Arctic sea ice next summer may shrink below the record low last year and it's hard to see how it won't eventually melt away completely, according to a University of Washington climatologist.
Speaking at the Alaska Forum on the Environment, Ignatius Rigor said global warming combined with natural cyclical changes likely will continue to push ice into the North Atlantic Ocean.
The last remnants of thick, old sea ice are dispersing and the unusual weather cycles that contributed to sea ice loss last year are continuing, he said.
"The buoys are streaming out," Rigor said, referring to the markers used to monitor the flushing of ice into the North Atlantic.
Scientists are watching Arctic sea ice closely, trying to sort out the effects of global warming and natural cyclical changes.
Formal projections of sea ice loss will be made for another month or so but all indications are that ice loss will equal or exceed last year's "unless the winds turn around," Rigor said.
New ice now covering the polar seas is not like older, thicker sea ice that once covered the region in winter, Rigor said. In 1989, 80 percent of the ice in the Arctic was at least 10 years old, he said. Today, only about 3 percent of the ice is that old.
New ice melts more quickly, and then open water absorbs more sunlight, warming the seas and making the fall freeze-up come even later, he said.
"Have we passed the tipping point?" he asked. "It's hard to see how the system may come back."
The prospect of a mostly ice-free Arctic could mean a boom in shipping through the Bering Strait, several speakers said, but is bad news for polar bears and other animals.
Bad news for bears
Polar bears prefer ice over the shallow continental shelf north of Alaska because it supports a rich food chain, said Steve Amstrup, a leading polar bear biologist with the U.S. Geological Survey. With melting last summer, some Alaska bears were on ice as much as 600 miles north of Barrow, far from their preferred habitat, Amstrup said.
Amstrup was lead federal biologist in studies released last year depicting the Alaska bear as likely to disappear by 2050 because of global warming. A decision by the Department of the Interior on whether to list the polar bear as "threatened" under the Endangered Species Act was due in January but has been postponed.
The state of Alaska, among others, opposes the listing, arguing the forecasts of declining sea ice are too speculative.
Scientists said that the forecasts were, if anything, too cautious. None foresaw the shrinkage of 2007.
"Five of the 10 studies we used projected more sea ice at mid-century than we had this summer," Amstrup said.
The shrinkage is related to higher temperatures, scientists said, but also to shifts in a weather pattern known as the Arctic oscillation. When the Arctic oscillation is in a "high" cycle, as it has been recently, more ice is pushed past Greenland into the North Atlantic, Rigor said.
Climate models have linked a higher Arctic oscillation to increases in greenhouse gases, but that relationship is the subject of much study, Rigor said.
"All these changes are very consistent with a climate system trying to cool itself off from greenhouse gases," Rigor said.