3 On thin ice?
Satellite radar altimeter measurements show that although the Antarctic ice sheet is growing overall at a modest rate, four coastal glaciers are rapidly thinning. The figure shows the relative changes in the heights of these glaciers with time, with the lines offset by an arbitrary amount for clarity. The growth in the size of the ice sheet is due to a short-term increase in snowfall, whereas the thinning is due to a longer-term acceleration of glacier flow triggered by warming oceans. If the amount of carbon dioxide doubles during the 21st century - as the Intergovernmental Panel on Climate Change assumes in one of its scenarios - Antarctic glacier losses will overtake projected snowfall gains by the year 2035. This, in turn, would lead to even bigger rises in sea levels.