I. Eisenman & J. S. Wettlaufer, PNAS, Nonlinear threshold behavior during the loss of Arctic sea ice

Proceedings of the National Academy of Sciences, Vol. 106, No. 1 (2009) 28-32; doi:10.1073/pnas.0806887106

Nonlinear threshold behavior during the loss of Arctic sea ice

I. Eisenman* (Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138) and J. S. Wettlaufer (Department of Geology and Geophysics and Department of Physics, Yale University, New Haven, CT 96520; and Nordic Institute for Theoretical Physics, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden)

1. Edited by Carl Wunsch, Massachusetts Institute of Technology, Cambridge, MA, and approved November 14, 2008 (received for review July 25, 2008)

Abstract

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.

• *To whom correspondence should be sent at the present address (Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 and Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195). e-mail: ian@gps.caltech.edu

• Author contributions: I.E. and J.S.W. designed research, performed research, and wrote the paper. The authors declare no conflict of interest.

• This article is a PNAS Direct Submission.

• This article contains supporting information online at www.pnas.org/cgi/content/full/0806887106/DCSupplemental.

• © 2008 by The National Academy of Sciences of the U.S.A.

Link to abstract: http://www.pnas.org/content/106/1/28.abstract

Link to full open-access article: http://www.pnas.org/content/106/1/28.full