"Heavy snowstorms are not inconsistent with a warming planet," said Dr. Jeff Masters, director of meteorology and co-founder of the Weather Underground website. "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."
Snowstorm in Minneapolis, Minnesota, February 21, 2011 (Photo by Andy Tucker)
There are more heavy snowfalls still to come this winter and the Upper Midwest should be prepared for record flooding in the spring, Masters warned.
"One or two major snowstorms are expected to hit the Upper Midwest next week," he said. "They already have piled up snow pack there that's among the wettest on record and that threatens to unleash what could be record floods in Minnesota, South Dakota and North Dakota this spring."
"We're also experiencing spring creep, where the warmer than average temperatures are shortening the length of winter," Masters said. "For instance, we're now seeing spring runoff in the mountains in the western United States starting one to three weeks earlier than 60 years ago."
Todd Sanford, a climate scientist with the Union of Concerned Scientists said, "Think of atmosphere as a sponge.Two things happen: more water evaporates from the oceans. At the same time as atmosphere warms, it's able to hold more water vapor. That means that when we squeeze water out of sponge during storms, we're seeing it as much heavier precipitation events.
"Record low levels of sea ice in the Arctic affect atmospheric circulation patterns, causing the extreme winter weather we've been seeing. In the future, said Sanford, we can expect very heavy snowfalls, spring creep and the threat of serious flooding.
Masters said that in each of the past two winters the northeastern United States has had three snowstorms of Category 3 or higher on the Northeast Snowfall Impact Scale, which happened only once before in the past 50 years, during the winter of 1960-1961.
Snow storm in New York City, January 26, 2011 (Photo by Juan Jose Richards Echeverria)
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 had four of the top 10 snowstorms in its history.
In the Midwest, Chicago was hit by its third biggest snowstorm on record in February, while Minnesota, South Dakota and North Dakota all have had near-record snows this winter.
While sections of the United States have experienced stretches of unusually cold weather this winter, temperatures have not been much below average. That, too, provides an explanation for the heavy snowfalls.
"The old adage, ‘It's too cold to snow,' has some truth to it," said Masters. "A colder atmosphere holds less moisture, limiting the snowfall that can occur."
He cited a study documenting that 80 percent of all snowstorms in the United States of more than six inches during the 20th century occurred during winters with above average temperatures.
"If the climate continues to warm we should expect an increase in heavy snowstorms for a few decades," Masters said. "But eventually, with winters getting shorter, we may reach the point where it's too warm to snow heavily."
Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colorado, said, "It seems sometimes people's memories go back only as far as the latest cold snap or latest storm. People ask, 'Where's the global warming?' Well it's still here."
Dr. Serreze, who has been studying the Arctic climate since the early 1980s, said temperatures there have been near record high levels this winter. The area covered with sea ice shrank to record low levels for December 2010 through February 2011.
Arctic sea ice melts in the summer sun, July 2006 (Photo by Iowa Eyes)
Less sea ice means more moisture in the atmosphere, said Serreze, and it affects global weather in other ways.
For the second winter in a row, he explained, scientists have seen an unusually strong negative phase of the Arctic Oscillation, an atmospheric circulation pattern in polar regions.
During a negative phase, when atmospheric pressure is higher than normal in the Arctic, wind patterns bring warmer than average temperatures to the Arctic, while colder air spills down into the middle latitudes in the U.S. and Europe.
Recent research suggests that the low levels of sea ice could be a factor in causing negative Arctic Oscillation, Serreze said.
"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."
The only factor that can explain the climate change we are seeing is "radiative forcing due to rising greenhouse gas levels," said Serreze, although he acknowledged that it is "very hard to nail this down" and climate scientists are still learning.
For instance, the 2001 review of the world's scientific studies conducted by the Intergovernmental Panel on Climate Change concludes that milder winters will decrease, not increase, heavy snowstorms, a conclusion that is at odds with what Masters said Tuesday.
Masters responded, "Research is still being done, we don't have all the answers. Not necessarily all the research going on now will agree with what I said - that we expect more heavy snowstorms. Will next IPCC report modify conclusions from 2001? It will be interesting to see."
Said Serreze, "Scientists have learned since then. Climate science is a constantly evolving field, we continue to refine our ideas."
Copyright Environment News Service (ENS) 2011. All rights reserved.