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article imageGlobal warming ‘loading the dice’ for year-round extreme storms

By Lynn Herrmann     Mar 2, 2011 in Environment
Washington - This season’s extreme winter weather across much of North America and Europe, the result of global warming “loading the dice,” could be a prelude to future extreme storms in all seasons, a group of scientists said on Tuesday.
In a press release from the Union of Concerned Scientists (UCS) on Tuesday, a panel of scientists note this winter’s heavy snowstorms could be the norm for several decades as a warming planet reaches the point where heavy snowfalls will no longer occur.
“Heavy snowstorms are not inconsistent with a warming planet,” said Jeff Masters, director of meteorology for the Weather Underground website, the UCS release notes. “In fact, as the Earth gets warmer and more moisture gets absorbed into the atmosphere, we are steadily loading the dice in favor of more extreme storms in all seasons, capable of causing greater impacts on society,” he added.
The northeastern US experienced three snowstorms in each of the last two winters that qualified as Category 3 storms on the Northeast Snowfall Impact Scale (NESIS). This has only happened once in the last 50 years, during the winter of 1960-61.
According to the UCS release:
This winter and last, New York City experienced its two snowiest months on record—February 2010 (36.9 inches) and January 2011 (36 inches)—and Philadelphia experienced four of the top 10 snowstorms in its history. In the Midwest, Chicago was hit by its third biggest snowstorm on record early this February and Minnesota, South Dakota and North Dakota all have suffered through near-record snows this winter.
NESIS was developed in 2004 by Paul Kocin and Louis Uccellini of the National Weather Service to characterize and rank high-impact snowstorms in the northeastern US. High-impact storms deliver 10 inch snowfalls or greater and are ranked in five categories: extreme, crippling, major, significant, and notable.
“If the climate continues to warm, we should expect an increase in heavy snow events for a few decades, until the climate grows so warm that we pass the point where it’s too warm for it to snow heavily,” Masters added, UCS notes.
Mark Serreze, director of Boulder, Colorado’s National Snow and Ice Data Center, said the warming trends under way have had a noticeable impact on the Arctic region this winter. According to UCS, Serreze pointed out that winter temperatures this year have been at near record highs and the area covered by sea ice had shrunk to record low levels in December, January and February.
Serreze noted that less sea ice could lead to other global warming impacts, notably a strong negative phase of the Arctic Oscillation, the atmospheric circulation pattern in polar regions. Higher than normal atmospheric pressure occurs during the negative phase, resulting in wind patterns delivering warmer than average temperatures to the Arctic. In turn, cold Arctic air is forced down to middle latitude in Europe and the US.
“It’s still cutting edge research and there’s no smoking gun, but there’s evidence that with less sea ice, you put a lot of heat from the ocean into the atmosphere, and the circulation of the atmosphere responds to that. We’ve seen a tendency for autumns with low sea ice cover to be followed by a negative Arctic Oscillation,” Serreze said in the UCS release.
Reuters reports that this year’s heavy snowfalls in the midwest and northeastern US have dumped up to 400 percent of average snowfalls in certain locations. The amount of water in the accumulated snowpack is rated as some of the highest on record.
If you were to take all that water and melt it, it would come out to more than 6 inches over large swaths of the area,” Masters said, according to Reuters. “If all that water gets unleashed in a hurry, in a sudden warming, and some heavy rains in the area, we could be looking at record flooding along the Upper Mississippi River and the Red River in North Dakota,” he added.
Another phenomenon that may be linked to global warming is spring creep, a condition where spring thaws begin increasingly earlier.
“We’re also experiencing spring creep, where the warmer than average temperatures are shortening the length of winter,” Masters said, UCS notes. “For instance, we’re now seeing spring runoff in the mountains in the western U.S. starting one to three weeks earlier than 60 years ago.”
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