WASHINGTON — This year will see the second-biggest loss on record of Arctic sea ice — a sign that the area of ice coverage is shrinking at a pace faster than once expected.
The trend also suggests that global warming is likely to increase, polar bear habitat will decline and previously icebound areas could be opened to oil and gas exploration.
Mark Serreze, a senior scientist at the National Snow and Ice Data Center, said Tuesday that the sea-ice minimum, which will be reached later this month, won't hit last year's record because the amount of daylight is decreasing in the Arctic and a new freeze is beginning.
But the minimum amount of ice at summer's end this year will be near last year's total. In 2007, the extent of Arctic ice was 23 percent lower than the previous record in 2005. That 2007 total, which set a record, was 1.65 million square miles. As of Monday, satellite observations showed 1.78 million square miles.
Arctic sea ice is important because it reflects most sunlight, keeping polar regions cool and producing a cooling effect at lower latitudes. Open water, in contrast, absorbs the sun's energy, and the warm ocean waters mean more ice melting, the National Snow and Ice Data Center says.
If ice is lost, more sun is absorbed, and heat from the ocean is released back to the atmosphere, Serreze said.
The understanding of the impacts of these changes is still in its infancy, Serreze said.
The center's measurements show the ice has declined dramatically during the past 30 years.
"The real issue is what's the long-term trend, and it's negative," said Serreze. He said summer could be ice-free in the Arctic by 2030. Some scientists give it just another decade.
Two years of extreme ice minimums indicate that the low in 2007 wasn't random, said James Overland, a scientist who researches the arctic climate at the National Oceanic and Atmospheric Administration (NOAA).
The cause of the ice loss is a combination of global warming from an increase of greenhouse gases and natural variations — winds that brought warm temperatures and blew ice to the Atlantic side, Overland said. If the cause was global warming alone, most scientists thought they wouldn't see this kind of ice loss for 30 years, he said.
This summer conditions were more normal in the Arctic, but the ice was thinner to begin with.
"The question was, would the new ice last through the summer — and it did not," Overland said.
The relationship between ice and ocean conditions will make it hard for sea ice to return to what it was before, he said. Instead, the long-term trend will be decline in ice cover.
Two years ago, scientists didn't foresee major sea ice loss until 2050, but because of a combination of factors, "we're on a fast track," Overland said.
Ignatius G. Rigor, a scientist who researches Arctic sea ice and the atmosphere at the Polar Ice Center at the University of Washington, said he still thinks there's a chance this year's minimum will hit a new low.
Rigor said greenhouse gases from fossil fuels are changing the climate, bringing warmer temperatures and changes in weather patterns over the long term.
Arctic sea ice is far below the average in the 1980s and before, and has been declining since about the 1970s, Rigor said. The ice retreat coincides with increasing temperatures around the globe.
Like Overland, Rigor said the changes in Arctic sea ice are from a combination of global warming and natural changes — winds, high pressure and higher temperatures. The bottom line, he said, is that temperatures are important, but variations in wind are also part of the equation.
Overland was one of the government scientists who determined that the polar bear should be listed as an endangered species because global warming would reduce sea ice by 2050.
In the past two years, polar bears north of Alaska and Siberia have had "a very difficult time," and that will continue for the foreseeable future, he said.
Sea ice habitat will decline to 20 percent of what it was 20 years ago, Overland said. When that will happen isn't known, but 2030 is a reasonable projection, he added.
Overland also said that declining ice also speeds up the prospects of oil exploration in northern Alaska, Canada and Siberia.
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