Climate change

Winter in Philadelphia can be snowy and cold, even with climate change


A month-long snow blitz was underway in Philadelphia, with up to 4 feet building up in nearby suburbs.

Texas, which has long suffered devastating and destructive hurricane damage, experienced an all-out disaster of a different kind, a cold snap that bypassed the state’s electricity grid and darkened millions of homes and companies.

At one point, nearly three-quarters of the contiguous United States was blanketed in snow during what turned out to be the coldest February in more than 30 years.

And with the 2021-22 snow season about to begin, northern hemisphere snow cover would be above normal in October and November if the trends continue.

READ MORE: Will it snow another day? Should we be worried? Yes and yes, says New Jersey’s international snow expert.

Is it global warming? Yes, say polar scientist Judah Cohen and other researchers, it is the work of climate change; more precisely, what they call “arctic change”.

In 2020, global temperatures were about 1.74 degrees Fahrenheit above the 20th century average, according to the National Centers for Environmental Prediction. The Arctic region has warmed twice as fast.

Rising temperatures this way melted snow and ice which in turn released previously frozen waters.

Changes in the vital cold air pantry of the northern hemisphere could conspire to disrupt the upper atmosphere in a way that causes powerful pulses of polar air to spread more frequently to lower latitudes via the polar vortex, say Cohen and his co-authors in an article published in the journal Science last month.

“I’m not saying winters are getting colder,” Cohen, of Atmospheric and Environmental Research Inc., said in a telephone interview. But climate models have generally underestimated the ferocity of winters, and “expecting harsh winter conditions to decrease could be dangerous.”

READ MORE: What went wrong for the Philly winter forecast? “The polar vortex stole the show.”

Other atmospheric scientists, like NOAA researcher Amy Butler, agree that the arctic heat may well be linked to severe winter episodes in the United States. However, they expressed reservations about the limited period of observations and said it was not clear whether the authors had identified a trend.

Between 10 and 30 miles above the surface, during the winter, the polar vortex circulates around the Arctic with winds sometimes exceeding 150 mph.

When it howls, it confines vast puddles of freezing air, perhaps 100 degrees below zero Fahrenheit, over the sunless North Pole. Don’t ask about wind chill.

Occasionally, disturbances at lower levels of the atmosphere disrupt the stratosphere so that the vortex weakens, exporting arctic air as it seeps south.

In a way that is not fully understood, the cold air of the upper atmosphere interacts with the low-level jet winds that ignite and carry winter storms.

With 40 years of observations, Cohen and his team conducted computer modeling experiments using previously identified arctic atmospheric pressure models that preceded the polar vortex disturbances.

They included data to simulate the loss of arctic sea ice and recent increases in autumn snow cover in Eurasia – which they attributed to the additional moisture available in the released waters. The modeling results strongly showed a “physical link” between the warming of the Arctic and the weakening of the polar vortex which leads to a spill of cold air, they wrote, resulting in severe winter epidemics in Philadelphia and elsewhere.

Butler, a researcher at NOAA’s Chemical Sciences Laboratory, said the team’s concept was more than exaggerated. Their “hypothesis is plausible,” she said, but “I don’t think there is convincing evidence of a long-term trend in the strength of the polar vortex.

But any change in its location or shape could also influence the weather, she said.

Paul Pastelok, the seasoned seasonal forecaster at AccuWeather Inc., said the team’s results were promising, but the data was limited.

“We need more precise measurements to go back to the 1960s,” he said. “We don’t have real data for the whole Arctic, only partially, and that’s just not enough.”

Nothing happens in a vacuum in the atmosphere, and Pastelok said he has no doubts that the Arctic has a powerful influence on winter conditions and low latitudes.

He said he was an admirer of Cohen’s articles, which included the correlation of October snow cover in Siberia with the North American winter that followed, and consulted them to expand on his outlook.

READ MORE: Winter forecast for Philly calls for early snowfall, cold December and 100% chance of uncertainty

Regarding the results of the Science article, Pastelok said, “I think it will take another 20 years to really determine whether or not this can be used as a forecasting tool.”

Cohen says they might come in handy in the short term. “I would say the Arctic can precondition the atmosphere for these events so that you can anticipate when such events are more likely over the coming winter,” he said.

And in the meantime, he argues that it would be a mistake to conclude that a warmer world will result in milder American winters.

See: Texas, February 2021.


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