Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations

TLDR

Rapid retreat and thinning of Arctic sea ice over recent decades is a striking sign of global climate change, with observed September extent declines exceeding CMIP3 model projections. CMIP5 models align better with observed satellite‑era trends yet still underestimate the decline, with 16 % of ensemble members showing no significant change, leaving uncertainty about when the Arctic will become seasonally ice‑free.

Abstract

The rapid retreat and thinning of the Arctic sea ice cover over the past several decades is one of the most striking manifestations of global climate change. Previous research revealed that the observed downward trend in September ice extent exceeded simulated trends from most models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3). We show here that as a group, simulated trends from the models contributing to CMIP5 are more consistent with observations over the satellite era (1979–2011). Trends from most ensemble members and models nevertheless remain smaller than the observed value. Pointing to strong impacts of internal climate variability, 16% of the ensemble member trends over the satellite era are statistically indistinguishable from zero. Results from the CMIP5 models do not appear to have appreciably reduced uncertainty as to when a seasonally ice‐free Arctic Ocean will be realized.