This isn't a good old-fashioned winter for the District of Columbia, not unless you're remembering the last ice age. And it doesn't disprove global warming, despite Sen. Jim De Mint's cheerful tweet: "It's going to keep snowing until Al Gore cries 'uncle.' "

Instead, the weird and disruptive weather patterns around the world are pretty much exactly what you'd expect as the planet warms. Here's how it works: In most places, winter is clearly growing shorter and less intense. We can tell, because Arctic sea ice is melting, because the glaciers on Greenland are shrinking and because a thousand other signals send the same message.

But rising temperature is only one effect of climate change. Probably more crucially, warmer air holds more water vapor than cold air does. The increased evaporation from land and sea leads to more drought but also to more precipitation, since what goes up eventually comes down. The numbers aren't trivial -- global warming has added 4 percent more moisture to the atmosphere since 1970. That means that the number of "extreme events" such as downpours and floods has grown steadily; the most intense storms have increased by 20 percent across the United States in the past century.

So here's the thing: Despite global warming, it still gets cold enough to snow in the middle of winter. It even gets cold enough to snow in Texas and Georgia, as it did late last week. And the chances of what are technically called "big honking dumps" have increased. As Jeff Masters, the widely read weather blogger, pointed out last week, a record snowstorm requires a record amount of moisture in the air. "It is quite possible that the dice have been loaded in favor of more intense Nor'easters for the U.S. Mid-Atlantic and Northeast, thanks to the higher levels of moisture present in the air due to warmer global temperatures," he wrote.

The climatalogical climate is only part of the equation. The political climate counts, too -- and there's no question that it's harder to make legislative progress when Sen. James Inhofe's grandchildren are building an igloo next to the Capitol with a big sign that says "Al Gore's New Home." The timing here is particularly tough, for the snowstorms come against the backdrop of renewed attacks on the pillars of climate science -- charges that hacked e-mails show some researchers to be venal or that key scientists have financial ties to energy industries.

Looked at dispassionately, those political attacks essentially buttress the consensus around global warming. If that much money and attention can be aimed at the data and all anyone can find is a few mistakes and a collection of nasty e-mails, it's a pretty good sign that the science is sound (though not as good a sign as the melting Arctic). The British newspaper the Guardian just concluded a huge series on the "Climategate" e-mails with the words: "The world is still warming. Humanity is still to blame. And we still, urgently, need to do something about it."

Looked at dispassionately, the round of snowmageddons crisscrossing the mid-Atlantic carries the same message. But it's hard to be dispassionate when you're wondering, six hours of shoveling later, if there's a good chiropractor in the neighborhood and what kind of dogsled you might need to reach her.
It's almost like a test, centered on ground zero for climate-change legislation. Can you sit in a snowstorm and imagine a warming world? If you're a senator, can you come back to work and pass a bill that blunts the pace of climate change? If the answer is no, then we're really in a world of trouble.

Bill McKibben is a scholar in residence at Middlebury College and the co-founder of 350.org. He is the author of "The End of Nature" and the forthcoming "Earth: Making a Life on a Tough New Planet."

References
"Harsh Winter a Sign of Disruptive Climate Change, Report Says"

http://www.washingtonpost.com/wp-dyn/content/story/2010/02/12/ST2010021202631.html
By Juliet Eilperin and David A. Fahrenthold
Washington Post Staff Writer
Thursday, January 28, 2010

This winter's extreme weather -- with heavy snowfall in some places and unusually low temperatures -- is in fact a sign of how climate change disrupts long-standing patterns, according to a new report by the National Wildlife Federation:

Oddball Winter Weather: Global Warming's Wake-Up Call for the Northern Unites States
National Climatic Data Center
http://www.ncdc.noaa.gov/ussc/USSCAppController?action=snowfall_returnp&state=18&station=BALTIMORE%20WB%20AIRPORT&coopid=180465