Arctic Sea Ice and the Ice-Albedo Feedback

Harry Stern, Polar Science Center, University of Washington, Seattle

Climate Complexity Workshop 2012May 9, 2012

Arctic Geography

Greenland

Alaska

Canada

Russia

Surface Area of the Earth

LANDPACIFIC OCEAN

ATLANTIC OCEAN

INDIAN OCEAN

ARCTIC OCEAN

0

10

20

30

40

29%

36%

18%14%

3%

SEA ICE forms from freezing saltwater.

The surface can be smooth or bumpy.

Sea ice can grow to be 10 feet thick or more.

ICEBERGS are chunks of glaciers that break off and float away.

They are made of freshwater ice (no salt) from many years of compressed snowfall.

January

Monthly averagesea ice concentration from satellite data

National Snow and Ice Data Center (NSIDC), Boulder, CO

February

March

April

May

June

July

August

September

October

November

December

Courtesy of NSIDC, Boulder, CO

September Arctic Sea Ice Trends, 1979-2011

What is a Feedback?

input outputsomething happens

feedback

soundlouder sound

amplifier

feedback

The output feeds back to the input

Courtesy Don Perovich, CRREL

Ice-Albedo Feedback

ocean absorbs

more heat

more ocean

exposed

sea ice melts

warming

Positive feedback:more ice melt leads to more ice melt

Also works the other way:less ice melt leads to less ice melt

Operates every summer,with or without global warming

Need not lead to “runaway” situation

Notz (2009), PNAS, 106, #49, 20590–20595

Ice Growth Feedback

Thin ice grows faster than thick ice

thick icethin ice

Positive feedbackOutput is enhanced

Negative feedbackOutput is retarded

same thickness by late winter

Ice growth feedbackSummer:

Warming makes ice thinnerWinter:

Thin ice grows thicker faster

positive or negative

feedback?

?

?

?

?

Linear surface warming trend in °C per century from NCAR CCSM3 averaged from 9 ensemble members using the SRES A1B scenario

http://www.realclimate.org/index.php/archives/2006/01/polar-amplification/ courtesy of Cecilia Bitz, University of Washington

Arctic Amplification

Overland et al.

Is Arctic Amplification due to the Ice-Albedo Feedback?

IAF is not the whole story:

• AA occurs even with no IAF (in climate models)

• AA occurs even on an aqua planet (in models)

• Pole-ward heat and moisture transport are factors

Area of research… see: Processes and impacts of Arctic Amplification, Serreze and Barry, Global and Planetary Change 2011, 77, 85-96

Steele et al.

Tipping Points and Hysteresish

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X = 0 X = 1 X = 2

Final state

Initial state

0

2

Tipping Point:Where a small change in a parameter leads to a different equilibrium state

Hysteresis:The system follows a different path when the forcing is reversed

Climate Change, Sea Ice Loss, and Polar Bears in GreenlandKristin Laidre and Harry Stern, University of Washington, Seattle

Kristin April 2012

Track polar bear movements

Monitor sea ice at bear locations

Bear movements sea ice relation?

Movement behavior of adult male and female polar bears (Ursus maritimus) during the spring breeding season

Laidre et al. (2012) submitted

Polar bears use sea ice as a platform for hunting seals

Polar bears are found all across Baffin Bay in winter

Sea Ice in Baffin Bay, 1979-2011

1982-1991

1992-2001

2002-2011

Changes in Dates of Spring and Fallas defined by threshold in sea ice area

Spring transition

Fall transition

Length of summer

Draw best-fit lines

Are there trends?TO DO NOW

Also: Correlation of residuals = −0.64

Earlier spring tends to be followed by later fall

Ice-Albedo feedback??? Other explanations?

Changes in Dates of Spring and Fallas defined by threshold in sea ice area

+5 days/dec

+12 days/dec

−7 days/dec