Antarctic climate change over the twenty first century

Here we present a new assessment of Antarctic climate change over the 21st century based on data from the models that were developed as part of the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4). To provide more reliable estimates of future change, a weighting scheme was applied to the model output, which depends on a measure of their ability to reproduce the mean climate of the late 20th century. The results show a seasonal variation of increases in circumpolar westerlies around Antarctica, which show the largest increases of 27% in autumn. This seasonal cycle was found to be consistent with projected changes in the semi-annual oscillation (SAO). In summer and autumn the increases of the westerly wind component migrate sufficiently far south to be manifested as a reduction of the coastal easterlies. The surface warming averaged over the continent is projected to be 0.34 degrees C dec(-1) with an inter-model standard deviation of 0.10 degrees C dec(-1). More rapid warming occurs during the winter over regions of sea ice retreat, e. g., 0.51 +/- 0.26 degrees C dec(-1) around East Antarctica. Projections of total sea-ice area show a decrease of 2.6 +/- 0.73 x 10(6) km(2) (33%). There is a projected increase of net precipitation averaged over the continent of 2.9 +/- 1.2 mm a(-1) dec(-1). The weighting gives a larger increase of the autumn SAO peak, up to 30% larger for April. This is consistent with larger weighted autumn increases of circumpolar westerlies, more sea ice reduction and resulting larger skin temperature increases.