHN H Naturwissenschaften 601973 a pp 340-48 FLOHN H Bonner Meteor AbhandI 19 1973 b FLOHN H Bild der Wissenschaft November 1975 Climatic Change I

1977i pp 82-88 HARE F K Climate and Desertification Component Review for the

United Nations Conference on Desertification (Preprint Toronto 189 pp) illustr 1976

HARE F K Connections between climate and desertification In Environshymental Conservation 4 (2) 1977 pp 81-9deg5 figs

KELLOGG W W Effects of Human Activities on Global Climate WMO Report October 1976

KREUELS R K FRAEDRICH and E RUPRECHT An aerological climatology of South America In Meteor Rundsch 28 1975 pp 17-24

LANDSBERG H Science 170 1970 pp I265-74 LVOVICH M J Water Resources for the Future [in Russian] Moscow

1969 MANABE S and R T WETHERALD Journ Atmos Sci 321975 pp 3-15 MANABE S and R T WETHERALD Thermal equilibrium of the atmosphere

with a given distribution of relative humidity In Joum Atmos Sci 24 1967 pp 241-59

MITCHELL J M jr Quaternary Research 6 1976 pp 481-93 MITCHELL J M jr Environmental Data Service Magazine March 1977 NATIONAL ACADEMY OF SCIENCES Understanding Climatic Change Natioshy

nal Academy of Sciences Washington DC 1974 pp 53 1-33 OITERMANN J Baring high-albedo soils by overgrazing A hypothesized

desertification mechanism In Science 186 1974 pp 531-33 RASCHKE E et aI The annual radiation balance of the earth-atmosphere

system during 1969-70 from Nimbus-3 measurements In Joum Atmos Sci 301973 pp 341-64

SAWYER J S Notes on the possible physical causes of long-term weather anomalies WMO Technical Note 661965 pp 227-48

SCHNEIDER S The Genesis Strategy New York 1975 419 pp SMIC Report Inadvertent Climate Modification Report of the Study of

Mans Impact on Climate (SMIC) MIT Press Cambridge Massachushysetts 1971 308 pp

SYNNOIT T J Monitoring Tropical Forests A Review with Special Reference to Africa Monitoring and Assessment Center of SCOPE Report No 51977

WANG W C et al Science 194 1976 pp 685-9deg WMO Executive Committee Panel of Experts Technical Report WMO

Bulletin 26 1977 pp 50-55 WMO-JCSU Joint Organizing Committee The Physical Basis of Climate

and Climate Modelling GARP Publication Series No 16 Geneva 1975 265 pp

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J

57 Some Aspects of Man-Made Climate Modification and Desertification

about 6000 BP at least this evolution is much more likely than a return to the Little Ice-age of between 1600 and 1850 with its extreme varishyability Intensive studies of the historical patterns of climate in that period are urgently needed whatever happened may indeed happen again (Bryson 19741975)middot

The last stage of this evolution - probably not before mid-century shymight be the irreversible transition to an ice-free Arctic Ocean with its unimaginable consequences on climate and economy and probably in a short time (such as a few decades) According to the indications of deepshysea cores such a pattern (with a very different climate in the Arctic) has never occurred in at least the last 150000 years and most probably not in the last 1-2 million years (National Academy of Sciences 1975)

Any reasonable estimate of the climatic pattern that would accompany an ice-free Arctic Ocean can only be obtained from model studies which have up to now yielded widely varying results An adaptation of a world population of 10-15 thousand millions to such an unprecedented true climatic catastrophe - especially regarding fresh water and food supply seems to be inconceivable Such an evolution could be avoided only if the energy problem could be controlled at an international level and if the mesmerizing idea of unlimited growth - which necessarily leads to overshyshooting and disaster - can be overcome by an acceptable compromise It is our generation which bears responsibility for a global-scale problem that will be facing our grandchildren let us take care to match the challenge and remember that there is all too little time left

Authors address Prof Dr Hermann Flohn Meteorologismes Institut der Universitat Bonn Auf dem Hiigelzo D-S 300 Bonn

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BACH W Review of Geophysics and Space Physics 14 (1976) PP42-74 BAUMGARTNER A and E REICHEL The World Water Balance Munich

1975 179 pp BERGTHORSSON P Jokull 19 1969 pp 94-101 BERKOFSKY L The effect of variable surface albedo on the atmospheric

circulation in desert regions In Joum Appl Meteor 15 1976 pp I 139 to 1144

BOLIN B Energy and Climate Stockholm 1975 p 55middot BROECKER W Science 1891975 pp 460-63 BRYSON R A A perspective on climatic change In Science 184 1974

PPmiddot753-60 BRYSON R A The lessons of climatic history In Environmental Consershy

vation2 (3) I975PP 163-708 figs

58 Hermann F10hn

BUDYKO M J Izmenenija Klimata Gidrometeoizdat Leningrad 1974 260 pp

CHARNEY J Dynamics of deserts and drought in the Sahel In Quart Joum Roy Meteor Soc 101 1975 pp 193-202

FLOHN H Naturwissenschaften 601973 a pp 340-48 FLOHN H Bonner Meteor AbhandI 19 1973 b FLOHN H Bild der Wissenschaft November 1975 Climatic Change I

1977i pp 82-88 HARE F K Climate and Desertification Component Review for the

United Nations Conference on Desertification (Preprint Toronto 189 pp) illustr 1976

HARE F K Connections between climate and desertification In Environshymental Conservation 4 (2) 1977 pp 81-9deg5 figs

KELLOGG W W Effects of Human Activities on Global Climate WMO Report October 1976

KREUELS R K FRAEDRICH and E RUPRECHT An aerological climatology of South America In Meteor Rundsch 28 1975 pp 17-24

LANDSBERG H Science 170 1970 pp I265-74 LVOVICH M J Water Resources for the Future [in Russian] Moscow

1969 MANABE S and R T WETHERALD Journ Atmos Sci 321975 pp 3-15 MANABE S and R T WETHERALD Thermal equilibrium of the atmosphere

with a given distribution of relative humidity In Joum Atmos Sci 24 1967 pp 241-59

MITCHELL J M jr Quaternary Research 6 1976 pp 481-93 MITCHELL J M jr Environmental Data Service Magazine March 1977 NATIONAL ACADEMY OF SCIENCES Understanding Climatic Change Natioshy

nal Academy of Sciences Washington DC 1974 pp 53 1-33 OITERMANN J Baring high-albedo soils by overgrazing A hypothesized

desertification mechanism In Science 186 1974 pp 531-33 RASCHKE E et aI The annual radiation balance of the earth-atmosphere

system during 1969-70 from Nimbus-3 measurements In Joum Atmos Sci 301973 pp 341-64

SAWYER J S Notes on the possible physical causes of long-term weather anomalies WMO Technical Note 661965 pp 227-48

SCHNEIDER S The Genesis Strategy New York 1975 419 pp SMIC Report Inadvertent Climate Modification Report of the Study of

Mans Impact on Climate (SMIC) MIT Press Cambridge Massachushysetts 1971 308 pp

SYNNOIT T J Monitoring Tropical Forests A Review with Special Reference to Africa Monitoring and Assessment Center of SCOPE Report No 51977

WANG W C et al Science 194 1976 pp 685-9deg WMO Executive Committee Panel of Experts Technical Report WMO

Bulletin 26 1977 pp 50-55 WMO-JCSU Joint Organizing Committee The Physical Basis of Climate

and Climate Modelling GARP Publication Series No 16 Geneva 1975 265 pp

_A

J

58 Hermann F10hn

BUDYKO M J Izmenenija Klimata Gidrometeoizdat Leningrad 1974 260 pp

CHARNEY J Dynamics of deserts and drought in the Sahel In Quart Joum Roy Meteor Soc 101 1975 pp 193-202

FLOHN H Naturwissenschaften 601973 a pp 340-48 FLOHN H Bonner Meteor AbhandI 19 1973 b FLOHN H Bild der Wissenschaft November 1975 Climatic Change I

1977i pp 82-88 HARE F K Climate and Desertification Component Review for the

United Nations Conference on Desertification (Preprint Toronto 189 pp) illustr 1976

HARE F K Connections between climate and desertification In Environshymental Conservation 4 (2) 1977 pp 81-9deg5 figs

KELLOGG W W Effects of Human Activities on Global Climate WMO Report October 1976

KREUELS R K FRAEDRICH and E RUPRECHT An aerological climatology of South America In Meteor Rundsch 28 1975 pp 17-24

LANDSBERG H Science 170 1970 pp I265-74 LVOVICH M J Water Resources for the Future [in Russian] Moscow

1969 MANABE S and R T WETHERALD Journ Atmos Sci 321975 pp 3-15 MANABE S and R T WETHERALD Thermal equilibrium of the atmosphere

with a given distribution of relative humidity In Joum Atmos Sci 24 1967 pp 241-59

MITCHELL J M jr Quaternary Research 6 1976 pp 481-93 MITCHELL J M jr Environmental Data Service Magazine March 1977 NATIONAL ACADEMY OF SCIENCES Understanding Climatic Change Natioshy

nal Academy of Sciences Washington DC 1974 pp 53 1-33 OITERMANN J Baring high-albedo soils by overgrazing A hypothesized

desertification mechanism In Science 186 1974 pp 531-33 RASCHKE E et aI The annual radiation balance of the earth-atmosphere

system during 1969-70 from Nimbus-3 measurements In Joum Atmos Sci 301973 pp 341-64

SAWYER J S Notes on the possible physical causes of long-term weather anomalies WMO Technical Note 661965 pp 227-48

SCHNEIDER S The Genesis Strategy New York 1975 419 pp SMIC Report Inadvertent Climate Modification Report of the Study of

Mans Impact on Climate (SMIC) MIT Press Cambridge Massachushysetts 1971 308 pp

SYNNOIT T J Monitoring Tropical Forests A Review with Special Reference to Africa Monitoring and Assessment Center of SCOPE Report No 51977

WANG W C et al Science 194 1976 pp 685-9deg WMO Executive Committee Panel of Experts Technical Report WMO

Bulletin 26 1977 pp 50-55 WMO-JCSU Joint Organizing Committee The Physical Basis of Climate

and Climate Modelling GARP Publication Series No 16 Geneva 1975 265 pp

_A

J