THE WALL STREET JOURNAL

Sea Ice Might Be More Resilient Than Thought

Single cool summer briefly reversed decline in ice cap around the North Pole, study reports

Arctic sea ice is so sensitive to changing temperatures that a single cool summer briefly reversed the decline in the ice cap around the North Pole, says a new study released Monday.

Using new satellite data, researchers at University College London reported in Nature Geoscience on Monday that the total volume of sea ice in the Northern Hemisphere was well above average in the autumn of 2013, traditionally the end of the annual melt season, after an unusually cool summer when temperatures dropped to levels not seen since the 1990s.

“We now know it can recover by a significant amount if the melting season is cut short,” said the study’s lead author Rachel Tilling, a researcher who studies satellite observations of the Arctic. “The sea ice might be a little more resilient than we thought.”

A steady decline in the extent of Arctic sea ice since the late 1970s has been taken as a barometer of longer-term warming trends in the Northern hemisphere. The U.S. Navy last year predicted that by 2030 the Arctic’s northern sea route could be ice-free and navigable for nine weeks every year.

Miss Tilling and her colleagues used new data from the European Space Agency’s Cryosat-2 radar satellite, launched in 2010. For the first time, they measured changes in the overall volume of seasonal sea ice across the Arctic and Greenland. Until now, researchers have been able to track the extent of ice, but not its thickness.

In 2013, summer temperatures were about 5% cooler than the previous year and the volume of autumn ice jumped 41%, they said.

As temperatures warmed again after 2013, the decline in annual sea ice resumed, according to the U.S. National Snow and Ice Data Center in Boulder, Colo. At its greatest expanse this past winter, the Arctic sea ice was the lowest since satellite measurements began.

Write to Robert Lee Hotz at sciencejournal@wsj.com