Recently, the north-eastern United States has had to contend with all manner of scary-sounding winter phenomenon like “bomb cyclones” and “thundersnow”. In fact, the last winter has been so devastatingly cold that frozen iguanas have been spotted dropping from trees and ice-covered sharks have washed up on Massachusetts beaches. So it was not exactly that big of a surprise when a certain climate-skeptic president sent this particular prize-winning tweet:
Yet, sadly, this extreme cold weather is probably not an anomaly. A study published in Nature Communications this week has linked the severely frigid climate of the north-eastern US to a warming Arctic and – yes – climate change.
Researchers from Rutgers University found that an abnormally warm Arctic raises the probability of extreme winter weather in the eastern US two to fourfold. It is also associated with below-average temperatures in northern Europe and Asia.
"Five of the past six winters have brought persistent cold to the eastern U.S. and warm, dry conditions to the West, while the Arctic has been off-the-charts warm," Jennifer Francis, research professor of marine and coastal sciences in Rutgers' School of Environmental and Biological Sciences, explained in a statement.
"Our study suggests that this is no coincidence.”
To reach this conclusion, the team worked out the Accumulated Winter Season Severity Index (AWSSI) across 12 US cities between 1950 and 2016, a tool that essentially measures the levels of extreme snowfall and temperatures at any given site. They then compared the data to anomalies in pan-Arctic geopotential heights and temperatures across the same period.
The results also suggest the connection between Arctic temperatures and severe winter weather was stronger when warming extended into the stratosphere, as opposed to being limited to surface level.
It's worth mentioning the study was observational, meaning the connection is correlational rather than cause and effect. Unfortunately, it is very hard to prove without a doubt that Arctic warming causes this extreme weather. This is because it is impossible to manipulate the variables (in this case, the temperature and geopotential heights in the Arctic), a limitation the researchers point out themselves.
It is also difficult to say what might be causing this correlation, but it could have something to do with the jet stream.
"Warm temperatures in the Arctic cause the jet stream to take these wild swings, and when it swings farther south, that causes cold air to reach farther south,” Francis added.
“These swings tend to hang around for a while, so the weather we have in the eastern United States, whether it's cold or warm, tends to stay with us longer."
While the study has not been without criticism, it does highlight the complexity of climate change. A rise in average global temperatures does not mean warmer weather across the board, a point some people may need reminding of.