Century-scale perspectives on observed and simulated Southern Ocean sea ice trends from 20th century ice core proxies.

Abstract:

The failure of coupled climate model ensembles to reproduce the increased Antarctic sea ice cover observed by satellites raises grave doubts about our ability to accurately predict the future of the Antarctic climate system, with important implications in the context of predicting Antarctica’s contribution to future sea level rise. While the increase in total Antarctic ice cover is within the bounds of coupled model internal variability, the spatially heterogeneous pattern of trends indicates that Antarctic sea ice may have a response to anthropogenic forcings that is not replicated by the models. A complete understanding of this discrepancy is hampered by the relatively short satellite record. In this work, 20^th century sea ice reconstructions from a number of ice cores are combined to give a synthesis covering about 75% of the circumpolar region. It is found that in sectors with the biggest SAM response, late winter sea ice cover has been decreasing since the 1960s, in qualitative agreement with CMIP5 models. In the Ross Sea the observed increase in ice cover has been a occurring since the mid 1960s, when it was preceded by a sharp, decade long reduction, outside the range of simulated natural variability.