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Home >> Sci-Edu
UPDATED: 09:23, September 29, 2005
Scientists say Arctic ice continues decline in warming climate
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A team of scientists said on Wednesday that extremely low summer sea-ice coverage in the Arctic continued in September 2005, which may be the result of warming temperatures and earlier spring melting.

This year could surpass 2002 as the lowest amount of sea-ice cover in more than a century, the researchers noted.

Satellite data from US space agency NASA revealed that unusually early springtime melting in areas north of Siberia and Alaska since 2002, and in 2005 the trend has expanded to include the entire Arctic ice pack, according to Ted Scambos of US National Snow and Ice Data Center.

The research group used satellite record dating back to 1978 to determine that the 2005 spring and summer melting began about 17 days earlier than usual, a new record.

Average air temperatures across most of the Arctic Ocean from January to August 2005 were between 2 and 3 degrees Celsius warmer than the average value of the past half-century, said the team.

The conditions were followed by the lowest sea-ice extent yet seen in the satellite data, a five-day mean average of 5 million square kilometers on Sept. 19. The team reported the extent was lower than the mean average September sea-ice extent from 1978 to 2001 by about 20 percent.

Since the 1990s, The melting and retreat trends are accelerating, and the one common thread is that Arctic temperatures over the ice, ocean and surrounding land have increased in recent decades, the researchers said.

The winter of 2004-2005 exhibited the smallest recovery of Arctic sea ice of any previous winter in the 23-year satellite record, the group reported. With the exception of May 2005, every month since November 2004 has exhibited the lowest monthly average of sea-ice extent since satellite record-keeping began in the region.

Although sea-ice records prior to 1978 are comparatively sparse, they imply the recent decline exceeds previous sea-ice lows, the researchers said.

Arctic sea ice typically reaches a minimum in September at the end of the summer melt season. The trend of Arctic sea ice decline documented by satellites is now about 8.4 percent per decade since the 1970s, the group reported.

Scientists believe the Arctic Oscillation, a major atmospheric circulation pattern that can push sea ice out of the Arctic, may have contributed to the sea-ice reduction in the mid-1990s by making it more vulnerable to summertime melt. While the pattern has become less of an influence on the region since the late 1990s, the sea ice has continued to decline.

The decline is likely to affect future temperatures in the Arctic, since ice acts as a cooling mechanism to reflect most of the sun's radiation back into space, Scambos said. As sea ice melts, larger areas of darker ocean decrease the amount of solar energy reflected away from Earth.

Arctic sea ice consists of both annual ice and multi-year ice. The multi-year ice has been declining at almost 10 percent per decade.

While a recovery of multi-year ice would require sustained cooling in the Arctic, especially during the summer months, climate models predict continued Arctic warming, the researchers said.

Source: Xinhua


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