1. Arctic Sea Ice and the Ice-Albedo Feedback
Harry Stern, Polar Science Center, University of Washington, Seattle
Climate Complexity Workshop 2012
May 9, 2012
21. What is a Feedback?
input output
something The
happens outp
feed u
s ba t
to th c
e in p k
ut
feedback
louder
sound sound
amplifier
feedback
22. Ice-Albedo Feedback warming
sea ice
melts
ocean more
absorbs ocean
more heat 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
23. Ice Growth Feedback Positive feedback
Output is enhanced
Thin ice grows faster than thick ice Negative feedback
Output is retarded
Ice growth feedback
Summer:
Warming makes ice thinner
Winter:
Thin ice grows thicker faster
thick ice same thickness
thin ice by late winter ?
? positive or
negative
feedback? ?
?
Notz (2009), PNAS, 106, #49, 20590–20595
24. Arctic Amplification
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
25. 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.
26. Tipping Points and Hysteresis
http://www.ronmartin.net/blog/archives/2779
Tipping Point:
Where a small change in
a parameter leads to a
different equilibrium state
Hysteresis:
The system follows a
different path when the
X=0 X=1 X=2 forcing is reversed
2
Final
state
0
Initial state
27. 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?
28. 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
29. Sea Ice in Baffin Bay, 1979-2011
1982-1991
1992-2001
2002-2011
30. Changes in Dates of Spring and Fall
as defined by threshold in sea ice area
Fall
transition
Length of
summer
Spring
transition
Draw best-fit lines
TO DO NOW Are there trends?
31. 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?