Can natural variability explain observed Antarctic sea ice trends? New modeling evidence from CMIP5

Abstract

The recent observed positive trends in total Antarctic sea ice extent are at odds with the expectation of melting sea ice in a warming world. More problematic yet, climate models indicate that sea ice should decrease around Antarctica in response to both increasing greenhouse gases and stratospheric ozone depletion. The resolution of this puzzle, we suggest, may lie in the large natural variability of the coupled atmosphere-ocean-sea-ice system. Contrasting forced and control integrations from four state-of-the-art Coupled Model Intercomparison Project Phase 5 (CMIP5) models, we show that the observed Antarctic sea ice trend falls well within the distribution of trends arising naturally in the system, and that the forced response in the models is small compared to the natural variability. From this, we conclude that it may prove difficult to attribute the observed trends in total Antarctic sea ice to anthropogenic forcings, although some regional features might be easier to explain. Key Points Climate models exhibit large natural variability in Antarctic sea ice The observed trend in Antarctic sea ice falls within the natural variability The natural variability overwhelms the anthropogenic forcings ©2013. American Geophysical Union. All Rights Reserved.