Winter Arctic sea ice declining drastically

The amount of Arctic sea ice is shrinking not only in the summer but in the winter, as well, a NASA scientist reported on Wednesday. Researchers are linking the change directly to global warming.
In 2005 and 2006, the extent of winter ice was about 6% smaller than the average amount over the past 26 years. The retreat is also significantly larger than the long-term decrease of 1.5 to 2% in winter ice cover observed per decade over the same time period.
Researchers have long known that warmer temperatures have been causing more and more ice to melt during summer in the northern hemisphere, with the last four summers showing record lows in ice cover.
Now, Josefino Comiso of NASA’s Cryospheric Sciences Branch in Greenbelt, Maryland, US, has used satellite data stretching back to 1979 to show that less of the meltwater is refreezing in the wintertime.
“It is the strongest evidence yet in the Arctic of global warming,” Comiso said in a press conference on Wednesday.
Greenhouse warming
Mark Serreze, a senior research scientist for the US National Snow and Ice Data Center in Boulder, Colorado, who is not on the team, agrees.
"There is lots of natural climate variability – it is a complex science – but the best explanation of what we are seeing is the emerging signs of greenhouse warming,” he said. “What we see in the Arctic is a [dead] canary in the coal mine.”
“I hate to say we told you so,” Serreze said of predictions on global warming from the past five years, “but, we told you so.”
Comiso found that from 1979 to 2004, the extent of winter ice in the Arctic remained virtually the same – despite reductions in summer cover.
He believes the recent decline is due to a reduction in the length of the Arctic ice season and unusually warm wintertime temperatures in the region. Serreze agrees: “What is different this year is what is happening in winter."
“If the winter ice retreat continues, the effect could be very profound – especially for marine mammals,” Comiso says.
Polar bears, which rely on drifting ice to hunt seals, are believed to be hit especially hard by the diminishing icepack. In Canada’s Hudson Bay, the bears' population has dropped 21%, from an estimated 1200 individuals in 1989 to 950 in 2004, according to Claire Parkinson, also of NASA’s Cryospheric Sciences Branch.
Journal reference: Geophysical Research Letters (in press)