New satellite observations show that sea ice in the Arctic is melting faster while air temperatures in the region are rising sharply, scientists say.
Since 2002, satellite data has revealed unusually early springtime melting in areas north of Siberia and Alaska. Now the melting trend has spread throughout the Arctic, according to a national collaboration of scientists.
The latest observations through September show that melting in 2005 began a record 17 days earlier than usual.
The observations showed 5.27 million square kilometers of sea ice as late as September 19. It is the lowest measurement of Arctic sea ice cover ever recorded, researchers said, and 20 percent less than the average end-of-summer ice pack cover measurements recorded since 1978.
At the same time, average air temperatures across most of the Arctic region from January to August 2005 were as much as 2 C warmer than the average over the last 50 years, said the team of researchers from two universities and NASA.
"The melting and retreat trends are accelerating," Ted Scambos, of the University of Colorado at Boulder's National Snow and Ice Data Center (NSIDC), said in a statement released by the university. The results have not yet been published in a scientific journal.
"The one common thread," Scambos said, "is that Arctic temperatures over the ice, ocean and surrounding land have increased in recent decades."
The scientists stopped short of directly blaming the melting trend on global warming but said they have few other explanations at this point.
Mark Serreze, another researcher at the snow and ice data center, said: " I think the evidence is growing very, very strong that part of what we're seeing now is the increased greenhouse effect."
The researchers used satellite data from NASA, the National Oceanic and Atmospheric Administration and the Defense Department, as well as data from Canadian satellites and weather observatories.
The Colorado institute led the study that also involved two NASA laboratories, the National Oceanic and Atmospheric Administration and the University of Washington.
Sea ice records in the Arctic are sketchy before 1978. Since satellite observations began in earnest, researchers say Arctic ice has been retreating at a rate of more than 8 percent per decade.
If the shrinking trend continues at its present rate, there could be no ice at all at the pole as early as the summer of 2060.
And, they suspect, melting may only contribute to even higher arctic temperatures in the future. This is because the bright white ice tends to reflect more of the sun's radiation. With more of the dark ocean exposed, the seawater absorbs more heat, reducing the amount of solar energy reflected back into space.
As sea ice is already floating, it does not raise global sea levels when it melts. Changes in its extent, however, can have a major effect on the habitats of species such as polar bears.
"Polar bears must wait out the summer melt season on land, using their stored fat until they can return to the ice," Roger Barry, director of NSIDC, said, "but if winter recovery and sea ice extent continue to decline, how will these beasts survive?"
Chinese researchers also have a keen interest in sea ice in the Arctic.
"As the temperatures in the Arctic keep rising, the permanent frozen earth there is melting and shrinking to the north, thus narrowing animal and plant habitats," said Zhan Zhanhai, a sea ice expert and director of the Polar Research Institute of China.
"The retreating sea ice can disrupt the original climate system and affect weather in China," he said.
(China Daily September 30, 2005)