Decline in Winter Arctic Ice Linked to Greenhouse Gases
Thursday, September 14, 2006
The amount of ice being formed in the Arctic winter has declined sharply in the past two years, a finding that NASA climate researchers say significantly increases their confidence that greenhouse gases created by autos and industry are warming the Arctic and the globe.
For years, scientists have reported a steady decrease in summertime Arctic ice, but they had never before found a similar reduction in the amount of ice being created during the frigid and dark Arctic winter. This lack of effect on the Arctic winter was one flaw in the scientific models of global warming, which predicted a steady decrease in ice formation.
But a new paper by Josefino Comiso, a senior research scientist at NASA's Goddard Space Flight Center in Greenbelt, found precisely the reduction in wintertime ice over the past two years that the model had predicted. The past two winters each produced 6 percent less ice than the average amount measured for almost three decades.
"This amount of Arctic sea ice reduction the past two consecutive winters has not taken place before during the 27 years satellite data has been available," Comiso said. "In the past, sea ice reduction in winter was significantly lower per decade compared to summer sea ice retreat. What's remarkable is that we've witnessed sea ice reduction at 6 percent per year over just the last two winters, most likely a result of warming due to greenhouse gases."
Comiso yesterday called the new data from satellite imaging of ice formation and temperatures "the strongest evidence of global warming in the Arctic so far."
The drop in wintertime ice tracks a similar drop in sea ice detected in the warmer months. According to Mark Serreze, senior research analyst with the National Snow and Ice Data Center, the amount of ice in the Arctic at the end of the 2005 summer was the smallest seen in 27 years of satellite imaging, and probably the smallest in 100 years. He said this year's summer ice cover started out even smaller but is not another record.
Serreze, in a teleconference with Comiso yesterday, said the new information on wintertime ice increases his confidence that greenhouse gases, and not other variables of weather and climate, are causing the warming.
"There a growing consistency here, with our observations in line with what our models project," said Serreze, whose group is part of the University of Colorado and does contract work for NASA.
Comiso said that researchers had been puzzled that wintertime ice creation remained robust in the Arctic while summertime melt was increasing, since the greenhouse effect would have potentially greater impact on wintertime ice.
In a paper that will appear in the journal Geophysical Research Letters, Comiso describes a "remarkable turn of events, with the observation of record low ice extent and area during the winters of 2005 and 2006." He adds: "The abnormally low winter ice maximum extent and area and enhanced surface temperatures in 2005 and 2006 . . . may just be the beginning of these trends which have been more apparent in other seasons."
Comiso said the wintertime polar warming may be caused by increases and changes in long-wave radiation from the sun, which is associated with the greenhouse effect. He also said the fact that there is so much less ice visible during the summer suggests that the ice cover is not getting as thick in the winter as it used to.
NASA also announced yesterday a study of the effects of shrinking Arctic ice formation on polar bears. The paper, to be published in the journal Arctic, found a marked decrease in the time that polar bears can spend on sea ice, their preferred platform for hunting seals and other sea mammals. As the coastal ice melts, said Claire Parkinson, a senior scientist at the Goddard facility, the animals have been forced to spend more time on land -- resulting in more encounters with people and a decline in the bears' average body weight.
The paper reports that the average weight of adult female polar bears in western Hudson Bay was 650 pounds in 1980. Their average weight in 2004 was 507 pounds -- a 143-pound drop.
"A key result of our research is its strong suggestion that climate warming is having a significant and negative effect on a primary species reliant on the sea ice cover for survival," Parkinson said.
She said that while the Antarctic experienced a sharp decline in ice cover during the 1970s but then recovered, there were no signs that the Arctic will now recover its ice in the same way.