The drastic melting of Arctic sea ice has finally ended for the year, scientists announced Wednesday, but not before demolishing the previous recordand setting off new warnings about the rapid pace of change in the region.
The apparent low point for 2012 was reached last Sunday, according to the National Snow and Ice Data Center, which said that sea ice that day covered about 1.32 million square miles, or 24 percent, of the surface of the Arctic Ocean.
When satellite tracking began in the late 1970s, sea ice at its lowest point in the summer typically covered about half the Arctic Ocean, but it has been declining in fits and starts over the decades.
The Arctic is the Earths air-conditioner, said Walt Meier, a research scientist at the snow and ice center, an agency sponsored by the government. Were losing that. Its not just that polar bears might go extinct, or that native communities might have to adapt, which were already seeingthere are larger climate effects.
His agency waited a few days before announcing the low to be sure sea ice had started to refreeze, as it usually does at this time of year, when winter closes in rapidly in the high Arctic. A shell of ice will cover much of the Arctic Ocean in coming months, but it is likely to be thin and prone to melting when summer returns.
Scientists consider the rapid warming of the region to be a consequence of the human release of greenhouse gases, and they see the melting as an early warning of big changes to come in the rest of the world.
Some of them also think the collapse of Arctic sea ice has already started to alter atmospheric patterns in the Northern Hemisphere, contributing to greater extremes of weather in the US and other countries, but that case is not considered proven.
The sea ice is declining much faster than had been predicted in the last big UN report on the state of the climate, published in 2007. The most sophisticated computer analyses for that report suggested that the ice would not disappear before the middle of this century, if then.
Scientists said Wednesday that the Arctic has become a prime example of the built-in conservatism of their climate forecasts. As dire as their warnings about the long-term consequences of heat-trapping emissions have been, many of them fear they may still