Arctic Summer Sea Ice Shrinking Fast

BOULDER, Colorado, September 28, 2005 (ENS) - The extent of Arctic sea ice this summer is smaller than it has been since 2002, and federal government scientists say if current rates of decline in sea ice continue, the summertime Arctic could be completely free of ice before the end of this century.

Scientists from NASA and the National Snow and Ice Data Center today called this summer's ice reduction "stunning," and concluded that Arctic sea ice is likely on "an accelerating, long-term decline."

"Considering the record low amounts of sea ice this year leading up to the month of September, 2005 will almost certainly surpass 2002 as the lowest amount of ice cover in more than a century," said Julienne Stroeve of the National Snow and Ice Data Center (NSIDC) based in Boulder.

This decline in sea ice amounts to about 500,000 square miles, an area roughly equivalent to twice the size of Texas.

melt

Melting Arctic sea ice in a warming Arctic summer (Photo by Peter West courtesy National Science Foundation)
Arctic sea ice extent, or the area of ocean that is covered by at least 15 percent ice, typically reaches its minimum in September, at the end of the summer melt season. On September 21, the five-day running mean sea ice extent dropped to 5.32 million square kilometers (2.05 million square miles), the lowest extent ever observed since the satellite record began in 1978.

The current decline also exceeds past low ice periods in the 1930s and 1940s, the research team said.

For the period 1979 through 2001, before the recent series of low extents, the rate of September decline was slightly more than 6.5 percent per decade.

After the September 2002 minimum, the record low before this year, the trend steepened to 7.3 percent.

Incorporating the 2005 minimum, with a projection for ice growth in the last few days of September, the estimated decline in Arctic sea ice at the end of summer is now eight percent per decade.

All four years have ice extents about 20 percent less than the 1978 through 2000 average.

These findings confirm a report last month from University of Arizona geoscientist Jonathan Overpeck indicating that current warming trends in the Arctic may result in a seasonally ice free state not seen for more than one million years.

The entire Arctic is affected, not the North American Arctic alone.

In mid-September, NSIDC Director Roger Barry spent time in Russia's Laptev Sea on an Arctic icebreaker. The ship entered only one area of continuous ice to the east of Severniya Zemvya, one of the most northern island chains of Russia. Barry said that by comparison, "That whole area was covered in thick multiyear ice last year, in September of 2004."

The impact on Arctic animals will be a matter of life and death, Barry said. "We saw several polar bears quite close to the ship," he said. "Polar bears must wait out the summer melt season on land, using their stored fat until they can return to the ice. But if winter recovery and sea ice extent continue to decline, how will these beasts survive?"

With four consecutive years of low summer ice extent, scientists are more confident than ever that a long-term decline is underway. Walt Meier of NSIDC said, "Having four years in a row with such low ice extents has never been seen before in the satellite record. It clearly indicates a downward trend, not just a short-term anomaly."

Cooler winter temperatures allow the sea ice to "rebound" after summer melting. But last winter, the scientists documented the recovery of sea ice extent was the smallest in the satellite record.

bear

Polar bear swims in the Beaufort Sea. August 1978 (Photo courtesy NOAA)
With the exception of May 2005, every month since December 2004 has set a new record low ice extent for that month.

Explained NSIDC scientist Florence Fetterer, "Even if sea ice retreated a lot one summer, it would make a comeback the following winter, when temperatures fall well below freezing. But in the winter of 2004-2005, sea ice didn't approach the previous wintertime level."

Satellite records also reveal that since 2002 springtime melting is beginning unusually early in the areas north of Alaska and Siberia. The 2005 melt season arrived even earlier, beating the mean melt onset date by approximately 17 days, this time throughout the Arctic.

In addition, Arctic temperatures are rising. Compared to the past 50 years, average surface air temperatures from January through August, 2005, were two to three degrees Celsius (3.6 to 5.4 degrees Fahrenheit) warmer than average across most of the Arctic Ocean.

"The year 2005 puts an exclamation point on the pattern of Arctic warming we’ve seen in recent years," said Mark Serreze of NSIDC. "The sea ice cover seems to be rapidly changing and the best explanation for this is rising temperatures," Serreze said.

In earlier centuries, whole expeditions were lost as their crews tried to beat through thick ice and bitter cold of the legendary Northwest Passage through the Canadian Arctic from Europe to Asia.

This summer the Northwest Passage was completely open except for a 60 mile swath of scattered ice floes.

The Northeast Passage, north of the Siberian coast, was completely ice free from August 15 through September 28.

The trend in sea ice decline, lack of winter recovery, early onset of spring melting, and warmer-than-average temperatures suggest a system that is trapped in a loop of positive feedbacks, in which responses to inputs into the system cause it to shift even further away from normal. One of these positive feedbacks centers on increasingly warm temperatures.

Serreze explained that as sea ice declines because of warmer temperatures, the loss of ice is likely to lead to further ice losses.

melt

Watching the ice melt and break up on the north shore of Tigvariak Island, Alaska North Slope, summer 1949. Summer ice cover was low in the 1940s too, but the past four years are the lowest. (Photo by Rear Admiral Harley Nygren courtesy NOAA)
Sea ice reflects much of the Sun's radiation back into space, while dark ice free ocean absorbs more of the Sun's energy. As sea ice melts, Earth's overall albedo, the fraction of energy reflected away from the planet, decreases. The increased absorption of energy further warms the planet.

"Feedbacks in the system are starting to take hold," says NSIDC Lead Scientist Ted Scambos. Moreover, these feedbacks could change our estimate of the rate of decline of sea ice. "Right now, our projections for the future use a steady linear decline, but when feedbacks are involved the decline is not necessarily steady - it could pick up speed."

The Arctic system is large and complex, and there are many factors driving change in the region. For example, scientists believe that 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. However, the pattern has become less of an influence in the region since the late 1990s, and yet sea ice has continued to decline.

On his cruise north of Siberia, Barry saw another example of a factor that contributes to changes in the Arctic. "Warm water flowing from the Atlantic is persisting in the Siberian Arctic in a layer 100 to 400 meters (109 to 437 yards) below the surface," Barry said.

Heat is probably transferring upward from this layer, helping to maintain open water conditions, he theorizes.

Scientists point out that a longer record of data will continue to help them better examine, piece apart, and understand both the influences and the remarkable changes that they are now seeing.

Scientists who collaborated on this study work at the NASA Goddard Space Flight Center in Greenbelt, Maryland; the NASA Jet Propulsion Laboratory in Pasadena, California; NSIDC at the University of Colorado in Boulder, Colorado; and the University of Washington in Seattle, Washington.

Studies of arctic sea ice extent are funded by NASA and the National Oceanic and Atmospheric Administration (NOAA). In assessing present-day Arctic sea ice extent, researchers used data from NASA, NOAA, U.S. Department of Defense, and Canadian satellites and weather observing stations.