If I had a dime for every time during these last few snowstorms that some self-imagined wag has said, "Whatever happened to global warming?!" ...
The short response is that global warming doesn't mean it's getting warmer at every place on earth every minute. And that weather -- with all its daily anomalies -- is an entirely different matter from the broader realm of climate.
The more thorough answer comes from Brenda Ekwurzel, a climate scientist with the Union of Concerned Scientists.
“Climate change projections show that a warming planet generates more precipitation in areas that typically experience rain or snow,” Ekwurzel said in a press release from the science-based nonprofit. Large snowstorms are consistent with global warming because warmer air holds more moisture, she said. Rising ocean surface temperatures already have increased the temperature and moisture content of the air passing over the United States, setting the stage for heavier snow and rain storms. An Intergovernmental Panel on Climate Change report found that global warming has increased the frequency of storms that dump heavy precipitation over most land regions that experience storms. Most deserts, conversely, are getting drier.
“Climate scientists aren’t at all surprised that there are more blizzards in certain parts of the country,” said Ekwurzel. “That’s consistent with well-documented climate change trends over the past several decades.”
The press release goes on to say that precipitation in the Northeast has increased over the last century, according to the Northeast Climate Impact Assessment, a collaboration between UCS and a team of more than 50 scientists and economists. Over the past few decades, winter precipitation in the Northeast has increased 0.15 inch per decade.
William L. Chameides, dean of Duke University's Nicholas School of the Environment and a member of the National Academy of Sciences, also has weighed in. “There is a reason we call it global warming," he says in a press release from Duke. “Global temperatures can be warming even if temperatures in the United States are not.”
While we've been experiencing wintry extremes, other regions of the world -- including Australia, Brazil and south Africa -- have had to contend with extreme heat waves, he says.
Chameides says that even here in the U.S., this winter has been exceptional for its snow, but not its cold. The National Oceanic and Atmospheric Administration’s National Climate Data Center reported that January 2010 was the fourth-warmest January on record. Average temperatures in the contiguous United States that month were about a half a degree Fahrenheit above the long-term averages.
“This pattern of warmer temperatures and stronger storms is consistent with climate models that show global warming will bring more extreme weather, specifically more severe storms with greater amounts of precipitation,” Chameides says.
In other words -- back to the short version here -- it's very complicated, and not a matter of a snowstorm one day and a winter freeze the next.