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Arctic Ice Levels at Record Low, May Keep Melting, Study Warns

Stefan Lovgren
for National Geographic News
October 3, 2005
 
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.

Record-Low Levels

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 extent—or the area of ocean that is covered by at least 15 percent ice—had 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.

The Arctic region may be particularly vulnerable to global warming. The average air temperatures in the Arctic between January and August of this year were 3.6° to 5.4°F (2° to 3°C) warmer than the average temperatures for that same period over the last 50 years.

Feedback Effect

Records show that global temperatures have increased 1°F (0.6°C) in the past century. Most scientists attribute this warming to human activities such as burning fossil fuels.

Researchers warn that the sea ice decline may contribute to even higher Arctic temperatures in the future. While bright ice reflects much of the sun's radiation, dark open water absorbs most of the heat from the sun, making the ocean warmer.

"That means when we get to the next winter we don't get as much growth of ice," Serreze said. "That means it will melt out even easier the next spring. By the end of the summer, you got even more of this open water area, absorbing even more solar energy. As the ocean gets more heat put into it, you have even less ice growth next winter, and so on."

Serreze says the satellite observations are consistent with climate models that predict the sea ice will continue to decline as the Arctic heats up. Some conservative computer models suggest there will be no summer sea ice in the Arctic by the year 2100.

Rising Waters, Shrinking Habitats

Global warming could lead to a rise in sea levels due to thermal expansion—as water heats up, it expands—and the melting of above-sea level glaciers. If the Greenland Ice Sheet, the largest ice mass in the Northern Hemisphere, were to melt completely, ocean levels would rise 22 feet (7 meters), scientists say.

Melting sea ice may lead to greater coastal erosion, because Arctic storms could produce much larger waves on the open ocean.

Several remote villages in Siberia and Alaska have already been evacuated due to coastal erosion.

As the sea ice continues to melt, polar habitat also continues to shrink.

"Much of the polar bears' livelihood is [based on] access to that sea ice," Serreze said. "There are some projections that within a century polar bears could be extinct."

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