Nonlinear threshold behavior during the loss of Arctic sea ice

TL;DR

This paper investigates the physical processes behind Arctic sea ice loss, showing that while multiple stable states exist, a critical threshold for sudden ice loss is unlikely under current conditions but possible in a warmed climate.

Contribution

It provides new insights into the nonlinear threshold behavior of Arctic sea ice, emphasizing the role of thermodynamic effects in stabilizing ice cover and identifying potential tipping points.

Findings

Multiple ice cover states are supported by ice-albedo feedback.

Thermodynamic effects stabilize the ice during most of the year.

A critical threshold for sudden winter ice loss may occur in a warmed climate.

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 while 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.