For years scientists have believed that one of the first signals of global warming would be the shrinking of the polar ice cover.
In today's edition of the British publication Nature, two scientist report a 2 percent decrease in the Arctic Ocean's ice cover between 1978 and 1987, discovered through a statistical analysis of satellite data.
While this record may be an indication of global warming, th scientists say their work is not conclusive evidence because it is a relatively short record.
"By itself, it is only a warning. It is not a definitive indicator," sai Per Gloersen, a senior scientist at NASA's Goddard Space Flight Center in Greenbelt. Dr. Gloersen said scientists would need 30 years of records to come up with a definitive conclusion.
Nevertheless, the work is likely to be viewed as one more piec of evidence that builds a case that the Earth's climate has started warming because of man's use of fossil fuels and "greenhouse" gases.
"There is an accumulation of results and pieces of evidence tha suggest something may be going on," said John E. Walsh, a scientist at the Department of Atmospheric Sciences at the University of Illinois at Urbana.
There is now scientific consensus that the average ai temperatures have increased by 1 degree Fahrenheit over the past century and that the level of carbon dioxide is on the rise.
How fast a warming will occur and how profoundly it will effec the Earth are still subjects of great debate in the scientific community.
The fact that the Arctic Ocean's ice cover is shrinking will no cause the level of the oceans to rise -- that would occur only if the continental ice sheets, such as those on Greenland, were to slide off.
But scientists have theorized that the shrinkage in the ocean' ice cover could cause an even faster warming on the Earth's surface because the ocean would absorb the light and heat that had been reflected by the ice cover.
In their analysis, Dr. Gloersen and William J. Campbell of the U.S Geological Survey's Ice and Climate Project at the University of Puget Sound found a large, seasonal fluctuation in the ice covers but an overall decrease.
They also found no change in the Antarctic ice cover.
The meaning of the new analysis was greeted with a good deal of skepticism by a colleague of Dr. Gloersen's at the National Aeronautics and Space Administration.
Claire Parkinson, a climatologist in the Oceans and Ice Branch at Goddard, said that records from the early 1970s seemed to indicate an 18 percent decrease in the Antarctic ice cover but that it was later reversed. "The problem for all of us in this field is we don't have nearly as long records as we would like to," she said.
However, Michael Oppenheimer, a scientist with the Environmental Defense Fund, said that such evidence is what would have been expected by those who have been predicting global warming and that it may indicate that the world is changing rapidly.
"We should get on with slowing down the changes," he said.