for National Geographic News
The amount of sea ice in the Arctic shrank dramatically this summer and is now smaller than it has been in a century of record-keeping, new research reveals.
Scientists say rising temperatures brought on by human-made global warming is probably to blame for the melting trend.
If the decline in sea ice continues, summers in the Arctic could become completely ice-free before the end of this century, scientists warn.
The shift could lead to increased coastal erosion and shrinking habitat for animals like polar bears.
"We're going to see a dramatically different Arctic," said Mark Serreze, a research scientist at the National Snow and Ice Data Center in Boulder, Colorado. The center led the research, which also involved NASA, the National Oceanic and Atmospheric Administration, and the University of Washington.
Since 2002 satellite imagery has revealed strong melting north of Siberia and Alaska in the early springtime. According to the new research, however, the melting trend has now spread throughout the Arctic.
"In 2002 we were already flabbergasted at how little ice we had, but in the past four years the bottom has kind of dropped out of the system," Serreze said. "The difference in ice cover from 2002 to 2005 is roughly the size of Colorado."
Arctic sea ice builds up in the winter and melts in the summer, typically reaching its minimum in September. On September 21, the sea ice extentor the area of ocean that is covered by at least 15 percent icehad dropped to 2 million square miles (5.3 million square kilometers), the lowest ever observed during the satellite record, which dates back to 1978.
There are natural causes that may lead to the increased melting. Scientists believe that a circulation pattern in the atmosphere that pushes sea ice out of the Arctic region may have contributed to periodic ice reduction in the past.
But this pattern has not been an influence on the region since 1996, researchers say, and sea-ice decline has still continued to accelerate.
"The most fundamental thing that helps explain the loss of ice is that the Arctic is simply getting warmer," Serreze said.
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