Human Influences on Climate

• Greenhouse effect

• Feedbacks

• Northward movement of the jet streams

• Changing Land Surfaces

• Heat Islands

• Consequences of Greenhouse Effect

Simple Greenhouse Model

. befraction Let this

space.. intoback reflected isradiation thisofPart

Earth) theof radius theis (

Earth theof area sectional cross the times

issun by the blockedenergy totalThe

constant).

solar theas(known as areaunit per surface

sEarth' at thesun thefromenergy thedefine We

20

0

0

ee

A

RRQ

QE

Q

Greenhouse Effect

sphere) (aEarth theof area theis 4 where

4

relationBoltzmann -Stefan

by thegiven is radiatedenergy The space. into

backradiation red-infra radiates Earth then The .

re temperatua Earth to theupheat lenergy wil This

)1(

isEarth by the absorbedenergy totalThen the

2

24

20

e

eeR

e

eA

R

RTE

T

RQE

Greenhouse Effect

Why?K. 288 is etemperatur

mean actusl the whereas,255 then )7.0(

equation in the constants measured insert the When we4

)1(

or

4)1(

:out energy

theequalmust in energy theHence m.equilibriu

in thermal isEarth year the aover averagedWhen

04

2420

KT

QT

RTRQ

e

e

eee

Greenhouse Effect

feedback. -

change toresistant is system climate But the

larger. gets re temperatularger the gets As

)2/1(

)1(

:becomesequation

mequilibriu then the, radiation, infrared thermal

outgoing theoffraction a absorbs atmosphere theIf

04

QTe

Ice-albedo feedback effect

Positive Feedback

Negative Feedback

CLIMATE FEEDBACK MECHANISMS

• ·POSITIVE AND NEGATIVE FEEDBACKS

• ·WATER VAPOR - POSITIVE

• ·ICE COVER - POSITIVE

• .CLOUDS - POSITIVE AND NEGATIVE - MAINLY NEGATIVE

Fig. 7-27, p. 191

Positions of the jet streams

Jet Streams on March 11, 1990Sub-tropical = Blue, Polar = Red

Fig. 8-30, p. 231

Relation between jet stream and high and low pressure systems

% DAYS WHEN JETSREAM WITHIN 150 MILES OF BALTIMORE

Frontal Movement and Climate Change

• Increasing evidence that the Polar and Sub-tropical jet streams in the Northern Hemisphere are moving northward.

• This implies that the weather patterns associated with the jets (fronts) are also moving northward

• As the sub-tropical jet moves northward so do the high pressure systems associated with this jet.

• Expect drier summers• Could increase in greenhouse forcing in the

tropics lead to a stronger Hadley cell circulation, and hence to a movement of the jet?

Fig. 15.8

Disappearance of the Aral Sea, during the period from 1973 to 2000.

Largely due to diversion of water from the rivers feeding the sea for irrigation.

Aral Sea

• Government of the Soviet Union diverted waters feeding this inland lake to provide water for the growing of cotton.

• Aral Sea began shrinking rapidly

• Climate has also changed in the region

• Asian ‘Dust Bowl’

• Increased salinity destroyed fishing industry

Fig. 15.9

Roadways and buildings reduce evapor-transpiration and absorb more solar radiation than the surrounding rural regions.

Washington DC Heat Island

THE CLIMATE OF CITIES

• URBAN HEAT ISLAND• TEMPERATURES ARE GENERALLY HIGHER THAN

IN RURAL AREAS, CREATING AN 'ISLAND' OF WARMER AIR.

• CITIES ARE GENERALLY CLOUDIER, FOGGIER, WARMER, WETTER

• WHY?• ROCK-LIKE MATERIALS OF CITY HAVE HIGH

THERMAL CAPACITY• IMPERVIOUS SURFACES REMOVE PRECIPITATION

QUICKLY• LARGE SOURCES OF HEAT• ATMOSPHERIC POLLUTION TRAPS RADIATION• TALL BUILDINGS ALTER THE AIR FLOW• INCREASED PRECIPITATION• THERMALLY INDUCED UPWARD MOTIONS

Fig. 15-1, p. 442

CONSEQUENCES OF GREENHOUSE WARMING

• .WATER RESOURCES AND AGRICULTURE - CHANGES IN PRECIPITATION PATTERNS - LENGTH OF GROWING SEASON

• .SEA LEVEL RISE - .MELTING OF GLACIERS PLUS THE THERMAL EXPANSION OF THE OCEANS - HAS RISEN 10-25 CM OVER PAST CENTURY

• .NEW WEATHER PATTERNS - HIGHER FREQUENCY AND GREATER INTENSITY OF HURRICANES BECAUSE OF WARMER SEA SURFACE TEMPERATURES.

• SHIFTS IN PATHS OF CYCLONIC STORMS - PRECIPITATION PATTERNS.

• .SHIFTS OF OCCURRENCES OF TORNADOES. • .MORE INTENSE HEAT WAVES AND DROUGHTS IN

SOME REGIONS AND LESS IN OTHERS.