WASHINGTON - With scant snowfall and barren ski slopes in parts of the Midwest and Northeast the past couple of years, some scientists have pointed to global warming as the culprit.
Then when a whopper of a blizzard smacked the Northeast with more than 2 feet of snow in some places earlier this month, some of the same people again blamed global warming.
How can that be? It's been a joke among skeptics, pointing to what seems to be a brazen contradiction.
But the answer lies in atmospheric physics. A warmer atmosphere can hold, and dump, more moisture, snow experts say. And two soon-to-be-published studies demonstrate how there can be more giant blizzards yet less snow overall each year. Projections say that's likely to continue with man-made global warming.
• The United States has been walloped by twice as many of the most extreme snowstorms in the past 50 years than in the previous 60 years, according to an upcoming study on extreme weather by leading federal and university climate scientists. This fits with a dramatic trend up in extreme winter precipitation in the Northeast charted by the National Climatic Data Center.
• Yet the Global Snow Lab at Rutgers University says spring snow cover in the Northern Hemisphere has shrunk on average by 1 million square miles in the last 45 years.
• And an upcoming study in the Journal of Climate says computer models predict that annual global snowfall will shrink by more than a foot in the next 50 years.
"Shorter snow season, less snow overall, but the occasional knockout punch," Princeton University climate scientist Michael Oppenheimer said. "That's the new world we live in."
Ten climate scientists say the idea of less snow and more blizzards makes sense: A warmer world is likely to decrease the overall amount of snow falling each year and shrink the snow season. But when it is cold enough for a snowstorm to hit, the slightly warmer air is often carrying more moisture, producing potentially historic blizzards.
"Strong snowstorms thrive on the ragged edge of temperature - warm enough for the air to hold lots of moisture, meaning lots of precipitation, but just cold enough for it to fall as snow," said Mark Serreze, director of the National Snow and Ice Data Center. "Increasingly, it seems that we're on that ragged edge."
Scientists won't blame a specific event or even a specific seasonal change on global warming without doing intricate, time-consuming studies. They are just now getting a better picture of the intersection of man-made climate change and extreme snowfall.
But when Serreze, Oppenheimer and others look at the last few years of less snow overall, punctuated by big storms, they say this is what they expect in the future.
"It fits the pattern that we expect to unfold," Oppenheimer said.
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