Antarctica is warming up

While the weather has been cold in some places over the past few months, the year 2008 was among the ten warmest years in the period of instrumental measurements, which extends back to 1880.  The ten warmest years all occur within the 12-year period 1997-2008.

Long term temperature trends courtesy NASA Goddard Institute for Space Studies.

Antarctica is warming up too, according to a new study led by Eric Steig, professor of Earth and space sciences at University of Washington. Some had thought Antarctica was kept cool by the ozone hole over the South Pole. Steig agrees that the ozone hole has contributed to some cooling in East Antarctica. "However, it seems to have been assumed that the ozone hole was affecting the entire continent, when there wasn't any evidence to support that idea, or even any theory to support it," he adds.

The new study shows that Antarctic surface temperatures increased an average of 0.22°F (0.12°C) per decade between 1957 and 2006. That's a rise of more than 1°F (0.5°C) in the last half century. West Antarctica warmed at a higher rate, rising 0.31°F (0.17°C) per decade. The results, published Jan. 22 in Nature, confirm earlier findings based on limited weather station data and ice cores.

While some areas of East Antarctica have been cooling in recent decades, the longer 50-year trend depicts that, on average, temperatures are rising across the continent. Antarctica contains 70% of the freshwater on Earth and some 90% of the world's ice, enough to raise world sea levels by 57 meters (187 ft), so even a tiny amount of melting could threaten coastal cities from Beijing to London.

The Intergovernmental Panel on Climate Change (IPCC), according to a Reuters report, thought that Antarctica would not contribute at all to sea level rise, and in fact predicted a growth of the big ice sheet that covers much of the continent from enhanced precipitation, resulting from increased evaporation from the oceans due to global warming. However, this enhanced precipitation has not eventuated in Antarctica.

Perhaps most troubling is that "a fairly large part of West Antarctica is warming more than we realized," says study co-author Michael Mann, a climatologist at Pennsylvania State University. West Antarctica is particularly vulnerable to climate changes because its ice sheet is grounded below sea level and surrounded by floating ice shelves. If the West Antarctic ice sheet completely melted, global sea level could rise by 20 feet (6.1 metres). In 2001, the IPCC said that collapse of this ice sheet was unlikely during the 21st century. As said before, this assessment now seems rather conservative.

West Antarctica "will eventually melt if warming like this continues," said Drew Shindell, of the NASA Goddard Institute for Space Studies, who was one of the authors. A 3 Celsius (5.4 F) rise could trigger a wide melt of West Antarctica, he said.

Greenland is also vulnerable. Together, Greenland and West Antarctica hold enough ice to raise sea levels by 14 meters. "Even losing a fraction of both would cause a few meters this century, with disastrous consequences," said Barry Brook, director of climate change research at the University of Adelaide in Australia.

Links:

Global Temperature Trends: 2008 Annual Summation - NASA

Satellites Confirm Half-Century of West Antarctic Warming - NASA

Antarctica is warming, not cooling: study - Reuters

Antarctica lost more ice in last 10 years: study - Reuters

Antarctica not immune to warming - USA Today

Dangers of Global Warming - update - by Sam Carana

Antarctic ice shelf collapse - by Sam Carana