The new analysis, published in the journal Communications Earth and Environment, starts 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 asking how the region is defined “is a very, very relevant conversation for understanding change in the Arctic.” A larger Arctic would include more land and reduce the impact of ice-ocean feedback on average temperatures.
dr Ballinger, who was not involved in either study, is the author of the annual Arctic Report Card that is produced for the National Oceanic and Atmospheric Administration. He said some of the findings from the Finnish study are particularly interesting, including those showing very high rates of warming in the late 1980s and 1990s. “That was really when Arctic amplification rates were at their strongest,” he said.
The earlier study, published in Geophysical Research Letters last month, looked at data from 1960 onwards and defined a larger Arctic north of the 65th parallel that includes more land. They found that the rate of warming has been four times the global average for about 20 years. And unlike the Finnish study, they found that there were two decades-long periods, from the mid-1980s to the mid-1990s and into the 2000s, of large warming jumps in the region.
“It’s not changing continuously, it’s changing incrementally,” said Manvendra K. Dubey, an atmospheric scientist at Los Alamos. And since they are decades-long periods, they suggest that natural climate variability as well as warming from increased greenhouse gas emissions from human activities were involved.
dr Rantanen said his group’s findings also suggest a role for natural variations in the rate of warming, perhaps some long-term changes in ocean or atmospheric circulation.