Claire L. Parkinson
Sea ice is an integral component of the polar climate system, both affecting and responding to key processes in the polar oceans and atmosphere. In both polar regions, sea ice spreads over vast areas, with the wintertime sea ice areal extent in each hemisphere exceeding one and a half times the area of the US.
Both polar regions show considerable interannual variability, but both also show statistically significant trends in sea ice extent. The long-term trends have been greatest in the Arctic, where the annually averaged sea ice extent has been decreasing at a rate of about 3 per cent per decade. This equates to a loss, on average, of about 35,000-40,000 km2 of ice per year, a trend that will potentially have severe consequences on Arctic ecosystems should it continue. The Antarctic case, however, has been quite different, showing a sharp decline in the early and mid-1970s and an increasing trend of about 1 per cent per decade since then.
As the evidence for global warming and its impacts has accumulated, records of changes in sea ice have produced abundant data ripe for highlighting by both sides of the global warming debate. The Arctic sea ice decreases are firmly in line with the increasing Arctic temperatures, whereas the increases in Antarctic sea ice over the past quarter century are less easily placed in the global warming context.
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