Arctic perennial sea ice -- the kind that stays frozen year-round -- declined by 14 percent between 2004 and 2005, climate scientists said Wednesday, in what one expert saw as a clear sign of greenhouse warming.
WASHINGTON Arctic perennial sea ice -- the kind that stays frozen year-round -- declined by 14 percent between 2004 and 2005, climate scientists said Wednesday, in what one expert saw as a clear sign of greenhouse warming.
Researchers have been monitoring the shrinking polar ice cap with satellites since the 1970s. What is new, and remarkable to scientists, is that the decline has been observed in winter as well as summer.
"The greenhouse phenomenon is actually becoming apparent in the Arctic," said Josefino Comiso of NASA's Goddard Space Flight Center outside Washington DC. "The winter warming signal is finally coming out."
Perennial sea ice used to be fairly stable in the Arctic, with declines of about 1.5 percent to 2 percent per decade, Comiso said in a telephone news conference. But in 2005 and 2006, this perennial ice was 6 percent smaller than the average amount over the past 26 years.
Another NASA team based at the Jet Propulsion Laboratory in Pasadena, California, used a satellite to calculate that Arctic perennial sea ice shrank by 14 percent between 2004 and 2005.
Summer sea ice has also declined dramatically in recent years, but 2006 is unlikely to eclipse 2005's record for summer ice-melt at the top of the world because of the cooling effects of a particularly stormy August, said Mark Serreze of the National Snow and Ice Data Center in Boulder, Colorado.
September is the month when sea ice is at its lowest ebb in the Arctic, making it a good time to gauge the health of the system of freezing and melting around the North Pole.
"What we're seeing now is that the health of the system is not particularly good," Serreze said.
WARMING THE ARCTIC
A satellite image taken on Monday showed Arctic sea ice shrinking away from its normal summer boundaries. One image showed a strange big hole in the summer ice north of Alaska. The hole, called a polynya, is probably about the size of the state of Maryland. Such a feature has never been seen in this area before, Serreze said.
Shrinking Arctic ice means less sunlight gets reflected and more gets absorbed, exacerbating the problem of warming. It also threatens Arctic species, notably polar bears, said Claire Parkinson, a research scientist at the Goddard center.
The polar bear population in Canada's Hudson Bay has dropped from 1,200 in 1989 to about 950 in 2004, a decline of 22 percent, Parkinson said at the teleconference.
Polar bears typically hunt on Arctic ice, but when ice is depleted, they will forage on land, she said. This has led to more sightings in Inuit settlements, but does not mean that the number of polar bears is increasing.
Most scientists believe global warming is due in some measure to the greenhouse effect, which occurs when so-called greenhouse gases are emitted into the atmosphere. These gases trap in Earth's heat like the glass walls of a greenhouse. Greenhouse gases, especially carbon dioxide, are byproducts of the burning of fossil fuels.
Environmentalists saw this research as more evidence of human-generated greenhouse emissions.
"It is not too late to save the Arctic, but it requires that we begin to slow carbon dioxide emissions this decade," James Hansen, director of NASA's Goddard Institute for Space Studies in New York, said in a statement.