September Arctic Sea Ice Trends, 1979-2011 Courtesy of NSIDC, Boulder, CO
What is a Feedback?input output something The happens outp feed u s ba t to th c e in p k ut feedback loudersound sound amplifier feedback
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 meltCourtesy Don Perovich, CRREL Operates every summer, with or without global warming Need not lead to “runaway” situation
Ice Growth Feedback Positive feedback Output is enhancedThin 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
Arctic AmplificationLinear surface warming trend in °C per century from NCAR CCSM3averaged from 9 ensemble members using the SRES A1B scenariohttp://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.
Tipping Points and Hysteresishttp://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
Climate Change, Sea Ice Loss, and Polar Bears in GreenlandKristin Laidre and Harry Stern, University of Washington, Seattle Kristin April 2012Track polar bear movementsMonitor sea ice at bear locationsBear movements sea ice relation?
Polar bears use sea ice asa platform for hunting sealsPolar bears are found allacross Baffin Bay in winterMovement behavior of adult male andfemale polar bears (Ursus maritimus)during the spring breeding seasonLaidre 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 Draw best-fit linesTO DO NOW 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/decAlso: Correlation of residuals = −0.64Earlier spring tends to be followed by later fallIce-Albedo feedback??? Other explanations?