Arctic Sea Ice and the IceAlbedo Feedback Harry
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
Russia Alaska Canada Greenland
Surface Area of the Earth 40 30 36% 29% 18% 20 14% 10 3% 0 LAND PACIFIC OCEAN ATLANTIC OCEAN INDIAN OCEAN ARCTIC OCEAN
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
February
March
April
May
June
July
August
September
October
November
December
September Arctic Sea Ice Trends, 1979 -2011 Courtesy of NSIDC, Boulder, CO
What is a Feedback? input something happens output feedback sound amplifier feedback louder sound The outp feed u s ba t ck to th e inp ut
Ice-Albedo Feedback warming sea ice melts ocean absorbs more heat more ocean exposed Positive feedback: more ice melt leads to more ice melt Also works the other way: less ice melt leads to less ice melt Courtesy Don Perovich, CRREL Operates every summer, with or without global warming Need not lead to “runaway” situation
Ice Growth Feedback Thin ice grows faster than thick ice Positive feedback Output is enhanced Negative feedback Output is retarded Ice growth feedback Summer: Warming makes ice thinner Winter: Thin ice grows thicker faster thick ice thin ice same thickness by late winter ? ? positive or negative feedback? ? Notz (2009), PNAS, 106, #49, 20590– 20595 ?
Arctic Amplification Linear surface warming trend in °C per century from NCAR CCSM 3 averaged from 9 ensemble members using the SRES A 1 B scenario http: //www. realclimate. org/index. php/archives/2006/01/polar-amplification/ courtesy of Cecilia Bitz, University of Washington
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. Overland et al.
http: //www. ronmartin. net/blog/archives/2779 Tipping Points and Hysteresis Tipping Point: Where a small change in a parameter leads to a different equilibrium state X=0 X=1 2 Final state 0 Initial state X=2 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?
Polar bears use sea ice as a platform for hunting seals Polar bears are found all across Baffin Bay in winter Movement behavior of adult male and female polar bears (Ursus maritimus) during the spring breeding season Laidre et al. (2012) submitted
Sea Ice in Baffin Bay, 1979 -2011 1982 -1991 1992 -2001 2002 -2011
Changes in Dates of Spring and Fall as defined by threshold in sea ice area Fall transition Length of summer Spring transition TO DO NOW Draw best-fit lines Are there trends?
Changes in Dates of Spring and Fall as defined by threshold in sea ice area +5 days/dec +12 days/dec − 7 days/dec Also: Correlation of residuals = − 0. 64 Earlier spring tends to be followed by later fall Ice-Albedo feedback? ? ? Other explanations?
- Slides: 31