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Menopausal Mother Nature

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Climate ‘misperception’: Periods of extreme cold expected to … – Winston-Salem Journal

As residents of the Triad and much of North Carolina were buffeted by Arctic gusts expected to send wind chills below zero Friday, climate change likely was far from their minds.

In fact, deniers might be experiencing some holiday cheer, even as they shiver.

“Global warming, huh?” they may scoff while noting Triad temperatures more than 30 degrees below normal Friday.

The evidence is clear that most of the world is warming as human-generated greenhouse gases — primarily carbon dioxide — trap heat in the Earth’s atmosphere. Across much of the U.S., including North Carolina, winters are heating up faster than any other season.

On a decade-by-decade basis, the Triad’s annual average temperature in winter — commonly defined by weather scientists as December, January and February — has increased 4.5 degrees over the past 60 years, according to an analysis of National Weather Service data.

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Those averages have climbed consistently in every decade, with the biggest increase – 1.8 degrees – in the period from 2013 through last year

But counterintuitive as it may seem, the warming climate could actually drive an increasing number of Arctic weather systems into North Carolina, experts suggest. In fact, rising temperatures in the Arctic are likely fueling this phenomenon, they say.

Here’s how.

The polar jet stream — in the northernmost portion of Earth — and the subtropical jet stream are narrow bands of strong wind moving east to west at speeds that can top 275 mph. The flows follow the boundaries of hot and cold air, but not in straight lines.

High and low pressure systems, the positioning of warm and cold air, and seasonal changes alter the route of the streams.

“They meander around the globe, dipping and rising in altitude/latitude, splitting at times and forming eddies (swirls), and even disappearing altogether to appear somewhere else,” the National Weather Service explains.

As the Arctic gets warmer, the polar jet stream is slowing down, allowing it to meander even more, researchers say.

When the polar jet stream dips farther south, it brings frigid Arctic air with it, as it did Friday. That kind of jet stream variability could make the Southeast more susceptible to such cold extremes, even as winters continue to warm overall.

And while annual snowfall totals are falling in the Triad as temperatures rise, the same jet stream phenomenon could fuel more extreme single snow events, experts say.

“One misconception is that as winters warm, we won’t have any snow or cold days at all,” explains Corey Davis, assistant state climatologist at the N.C. State Climate Office. “While those are definitely becoming less frequent, in any given winter there is still plenty of cold air bottled up to our north, and if it dips far enough south, it can reach us and give us some pretty chilly and even snowy weather.”

John Deem covers climate change and the environment in the Triad and Northwest North Carolina. His work is funded by a grant from the 1Earth Fund and the Z. Smith Reynolds Foundation.

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