Arctic Sea Ice and the Ice-Albedo Feedback Harry Stern, Polar Science Center, University of Washington, Seattle Climate Complexity Workshop 2012 May 9, 2012

Arctic Geography

Greenland Alaska Canada Russia

Surface Area of the Earth LAND PACIFIC OCEAN ATLANTIC OCEAN INDIAN OCEAN ARCTIC OCEAN % 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 average sea ice concentration from satellite data National Snow and Ice Data Center (NSIDC), Boulder, CO

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Courtesy of NSIDC, Boulder, CO September Arctic Sea Ice Trends,

What is a Feedback? inputoutput something happens feedback sound louder 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 ice thin ice Positive feedback Output is enhanced Negative feedback Output is retarded same thickness by late winter Ice growth feedback Summer: Warming makes ice thinner Winter: 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 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, Steele et al.

Tipping Points and Hysteresis X = 0X = 1X = 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 Greenland Kristin 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,

Changes in Dates of Spring and Fall as 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 Fall as defined by threshold in sea ice area +5 days/dec +12 days/dec −7 days/dec