Extreme Winter Weather Linked To Climate Change

Deborah Zabarenko PlanetArk 2 Mar 11;

This winter's heavy snowfalls and other extreme storms could well be related to increased moisture in the air due to global climate change, a panel of scientists said on Tuesday.

This extra moisture is likely to bring on extraordinary flooding with the onset of spring in the Northern Hemisphere, as deep snowpack melts and expected heavy rains add to seasonal run-off, the scientists said in a telephone briefing.

As the planet warms up, more water from the oceans is evaporated into the atmosphere, said Todd Sanford, a climate scientist at the Union of Concerned Scientists. At the same time, because the atmosphere is warmer, it can hold onto more of the moisture that it takes in.

Intense storms are often the result when the atmosphere reaches its saturation point, Sanford said.

This year, a series of heavy storms over the U.S. Midwest to the Northeast have dropped up to 400 percent of average snows in some locations, said Jeff Masters, director of meteorology at Weather Underground.

The amount of water in that snowpack is among the highest on record, Masters said.

"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. "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."

That tallies with projections by the U.S. National Weather Service, which last month said a large stretch of the north central United States is at risk of moderate to major flooding this spring.

SPRING CREEP

Spring floods could be exacerbated by spring creep, a phenomenon where spring begins earlier than previously.

"We've documented in the mountains of the U.S. West that the spring runoff pulse now comes between one and three weeks earlier than it used to 60 years ago," Masters said. "And that's because of warmer temperatures tending to melt that snowpack earlier and earlier."

In the last century, global average temperatures have risen by 1.4 degrees Fahrenheit (.8 Celsius). Last year tied for the warmest in the modern record. One place this warmth showed up was in the Arctic, which is a major weather-maker for the Northern Hemisphere, according to Mark Serreze, director of the U.S. National Snow and Ice Data Center.

One driver of this winter's "crazy weather," Serreze said, is an atmospheric pattern known as the Arctic Oscillation, which has moved into what climate scientists call a negative phase.

This phase means there is high pressure over the Arctic and low pressure at mid-latitudes, which makes the Arctic zone relatively warm, but spills cold Arctic air southward to places like the U.S. Midwest and Northeast.

This negative Arctic Oscillation has been evident for two years in a row, the same two winters that have had extreme storms and heavy snowfalls.

It is possible, but not certain, that the negative Arctic Oscillation is linked to warming of the Arctic, which is in turn influenced by a decrease in sea ice cover throughout the region.

The only underlying explanation for these events is climate warming due to heightened greenhouse gas levels, Serreze said.

(Editing by Mohammad Zargham)

Global warming means more snowstorms: scientists
Yahoo News 2 Mar 11;

WASHINGTON (AFP) – Climate change is not only making the planet warmer, it is also making snowstorms stronger and more frequent, US scientists said on Tuesday.

"Heavy snowstorms are not inconsistent with a warming planet," said scientist Jeff Masters, as part of a conference call with reporters and colleagues convened by the Union of Concern Scientists.

"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."

Masters said that the northeastern United States has been coated in heavy snowfall from major Category Three storms or larger three times in each of the past two winters, storms that are unparalleled since the winter of 1960-61.

"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."

Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colorado, said less sea ice in the Artic translates to more moisture in the atmosphere, and could also cause an atmospheric circulation pattern in polar regions known as Arctic Oscillation.

"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," Serreze said.

"We've seen a tendency for autumns with low sea ice cover to be followed by a negative Arctic Oscillation."

Even though spring in North America is just around the corner, Masters said more snow is on the way next week in the upper Midwest, and the melting snow pack could spark record floods in Minnesota, South Dakota and North Dakota this spring.