Nonlinear threshold behavior during the loss of Arctic sea ice

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Eisenman, I., Wettlaufer, J. S.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: National Academy of Sciences 2009
• Subjects: Arctic climate; bifurcation; climate change; tipping point; Arctic; Arctic Ocean; Keller; albedo; Climate change; Sea ice
• Online Access: https://doi.org/10.1073/pnas.0806887106; https://www.ncbi.nlm.nih.gov/pmc/PMC2629232

In light of the rapid recent retreat of Arctic sea ice, a number of studies have discussed the possibility of a critical threshold (or "tipping point") beyond which the ice–albedo feedback causes the ice cover to melt away in an irreversible process. The focus has typically been centered on the annual minimum (September) ice cover, which is often seen as particularly susceptible to destabilization by the ice–albedo feedback. Here, we examine the central physical processes associated with the transition from ice-covered to ice-free Arctic Ocean conditions. We show that although the ice–albedo feedback promotes the existence of multiple ice-cover states, the stabilizing thermodynamic effects of sea ice mitigate this when the Arctic Ocean is ice covered during a sufficiently large fraction of the year. These results suggest that critical threshold behavior is unlikely during the approach from current perennial sea-ice conditions to seasonally ice-free conditions. In a further warmed climate, however, we find that a critical threshold associated with the sudden loss of the remaining wintertime-only sea ice cover may be likely. © 2009 by The National Academy of Sciences of the USA. Edited by Carl Wunsch, Massachusetts Institute of Technology, Cambridge, MA, and approved November 14, 2008 (received for review July 25, 2008). Published online before print December 24, 2008, doi:10.1073/pnas.0806887106 We thank the Geophysical Fluid Dynamics summer program at Woods Hole Oceanographic Institution (WHOI) [National Science Foundation (NSF) Grant OCE0325296], where the development of the physical representations used in this study benefited from discussions with many visitors and staff including Norbert Untersteiner, John Walsh, Jamie Morison, Dick Moritz, Danny Feltham, Göran Björk, Bert Rudels, Doug Martinson, Andrew Fowler, George Veronis, Grae Worster, Neil Balmforth, Ed Spiegel, Joe Keller, and Alan Thorndike. I.E. thanks Eli Tziperman and Cecilia Bitz for helpful conversations during the course of this ...