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Author: Marlene Climons
Source: Climate Spectator
Date: 11 February, 2013 

As the Northeast digs out from under a mammoth blizzard, it might seem easy for climate change sceptics to point to such intense storms as evidence that global warming isn’t real.  

They would be wrong. 

“Climate change contrarians and deniers love to cherry-pick individual events to argue that they are somehow inconsistent with global warming, when they are not,” said Michael Mann, director of the Earth System Science Centre at Pennsylvania State University.  “As long as it’s cold enough to snow – which it will be in the winter – you potentially will get greater snowfalls.”

The reality is that such snowstorms often don’t occur despite global warming, but because of it. “It’s basic physics, and it’s irrefutable,” Mann said.  

Super-saturated air

The science behind this is clear: Warmer temperatures cause more water to evaporate into the atmosphere, and warmer air holds more water than cooler air. The air’s “water-holding capacity,” in fact, rises about 7 percent with each Celsius degree of warming. This results in air that becomes super-saturated with water, often bringing drenching rainfall followed by flooding or – if it is cold enough – heavy and intense snowfall. 

A study of 20th century snowstorms, published in the August 2006 Journal of Applied Meteorology and Climatology – before the big storms of recent years – found that most major snowstorms in the United States occurred during warmer-than-normal years. The authors predicted that “a warmer future climate will generate more winter storms.” 

True, warming temperatures are bringing us milder and shorter winters in most areas, including a later start to winter and earlier onset of spring. But we still are experiencing big snowstorms, especially in the northern part of the country. Climatologists predict that the coming decades will bring more of the same, meaning unusually warm winters, as well as potentially record-breaking blizzards.

It’s already happened in recent years. Few people will forget the monster snowstorms that walloped the Atlantic states in 2010, most notably a back-to-back punch only days apart in February that broke records in many major cities and, in Washington, D.C., became known as “Snowmageddon.” Rare storms also brought heavy snows to the deep South, including the northwest panhandle of Florida. In fact, by the second week of February, every state but Hawaii had snow on the ground.

The world is growing hotter due to human activities, among them the burning of fossil fuels like coal and oil, leading to dramatic increases of greenhouse gases, primarily carbon dioxide, in the atmosphere. These greenhouse gases absorb and radiate heat, and are reconfiguring the Earth’s climate.

The global average temperature since 1900 has risen by about 1.5 degrees Fahrenheit, and by 2100 is projected to rise another two to 10 degrees F, according to U.S. Global Change Research Program. The U.S. average temperature has risen by a comparable amount and is very likely to rise more than the global average over this century, with some variation from place to place, USGCRP says.

Shorter season

Paradoxically, winter, as a season, likely will become shorter as a result of increasing warming – potentially hurting winter recreation areas that depend on tourism – while snow, when it does fall, probably will be heavier. “Most likely we will see a shorter snow season, but more intense individual snowfall events,” Mann said.

Moreover,  the occasional snow storm likely will occur at odd times, such as October and April.  This already is happening.

“When you look at the seasonal cycle now, the biggest snow storms usually will be in fall and spring because the air is warmer and holds more moisture,” said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research. “There is a bigger chance for a big snowfall in late fall or early spring, and you will get more snow out of a given event.”

“You can still get snowstorms in mid-winter, but you can also get bigger snow amounts in fall and spring storms because the air is a little bit warmer than in mid-winter,” he said. “Winter still comes. We will still have cold snaps – but fewer of them.”  

Mann agrees that we are more likely to experience horrible snowstorms when the temperatures hover in the low 30s or high 20s Fahrenheit, rather than in the teens or colder. “There is something to that old saying: ‘It’s too cold to snow,”‘ he said.