The Arctic is heating up more than four times faster than the rate of global warming, according to a new analysis of observed temperatures.
The trend has stepped upward steeply twice in the last 50 years, a finding missed by all but four of 39 climate models, the researchers said.
The study does not pinpoint a cause for these relatively sudden increases, but the researchers speculate that contributing causes are probably sea ice and water vapour feedbacks combined with changes in how atmospheric and oceanic heat move into the Arctic.
"Thirty years is considered the minimum to represent climate change," said Petr Chylek, a physicist and climate researcher at Los Alamos National Laboratory, US, and lead author of the study published in the journal Geophysical Research Letters.
"We decreased the time interval to 21 years. At that smaller time scale, and contrary to previous investigations that found the Arctic amplification index increases in a smooth way, we observed two distinct steps, one in 1986 and a second one in 1999," Chylek said.