The warming at the top of the globe, a sign of climate change, is happening much faster than previously described compared with the global average, scientists said Thursday.
A definitive sign of climate change, the rapid warming of the Arctic, is occurring even faster than previously described, researchers in Finland said Thursday.
Over the past four decades the region has been heating up four times faster than the global average, not the commonly reported two to three times. And some parts of the region, notably the Barents Sea north of Norway and Russia, are warming up to seven times faster, they said.
While scientists have long knownthat the Arctic is warming rapidly the rate has been a source of some confusion, described in scientific reports and news accounts as anywhere from two to three times faster than the global average.
Mika Rantanen, a researcher at the Finnish Meteorological Institute in Helsinki, said he and his colleagues decided to look at the issue in the summer of 2020, when intense heat waves in the Siberian Arctic drew a lot of media attention.
“We were frustrated by the fact that there’s this saying that the Arctic is warming twice as fast as the globe,” Dr. Rantanen said. “But when you look at the data, you can easily see that it is close to four.”
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The new findings are bolstered by those of another recent study, led by scientists at Los Alamos National Laboratory, which found similar rates of warming, although over a different time span.
The greater warming has effects in the Arctic, including faster melting of the Greenland ice sheet, which leads to greater sea-level rise. But it also affects atmospheric circulation in North America and elsewhere, with impacts on weather like extreme rainfall and heat waves, although some of the impacts are a subject of debate among scientists.
The Arctic is heating more rapidly in large part because of a feedback loop in which warming melts sea ice in the region, which exposes more of the Arctic Ocean to sunlight and leads to more warming, which in turn leads to even more melting and warming. The result of this and other oceanic and atmospheric processes is called Arctic amplification.
How the rate of warming in the Arctic is described compared with the global average is related in part to the time period that is analyzed and how the region is defined.
The new analysis, published in the journal Communications Earth and Environment, begins with data from 1979, when accurate temperature estimates from satellite sensors first became available. The researchers also defined the Arctic as the area north of the Arctic Circle, above about 66 degrees latitude.
Thomas Ballinger, a researcher at the University of Alaska Fairbanks, said the issue of how the region is defined “is a very, very relevant conversation for understanding Arctic change.” A bigger Arctic would include more land, reducing the impact of the ice-ocean feedback on average temperatures.
Dr. Ballinger, who was not involved in either study, is an author of the annual Arctic Report Card prepared for the National Oceanic and Atmospheric Administration. He said some of the findings in the Finnish study were especially interesting, including those showing very high rates of warming in the late 1980s and 1990s. “That really was when Arctic amplification rates were the strongest,” he said.
The earlier study, published last month in Geophysical Research Letters, looked at data from 1960 onward and defined a larger Arctic, north of 65 degrees latitude, which includes more land. They found that the rate of warming reached four times the global average starting about 20 years ago. And unlike the Finnish study, they found that there were two decade-long periods, from the mid-1980s to the mid-1990s, and in the 2000s, with large jumps in warming in the region.
“It doesn’t change continuously, it changes in steps,” said Manvendra K. Dubey, an atmospheric scientist at Los Alamos. And because these are decade-long periods, they suggest that natural climate variability, as well as warming resulting from increased emissions of greenhouse gases from human activity, were involved.
Dr. Rantanen said his group’s results also suggest a role of natural variability in the rate of warming, perhaps some long-term changes in ocean or atmospheric circulation.
But clearly the sea ice-ocean interaction is most important, he said, especially in areas like the Barents Sea where the warming rate is even higher.
“The warming trends are quite strongly coupled with the decline of sea ice,” he said. “They’re most highest over those areas where the sea ice has been declining the most. That’s the primary reason.”
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