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