How is the Polar Vortex Linked to Climate Change? – Treehugger
For the Central and Eastern United States, this has been a particularly brutal winter. Fargo, North Dakota has seen sub-zero temperatures since February 5, The Washington Post reported, while New York City has gotten hit with around 22 inches of snow since Jan. 31.
And it isn’t letting up any time soon. The National Oceanic and Atmospheric Administration (NOAA) predicts that temperatures in many parts of the lower 48 states will be 25 to 45 degrees below normal through Wednesday and that many places will see record lows before that date. The cold has extended as far south as Texas. Over the weekend and into Monday, an “unprecedented” winter storm has left millions without power in Texas and is creating chaos across a wide path of the central and southern states due to what the National Weather Service has called an “impressive onslaught of wicked wintry weather.”
Climate deniers have often used cold winter weather to argue against the idea that industrial society is heating the planet through the burning of fossil fuels. In one infamous example, Sen. James Inhofe (R-OK) brought a snowball onto the Senate floor to argue against the reality of global warming.
Such arguments fundamentally confuse weather (temporary fluctuations) and climate (long-term trends). But, counterintuitively, extreme wintry weather can actually be a sign of climate change.
For one thing, a warmer atmosphere holds more moisture, which makes heavy precipitation more likely. When the temperature is cold enough, that precipitation can fall as snow instead of rain.
“If you can get a moisture source and these storms come through, they are more likely to have more intense precipitation,” Dr. Brenda Ekwurzel, director of climate science and a senior climate scientist at the Union of Concerned Scientists, told Treehugger in an interview.
The other reason is more complicated and involves the phenomenon forecasters have come to refer to as the polar vortex.
The Polar Vortex Descends
Normally, the polar vortex swirls from west to east in the stratosphere above the Earth’s poles, keeping cold air over the Arctic and Antarctica. At the same time, the jet stream also circulates, keeping warm air to its south and cold air to its north.
Sometimes in the winter, the Arctic stratosphere will heat up through an event known as a Sudden Stratospheric Warming (SSW). This causes the winds keeping the polar vortex in place to weaken or even reverse, which in turn weakens the jet stream, making it wavier. The cold Arctic air is then brought down into the mid-latitudes.
“Sometimes we use the analogy of when you open up a refrigerator door,” Ekwurzel explained, “and the cold air that’s in the refrigerator, that’s contained in there, escapes, and then the warm air in the room goes into the refrigerator.”
So what does this have to do with climate change? The polar vortex itself is not a new phenomenon, and NOAA says the term likely originated in 1853. But the Arctic has been warming two to three times faster than the rest of the planet on average, and a growing body of observational research links this Arctic warming with extreme winter weather in Eurasia and North America, which has in fact increased in the past two decades.
A 2018 paper found that extreme cold and snowfall in the eastern U.S. were more common when the Arctic was warmest. Another 2020 study found that the melting of sea ice in the Barents and Kara Seas was associated with a weaker polar vortex in mid-January to late-February, which was typically displaced over Eurasia. At the same time, sea ice melt near Greenland and eastern Canada was associated with a weaker polar vortex from December to early February, that was displaced over Europe.
This trend is a problem for both the U.S. and Europe, and the Arctic itself. So far this winter, the mid-latitudes have seen three major disruptions, Ekwurzel explained.
- In December, a historic nor’easter coincided with record Siberian high temperatures, which was followed by record snowfall in Madrid in early January.
- In late January, another nor’easter blasted the northeastern U.S., breaking a 113-year-old snowfall record in one Pennsylvania town.
- The current descent of the polar vortex over much of the lower 48 states, accompanied by similarly cold temperatures in Europe.
However, these types of swings have negative consequences in the far North as well, where warmer than average temperatures make it harder for communities who rely on sea ice and snowpack for hunting and transportation. Ekwurzel used to study the Arctic ocean, and, during that time, heard stories of people who had crossed an icy river to hunt Caribou only to be stranded on the other side when it melted unexpectedly.
“No matter where you are in the Northern hemisphere, the extreme temperatures are disrupting your normal life and what you’re used to on a scale that wasn’t possible before,” Ekwurzel said.
There is some debate within the scientific community as to whether warmer Arctic temperatures are really causing cold weather events further south, or whether they are merely both occurring at the same time. One reason is that climate models do not show as strong a relationship between the two events, if they show one at all.
“The main reason for the disagreement among climate scientists is because the observations are strongly suggestive of a causal link and the models suggest there is no link. If the models validated or confirmed the arguments put forth by analysing the observations, there would be greater consensus,” atmospheric scientist Judah Cohen said in a Carbon Brief Q&A explaining the debate.
However, Ekwurzel said that models had also failed to predict the extent of Arctic warming. The problem is that it is a challenge for scientists to accurately model a climate that is so rapidly changing, meaning it is possible their models may have missed an important factor.
“The past is not our guide to the future, or today,” Ekwurzel said.