When the Arctic is unusually warm, extreme winter weather is two to four times more likely in the eastern United States, according to new research. It is too early to say whether Arctic warming is causing these severe episodes of cold and, if so, how exactly. But the study shows how global climate change can have dominant effects at the local level, close to home.
The researchers analyzed a variety of atmospheric data in the Arctic, as well as how severe the winter weather was in 12 US cities. UU From 1950 to 2016. Since 1990, when the Arctic was warming and losing ice, extreme snaps of cold and heavy snow in the winter have been two to four times more frequent in the eastern United States and the Midwest, while that in the western United States, its frequency has decreased, according to a study published today in Nature Communications. The study, however, only shows that there could be a correlation, not a direct causal relationship, between Arctic warming and severe winters in the US. UU And it does not show how exactly the two are connected, so it does not really add much to what scientists already knew, according to several experts.
"In the real world, it's really hard to untangle cause and effect."
The Arctic is heating up at an unprecedented rate, and the sea ice is melting. At the same time, extremely cold clicks and heavy snowfalls have increased in North America, Europe and Asia. So, there is an energetic debate in the climate science community about how, if it does, the changing Arctic can be leading to these extreme weather in the Northern Hemisphere. It is also not clear whether the increase in extreme winter weather is simply happening naturally or due to climate change. Today's document does not show that the Arctic is responsible, so it does not put the debate to rest, say some experts.
"It's not the first document and it will not be the last to link the warm Arctic to the cold winters, but I'm still skeptical of that link," says James Screen, an associate professor of climate science at the University of Exeter, who was not involved. in the study. The mechanisms at play are still a mystery, and climate models do not really support this hypothesis, he tells The Verge. "This is based solely on observations – in the real world, it's really hard to unravel the cause and the effect."
Ted Shepherd, professor of climate science at the University of Reading, agrees. Observations alone are not sufficient to link extreme weather events with climate change, especially if they have been occurring in a regional area for a relatively short period of time. For that, you need models. "I do not think this document really helps to add new evidence to the table," Shepherd tells The Verge.
Only this year, the east of EE. UU It has seen record freezing temperatures, a "bomb cyclone" and three natural disasters in just 11 days, one of which brought severe flooding to Massachusetts. While the exceptional cold led to some, including the president of EE. UU., Donald Trump, to say that refutes global warming, scientists say that it is exactly the kind of climate expected in a warming world. And there are several mechanisms at play. For example, the increase in snowfall in the Northeast of the US UU And in the middle of the Atlantic it is partly due to warmer ocean temperatures and stronger coastal storms, which "produce stronger snowfalls than we have seen this season, with large total snowfalls", says Michael Mann, a climatologist and Director of the Earth System Science Center at Pennsylvania State University, in an email to The Verge.
"Cold air has to go somewhere, the question is where and what is the cause."
Today's study focuses on the Arctic as the main culprit in extreme winter weather. Previous research has suggested that warming the Arctic can interrupt the polar vortex, a swirling ring of cold air that surrounds the North Pole. Think of the polar vortex like a river, says study co-author Judah Cohen, a climatologist and director of seasonal forecasts at Atmospheric and Environmental Research. The rapid flow of this river blocks cold air over the Arctic. But as the Arctic warms up, especially in some areas like the Barents-Kara seas in northern Europe and Russia, a rock rises in this river, disrupting the polar vortex and allowing frozen arctic air to flow southward, says Cohen. (These cold explosions, for example, swept Europe last month, bringing snow to Rome for the first time in six years).
This same mechanism is what is causing extreme winter weather in the eastern United States. UU., According to Cohen. Today's study, however, only shows that there is a link between the changing Arctic and the severe cold periods in the US. UU., But it does not show that one causes the other. That link is "an obvious one," says Kevin Trenberth, a distinguished senior scientist at the National Center for Atmospheric Research, who was not involved in the research. "The cold air has to go somewhere, the question is where and what is the cause." Climate models do not confirm that Arctic warming is, in fact, driving these winter extremes in the US. UU., So there might be some other mechanisms at play, says Screen, at the University of Exeter. "Either the models are wrong, which is possible, or the interpretation of the correlation observed is incorrect," he says.
Cohen agrees that the investigation only shows correlation, not causation, and the document also recognizes it. As for the models, they are not very good at predicting winter weather in mid-latitudes. "Just as the observations are flawed, so are the models," Cohen tells The Verge.
The whole debate shows how much we still do not know about the complicated mechanisms by which climate change could wreak havoc on our planet. "It is unambiguous that the Arctic is warming and losing its sea ice, but people may ask," Why should I worry about that? ", Says Screen. The goal of today's study is to show that climate systems are interrelated, so changes in the Arctic could mean side effects elsewhere. "What happens in the Arctic does not stay in the Arctic," he says.