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Arctic Melt

Charlie Zender <[email protected]>Department of Earth System Science

University of California, Irvine

Presented to: Osher Lifelong Learning Institute (OLLI)October 31, 2006

(Web: http://dust.ess.uci.edu/smn/smn arc mlt olli 200610.pdf)

http://www.ess.uci.edu/~zender

mailto:[email protected]

http://www.ess.uci.edu

http://unex.uci.edu/community/olli/index.asp?

http://dust.ess.uci.edu/smn/smn_arc_mlt_olli_200610.pdf

Abstract

The Arctic is melting . . . fast.

IMPACTS OF A WARMING ARCTIC

1

Most of the heat energy emittedfrom the surface is absorbed bygreenhouse gases which radiateheat back down to warm thelower atmosphere and the surface.Increasing the concentrations ofgreenhouse gases increases thewarming of the surface and slowsthe loss of heat energy to space.

The Earth’s Greenhouse Effect

The

surfa

cecools by radiating heat energy

upward.

©2004, ACIA


2

1000 Years of Changes in Carbon Emissions, CO2 Concentrations and Temperature

This 1000-year record tracks the rise incarbon emissions due to human activities(fossil fuel burning and land clearing) andthe subsequent increase in atmosphericcarbon dioxide concentrations, and airtemperatures. The earlier parts of thisNorthern Hemisphere temperature recon-struction are derived from historical data,tree rings, and corals, while the later partswere directly measured. Measurements ofcarbon dioxide (CO2) in air bubbles trappedin ice cores form the earlier part of theCO2 record; direct atmospheric measure-ments of CO2 concentration began in 1957.

©2004, ACIA


3

This record illustrates the relationship betweentemperature and atmospheric carbon dioxide concentrations over the past 160 000 years and thenext 100 years. Historical data are derived from icecores, recent data were directly measured, andmodel projections are used for the next 100 years.

©2004, ACIA

Atmospheric Carbon DioxideConcentration and

Temperature Change

Why Does the Arctic Warm Faster than Lower Latitudes?1. As snow and ice melt,darker land and ocean surfaces absorb more

solar energy.2. More of the extra trapped

energy goes directly intowarming rather than

into evaporation.

3. The atmospheric layer thathas to warm in order

to warm the surface is shallower in the Arctic.

4. As sea ice retreats,solar heat absorbed by the

oceans is more easily transferred to the atmosphere.

5. Alterations in atmosphericand oceanic circulation can

increase warming.


6

©2004, ACIA/ Map ©Clifford Grabhorn


7

100000 Years of Temperature Variation in Greenland

This record of temperature change (departures from present conditions) has been reconstructed from a Greenland ice core. The record demonstrates the high variability of the climate over the past 100 000 years. It also suggests that the climate of the past 10000years or so, which was the time during which human civilization developed, has been unusu-ally stable. There is concern that the rapid warming caused by the increasing concentrationsof greenhouse gases due to human activities could destabilize this state.

Thousands of Years Before Present©2004, ACIA


8

©2004, ACIA

Annual average change in near surface air temperature fromstations on land relative to the average for 1961-1990, forthe region from 60 to 90˚N.

Observed Arctic Temperature, 1900 to Present


9

Observed Surface Air Temperature Changes: 1954-2003 (WINTER: Dec-Feb in ˚C)

This map indicates the temperature change during the wintermonths, ranging from a warming of up to 4˚C in Siberia andNorthwest Canada to a cooling of 1˚C over southern Greenland.

No Data Available

©2004, ACIA/ map ©Clifford Grabhorn

Observed Surface Air Temperature Changes: 1954-2003 (ANNUAL, ˚C)

+4

+3

+2

+1

0˚C

-1

-2

No Data Available


The colors indicate the change in temperature from 1954 to 2003.The map indicates annual average temperature change, whichranges from a 2-3˚C warming in Alaska and Siberia to a coolingof up to 1˚C in southern Greenland.


10

Observed seasonal Arctic sea-ice extent (1900-2003)

Annual average extent of arctic sea ice from 1900 to 2003. Adecline in sea-ice extent began about 50 years ago and thisdecline sharpened in recent decades, corresponding with thearctic warming trend. The decrease in sea-ice extent duringsummer is the most dramatic of the trends.

©2004, ACIA


11

Observed sea ice September 1979 Observed sea ice September 2003

The two images above, constructed from satellite data, compare arctic sea ice concentrations in September of 1979 and 2003. September is themonth in which sea ice is at its yearly minimum and 1979 marks the first year that data of this kind became available in meaningful form. Thelowest concentration of sea ice on record was in September 2002.

©NASA


12

Projections of global temperature change (shown as depar-tures from the 1990 temperature) from 1990 to 2100 forseven illustrative emissions scenarios. The brown line showsthe projection of the B2 emissions scenario, the primary sce-nario used in this assessment, and the scenario on which themaps in this report showing projected climate changes arebased. The pink line shows the A2 emissions scenario, used toa lesser degree in this assessment. The dark gray band showsthe range of results for all the SRES emissions scenarios withone average model while the light gray band shows the fullrange of scenarios using various climate models.

Projected Global Temperature Rise

©2004, ACIA

Projected Arctic Surface Air Temperatures 2000-210060˚N - Pole: Change from 1981-2000 average

The ten lines show air temperatures for the region from 60˚Nto the pole as projected by each of the five ACIA global cli-mate models using two different emissions scenarios. The pro-jections remain similar through about 2040, showing about a2˚C temperature rise, but then diverge, showing increases fromaround 4˚ to over 7˚C by 2100. The full range of models andscenarios reviewed by the IPCC cover a wider range of possiblefutures. Those used in this assessment fall roughly in the mid-dle of this range, and thus represent neither best- nor worst-case scenarios.

©2004, ACIA


14

Projected Surface Air Temperature Change1990s-2090s in ˚C (Winter: Dec-Feb)


These maps show the projected temperature change from the 1990s to the 2090s, based on the average change calculated by the five ACIA climatemodels using the lower of the two emissions scenarios (B2) considered in this assessment. On these maps, orange indicates that an area is projectedto warm by about 6˚C from the 1990s to the 2090s.

Projected Surface Air Temperature Change1990s-2090s in ˚C (Annual)

+12

+10

+8

+6

+4

+2

0˚C



16

This graph shows percentage changes in aver-age precipitation projected by the five ACIAclimate models for the B2 emissions scenario.The heavy lines at the bottom are projectedaverage global precipitation changes and thethinner lines above are projected arctic precip-itation changes. As the results show, the pre-cipitation increases are projected to be muchgreater in the Arctic than for the world as awhole. It is also apparent that the year-to-year variability is much greater in the Arctic.

Projected Precipitation Change (% change from 1981-2000 average)

Arct

icG

loba

l

©2004, ACIA


18

+12

+10

+8

+6

+4

+2

0˚C

Projected WinterSurface Air Temperature

Change:1990s - 2090s ˚C

Observed Ice ExtentSeptember 2002

Projected Ice Extent2070 - 2090

2040 - 2060

2010 - 2030

Projected Changes in Sea Ice


Sea ice has already declinedconsiderably over the pasthalf century. Additionaldeclines of roughly 10-50% inannual average sea-ice extentare projected by 2100. Loss ofsea ice during summer is pro-jected to be considerablygreater than the annual aver-age decrease, with a 5-modelaverage projecting more thana 50% decline by the end ofthis century, and some modelsshowing near-complete disap-pearance of summer sea ice.The projected reductions insea ice will increase regionaland global warming by reduc-ing the reflectivity of theocean surface.


19

2010 - 2030 2040 - 2060

Projected Ice Extent (5-model average for September)

September sea-ice extent, already declining markedly, is projected to decline even more rapidly in the future. The three images above show the average of theprojections from five climate models for three future time periods. As the century progresses, sea ice moves further and further from the coasts of arctic landmasses, retreating to the central Arctic Ocean. Some models project the nearly complete loss of summer sea ice in this century.

2070 - 2090


May snow cover is projectedto decrease substantiallythroughout the Arctic.The gray area in the fig-ure shows the currentextent of May snowcover. The white area isthe projected area ofMay snow cover in the2070 to 2090 time peri-od based on ACIA modelprojections. The large-scale pattern of projectedsnow cover retreat inspring is apparent.


20

Snow Cover Observed and Projected (May)

Observed

Projected



23

Sea ice covered with snowreflects about 85-90% of sun-light, while ocean water reflectsjust 10%. Thus, as sea ice melts,revealing more and more of theocean beneath, the increasingabsorption of solar radiationadds to global warming, whichcauses more melting, which inturn causes more warming, andso on…

©2004, ACIA

Surface Reflectivity


24

Snow cover extent over arctic land areas hasdecreased by about 10% over the past 30years, with the most visible change being anearlier disappearance of snow in spring. Onelocal example is shown in the graph above,for Barrow, Alaska. Over the past 50 years, thesnow cover end date has shifted to about onemonth earlier.

Observed Snow Cover Change Barrow, Alaska

©2004, ACIA


25

Current Arctic Vegetation Projected Vegetation, 2090-2100

These maps of current and projected vegetation in the Arctic illustrate that forests are project-ed to overtake tundra and tundra is projected to move into polar deserts. These changes willresult in a darker land surface, amplifying warming by absorbing more of the sun’s energy andcreating a self-reinforcing feedback loop.

IcePolar Desert / Semi-desertTundraBoreal ForestTemperate ForestGrassland



32

Greenland Ice Sheet Melt Extent

1992 2002


Greenland Ice Sheet Melt Extent (Maximum melt extent 1979 - 2002)

(105 km2)

1980 1985 1990 1995 2000

7

6

5

4

3

2

©2004, ACIA

Seasonal surface melt extent on the Greenland Ice Sheet has been observed by satellite since 1979 and shows an increasing trend. The melt zone, where sum-mer warmth turns snow and ice around the edges of the ice sheet into slush and ponds of meltwater, has been expanding inland and to record high eleva-tions in recent years. When the meltwater seeps down through cracks in the ice sheet, it may accelerate melting and, in some areas, allow the ice to slidemore easily over the bedrock below, speeding its movement to the sea. In addition to contributing to global sea-level rise, this process adds freshwater to theocean, with potential impacts on ocean circulation and thus regional climate.


33

For the Arctic as a whole, there was a sub-stantial loss in glacial volume from 1961 to1998. Glaciers in the North American Arcticlost the most mass (about 450 km3), withincreased loss since the late 1980s. Glaciersin the Russian Arctic have also had largelosses (about 100 km3). Glaciers in theEuropean Arctic show an increase in volumebecause increased precipitation inScandinavia and Iceland added more to gla-cial mass than melting removed over thatperiod.

Cumulative Change in Volume of Arctic Glaciers since 1960

©2004, ACIA


35

A 50-cm rise in sea level will typically cause a shoreward retreatof coastline of 50 meters if the land is relatively flat (like mostcoastal plains), causing substantial economic, social, and environ-mental impacts.

Areas in Florida Subject to Inundation with 100Centimeter Sea Level Rise

©2004, ACIA


Coastline Retreat with Sea-level Rise

Sea-level rise is projected to have serious implications for coastalcommunities and industries, islands, river deltas, harbors, and thelarge fraction of humanity living in coastal areas worldwide.Sea-level rise will increase the salinity of bays and estuaries. Itwill increase coastal erosion, especially where coastal lands aresoft rather than rocky.


36

Projected Contribution of Arctic Land Iceto Sea-level Change

This chart compares the projected con-tributions to sea-level change due tomelting of land-based ice in variousparts of the Arctic. The Greenland IceSheet is projected to make the largestcontribution because of its size.Although Alaska’s glaciers cover a muchsmaller area, they are also projected tomake a large contribution. The totalcontribution of melting land-based icein the Arctic to global sea-level rise isprojected to be about 10 cm by 2100.The primary driver of sea-level rise isthermal expansion due to ocean warm-ing, and that is not included in thischart.

©2004, ACIA


1

Most of the heat energy emittedfrom the surface is absorbed bygreenhouse gases which radiateheat back down to warm thelower atmosphere and the surface.Increasing the concentrations ofgreenhouse gases increases thewarming of the surface and slowsthe loss of heat energy to space.

The Earth’s Greenhouse Effect

The

surfa

cecools by radiating heat energy

upward.

©2004, ACIA

0 1 2 3 4 5 6 7 8 9 10−0.16

−0.14

−0.12

−0.1

−0.08

−0.06

−0.04

−0.02

0

Time (days)

Alb

edo

Cha

nge

0 1 2 3 4 5 6 7 8 9 10−0.16

−0.14

−0.12

−0.1

−0.08

−0.06

−0.04

−0.02

0

Time (days)

Alb

edo

Cha

nge

SNICAR, dT/dz=20 K m−1



NCAR CLMVerseghy, 1991

Niwot, Jan2−Jan12, 11:00Niwot, Jan2−Jan12, 12:00Niwot, Jan2−Jan12, 13:00Niwot, Jan2−Jan12, 14:00

Figure 1: Observed and modeled albedo decay at Niwot Ridge January 2, 2001. (Flanner and Zender, 2006,JGR)

Figure 2: February 15 dust-fall in snowpack near Niwot Ridge, Colorado on May 17, 2006. (Courtesy TomPainter, NSIDC)

Figure 3: Present day global surface forcing by soot and dust in snowpack. Global mean ∼ 0.047 W m−2.

Month

Latit

ude

(°N

)Present BC+Dust Snow Forcing (W m−2)

J F M A M J J A S O N D0

10

20

30

40

50

60

70

80

0.15

0.30

0.45

0.60

0.75

0.90

1.05

1.20

1.35

1.50

Month

Latit

ude

(°N

)

Pres. BC+Dust/Snow ALBS Change


10

20

30

40

50

60

70

80

−0.20

−0.16

−0.11

−0.07

−0.02

0.02

0.07

0.11

0.16

0.20

Month

Latit

ude

(°N

)

Pres. BC+Dust/Snow QMELT Change (mm day−1)


10

20

30

40

50

60

70

80

−1.00

−0.78

−0.56

−0.33

−0.11

0.11

0.33

0.56

0.78

1.00

Month

Latit

ude

(°N

)

Pres. BC+Dust/Snow Temp. Change (° C)


10

20

30

40

50

60

70

80

−4.0

−3.1

−2.2

−1.3

−0.4

0.4

1.3

2.2

3.1

4.0

Figure 4: Present day climate response to soot and dust in snowpack.

1. Acknowledgements

Thanks to . . .

1. Arctic Climate Impact Assessment (ACIA, 2005)2. ESS Graduate student Mark Flanner3. Tom Painter, NSIDC

Funding provided by

1. National Science Foundation

http://www.acia.uaf.edu

2. References

References

ACIA, 2005: Arctic Climate Impact Assessment. Cambridge Univ. Press,New York.

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