The Thinning of Arctic Sea Ice, 1988–2003: Have We Passed a Tipping Point?

TLDR

Recent satellite observations show record or near‑record lows in summer Arctic sea ice extent during 2002–05, and it is unclear whether this trend will continue or reverse with future cooling. The study aims to identify the physical processes responsible for the observed changes in Arctic pack ice by analyzing results from a regional coupled ice–ocean model. Using a regional coupled ice–ocean model, the authors hypothesize that thinning since 1988 results from gradual warming of fall‑winter‑spring air temperatures, a 1989 shift in the Arctic Oscillation and Pacific Decadal Oscillation that flushed older ice and expanded summer open water, and the resulting positive ice‑albedo feedback that amplifies melt. Model results indicate that basin‑wide ice thickness has thinned by 1.31 m (43 %) since 1988, most pronounced along the Chukchi‑Beaufort‑Greenland coast, with internal thermodynamic ice‑albedo feedbacks dominating the process and a tipping point in the late 1980s/early 1990s that continues to drive thinning even after climate indices normalize.

Abstract

Abstract Recent observations of summer Arctic sea ice over the satellite era show that record or near-record lows for the ice extent occurred in the years 2002–05. To determine the physical processes contributing to these changes in the Arctic pack ice, model results from a regional coupled ice–ocean model have been analyzed. Since 1988 the thickness of the simulated basinwide ice thinned by 1.31 m or 43%. The thinning is greatest along the coast in the sector from the Chukchi Sea to the Beaufort Sea to Greenland. It is hypothesized that the thinning since 1988 is due to preconditioning, a trigger, and positive feedbacks: 1) the fall, winter, and spring air temperatures over the Arctic Ocean have gradually increased over the last 50 yr, leading to reduced thickness of first-year ice at the start of summer; 2) a temporary shift, starting in 1989, of two principal climate indexes (the Arctic Oscillation and Pacific Decadal Oscillation) caused a flushing of some of the older, thicker ice out of the basin and an increase in the summer open water extent; and 3) the increasing amounts of summer open water allow for increasing absorption of solar radiation, which melts the ice, warms the water, and promotes creation of thinner first-year ice, ice that often entirely melts by the end of the subsequent summer. Internal thermodynamic changes related to the positive ice–albedo feedback, not external forcing, dominate the thinning processes over the last 16 yr. This feedback continues to drive the thinning after the climate indexes return to near-normal conditions in the late 1990s. The late 1980s and early 1990s could be considered a tipping point during which the ice–ocean system began to enter a new era of thinning ice and increasing summer open water because of positive feedbacks. It remains to be seen if this era will persist or if a sustained cooling period can reverse the processes.