Insurance and Climate Change column

Is Climate Change Causing Colder Weather and More Snow in Eastern U.S.?

By | December 15, 2016

Baby, it’s cold outside.

And guess what? Climate change could make it even colder.

December’s a great time to talk about climate change and global warming – it’s cold and blustery across many parts of the U.S., and there’s even a bit of a chill in places like sunny Southern California.

Talking about global warming right now is sort of like yearning for a double-scoop ice cream cone dripping down your hand on a hot July day. Refreshing.

However, the consensus that a warming planet will lead us down a path of heatwaves, drought and more powerful storms, may be overly simplistic – in the eyes of one scientist, at least.

Judah Cohen, director of seasonal forecasting at AER, a Verisk Analytics business, believes things aren’t so simple.

He says that along with a warmer world, climate change may bring us more severe cold spells and more snow in certain areas.

Clearly Cohen is going against the grain of conventional thinking.

His assertion is based on his own findings that the Arctic may have a greater influence on the planet’s weather than is previously believed.

“I believe the Arctic is important in our weather, so I do consider that there’s a possibility, under the correct conditions, of an increase in extreme or severe winter weather,” Cohen said.

A warming of the Arctic region can actually lead to a disruption of the polar vortex and can bring colder weather south, according to Judah Cohen, director of seasonal forecasting at AER, a Verisk Analytics business.
A warming of the Arctic region can actually lead to a disruption of the polar vortex and can bring colder weather south, according to Judah Cohen, director of seasonal forecasting at AER, a Verisk Analytics business.

So, wait a minute, we can expect more cold weather because of climate change?

Before anyone cues the climate debate, Cohen is quick to add that his findings do not conflict with climate scientists who say the world is warming.

“Nothing in my papers or my ideas argues that the Earth shouldn’t continue to warm,” he said.

In his recent paper, “An observational analysis: Tropical relative to Arctic influence on midlatitude weather in the era of Arctic amplification,” Cohen argues that areas of the Eastern U.S., Europe and East Asia may be affected by warming in the Arctic.

The effect of that warming is more cold, and possibly more snow, in these areas during winter.

Climate science has long held that the Tropics exert the greatest influence on Earth’s climate system because they are the warmest, largest and most energetic region on the planet.

Climate change may produce more severe weather and a hotter planet, but temperature variations will be less severe, according to scientific consensus.

“All the conventional wisdom in the field has been about how we’re going to get this muted swing in temperature,” Cohen said.

In other words, a warming world, and a warming Arctic, should mean warmer weather and fewer cold extremes.

This graphic from Judah Cohen, director of seasonal forecasting at AER, shows that for two months in 1989-89 the polar vortex lies near the North Pole and it confines all the cold air around the Arctic. The polar vortex remains nearly perfectly round or circular and the contours show the flow of air remains west to east throughout the month.
This graphic from Judah Cohen, director of seasonal forecasting at AER, shows that for two months in 1989-89 the polar vortex lies near the North Pole and it confines all the cold air around the Arctic. The polar vortex remains nearly perfectly round or circular and the contours show the flow of air remains west to east throughout the month.
At the beginning of the animation based on a 2010 measurement, the polar vortex lies near the North Pole and it confines all the cold air around the Arctic, according to Cohen. As the animation advances in time, warm air emerges out of Siberia and shifts the polar vortex off the Pole and the polar vortex gets stretched out and elongated as cold air spills out from the Arctic into the mid-latitudes.
At the beginning of the animation based on a 2010 measurement, the polar vortex lies near the North Pole and it confines all the cold air around the Arctic, according to Cohen. As the animation advances in time, warm air emerges out of Siberia and shifts the polar vortex off the Pole and the polar vortex gets stretched out and elongated as cold air spills out from the Arctic into the midlatitudes.

But in his paper, Cohen shows that since 1990 to present we’ve gotten more extreme temperature swings.

Fuzzy logic applied to these perplexing swings includes the explanation that the Arctic air mass has just moved south.

“I think it’s overly simplistic to attribute cold extremes to some air mass that just moved from the Arctic into the midlatitude regions,” Cohen said.

Getting away from simplicity – far, far away – he described a “dynamic coupling” occurring with the polar vortex, which he said tends to weaken with accelerated Arctic warming.

“It’s not just a pure thermodynamic argument, but it’s a dynamic argument for these cold extremes,” he said.

Because of the world’s recent climate shifts, we’re experiencing a “weather whiplash,” or a series of extreme weather events worldwide, according to Cohen.

Feeling a bit lost?

The Eastern U.S. in the winter is sprung upon by the polar vortex – an upper level low-pressure area, beneath which lies a large mass of cold arctic air that’s positioned near the Earth’s poles.

A warming of the Arctic region can actually lead to a disruption of the polar vortex, like a dam bottled up over the Arctic just waiting to break, as Cohen explains it.

As Arctic warming increasingly disrupts the polar vortex, it begins to wobble, and the cold air in that dam spills out over lower latitudes, he said.

Think of the jet stream flowing west to east (with cold air to the north and warm to the south), where this is very little mixing of air masses.

This disruption essentially causes meandering, sending the jet stream on a north-south excursion.

“So there’s much more mixing of air mass,” Cohen said.

On the face of it, the thought that a warmer Arctic will bring colder weather to certain areas is counterintuitive. Cold air comes from the Arctic, so if you warm the Arctic then there should be less cold.

“If your bank account’s robbed, you’re not going to be able to take more money out of the ATM,” Cohen said. “But a warming Arctic can actually lead to this counterintuitive result.”

That result is definitely counterintuitive in the world of weather forecasters.

The Tropics and the El Niño/Southern Oscillation, or ENSO, are almost exclusively relied upon for seasonal forecasting. It is a less frequently considered and more controversial idea that Arctic variability is influencing midlatitude weather.

However, since the late 1980s and early 1990s, the Arctic has undergone rapid warming, referred to as Arctic amplification, which has coincided with an increase in extreme weather, according to Cohen’s paper.

“Analysis of observed trends in hemispheric circulation over the period of (Arctic amplification) more closely resembles variability associated with Arctic boundary forcings than with tropical forcing,” an abstract of Cohen’s paper states. “Furthermore, analysis of intraseasonal temperature variability shows that the cooling in midlatitude winter temperatures has been accompanied by an increase in temperature variability and not a decrease, popularly referred to as ‘weather whiplash.'”

Over this Arctic amplification period, climate extremes have even included cold air outbreaks and heavy snowfalls, most recently in North America and also in Eurasia over the past two decades, according to the paper.

These cold midlatitude winters have puzzled scientists.

Cohen’s research merely attempts to help solve the puzzle by putting the Arctic into the picture.

“The scientific community really has just focused on the Tropics.” Cohen said. “I think you expand that view and bring in the Arctic. The Arctic can also be influencing the weather here in the midlatitudes.”

He added, “Only if you include the Arctic does (this cooling trend) become reasonable.”

Cohen said his goal isn’t to provide commentary on whether the climate is changing –he believes it is, although he’s been accused of being both a climate change denier and a climate change apologist.

He’s just doing his job.

“I’m just trying to get a better understanding of what to anticipate during the coming winter,” he said.

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