What Global Warming Might Mean for Extreme Snowfalls

Also, because of global warming, the air contains more moisture, on average, resulting in the possibility of heavier snowfalls when the temperature is conducive to snow.

http://www.climatecentral.org/news/global-warming-extreme-snowfall-17947

By Andrea Thompson
Aug. 27, 2014

So if the world is warming, that means winters should be less snowy, right? Well, it’s a bit more complicated than that. OK, it’s a lot more complicated.

While the average annual snowfall in most parts of the world is indeed expected to decline, the extreme snowfalls — those that hit a place once every 10 or 20 years and can cause major headaches and economic impacts — may decline at a slower rate, and could even increase in particularly cold places, a new study detailed in the Aug. 28 issue of the journal Nature finds.

Essentially, in a warming world, there are “more muted changes in [the intensity of] snowfall extremes than in average snowfall,” said study author Paul O’Gorman, a climate researcher at MIT.

The definition of extreme snowfall of course depends on where you are: For Boston, where O’Gorman lives and works, an extreme snow event might dump a couple feet of snow on the city, but “what’s extreme for Atlanta would be quite different,” he told Climate Central. “It really depends on where you are.”

Because the amount of feet in an extreme snowfall would be so dependent on the place, O’Gorman defined extremes by return times, so storms that happen only once every decade or two, which takes subjective snow depths out of the equation.

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The reason the change in intensity of extreme snowfalls seems to behave differently than the overall snowfall picture has to do with the physics that govern the formation of extreme snows. It seems that intense snows develop in a very narrow band of temperatures — it has to be cold enough that the precipitation won’t fall as rain, but can’t be so cold that the air doesn’t have enough moisture in it to fuel a blizzard.

In contrast, the snow that combines to give the annual total encompasses a much broader range of snow types that form under a wider swath of temperatures and so are more affected by warming. Essentially, in some places, less warming is needed to eat away at the temperature range that produces all snow than just the small range that accounts for extreme snows.

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One caveat is that in particularly mild regions that already don’t see much snowfall, a sufficient amount of warming could knock out both the extremes and the average, O’Gorman said. (On the opposite end, places that are cold enough could actually see an increase in extreme snowfalls.)

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