Arctic Sea Ice Melt Accelerating

BOULDER, Colorado, October 4, 2006 (ENS) - The Arctic Ocean will be ice-free by 2060 if current warming trends continue, scientists with the U.S. National Snow and Ice Data Center (NSIDC) said Tuesday. Measurements of Arctic sea ice from this year continued a pattern of sharp annual decreases due to rising temperatures, the researchers said, and the melting is consistent with predicted changes to the climate caused by rising greenhouse gas emissions.

"I'm not terribly optimistic about the future of the ice," said Mark Serreze, a research professor at the University of Colorado-Boulder's NSIDC. "Although it would come as no surprise to see some recovery of the sea ice in the next few years - such fluctuations are part of natural variability - the long-term trend seems increasingly clear. As greenhouse gases continue to rise, the Arctic will continue to lose its ice. You can't argue with the physics."

The melt is of concern to scientists because of its impact on ocean salinity and temperature, as well as its affect on Arctic wildlife.

"The loss of summer sea ice does not bode well for species like the polar bear, which depend on the ice for their livelihood," said CU-Boulder researcher Julienne Stroeve of NSIDC.

This image shows the average sea ice extent for the month of September; the magenta line indicates the average September sea ice extent from 1979 to 2000. 2006 had the second-lowest average September sea ice extent on record. (Photo courtesy NSIDC)

The research team used satellite data from NASA, NOAA and the U.S. Department of Defense, as well as data from Canadian satellites and weather observatories for the study.

The report is an annual look at the amount of sea ice at the close of the summer melting season, which typically ends around mid-September.

The amount of sea ice in 2006 was the second lowest on record.

The record low occurred last year, when the extent of sea ice was 20 percent lower than the average found from 1978 to 2001.

Only a change in weather prevented a new record from being set this year, the research team said.

"If fairly cool and stormy conditions hadn't appeared in August and slowed the rate of summer ice loss, I feel certain that 2006 would have surpassed last year's record low for September sea ice," said Serreze.

The pace of melting is also accelerating, the researchers report. Arctic sea ice melted at a rate of 6.5 percent per decade from 1979, when scientists first began official measurements, through 2001. That rose to 7.3 percent after 2002, reached 8 percent last year and is now at 8.6 percent - equivalent to 23.3 million square miles.

These latest measurements add to the concern that ice melt is accelerating due to a "positive feedback loop."

"Melting ice means more of the dark ocean is exposed, allowing it to absorb more of the sun's energy, further increasing air temperatures, ocean temperatures, and ice melt," explained CU-Boulder scientist Ted Scambos. "It seems that this feedback, which is a major reason for the pronounced effects of greenhouse warming in the arctic, is really starting to kick in."

The researchers found that average air temperatures across most of the Arctic Ocean from January 2006 to August 2006 were about 2 degrees to 7 degrees Fahrenheit warmer than the long-term average across the region over the past 50 years.

Ice extent from January to the middle of July 2006 was well below 2005 conditions and was consistent with the unusually warm air temperatures scientists have been tracking in the arctic in recent years, said Serreze.

High winter temperatures contributed to limited ice growth, and much of the ice that did form was thinner than normal.

"Unusually high temperatures through most of July then fostered rapid melt," Serreze explained. Cooler weather in August slowed the melt, he said, and storm conditions led to wind patterns that helped spread existing ice over a larger area.

But in September temperatures returned to above-normal patterns, which has meant a slow recovery from last month's minimum and indicates the sea ice extent this month could set a new record for the lowest October minimum.

The study is the latest in a slew of research documenting increased ice melt linked to global warming. (Photo courtesy NASA)

The researchers said one of the most notable features of the 2006 season was the development of a large polynya - an area of persistent open water surrounded by sea ice - that is visible north of Alaska

Calculations show that in early September, the polynya was the size of the state of Indiana, a huge feature never seen in the Arctic before.

Unusual wind patterns and an influx of warmer ocean waters may have caused the polynya to form, the researchers said.

The polynya is not directly attributable to greenhouse warming, according to the NSIDC team, but continued weakening and thinning of sea ice with increased warming could make such features more common in the future.