North Pole surging above freezing in the dead of winter

The sun won’t rise at the North Pole until March 20, and it’s normally close to the coldest time of year, but an extraordinary and possibly historic thaw swelled over the tip of the planet last weekend. Analyses show that the temperature warmed to the melting point as an enormous storm pumped an intense pulse of heat through the Greenland Sea.

Temperaturesmay have soared as high as 35 degrees (2 degrees Celsius) at the pole, according to the U. S. Global Forecast System model. While there are no direct measurements of temperature there, Zack Labe, a climate scientist working on his doctorate at the University of California at Irvine, confirmed that several independent analyses showed “it was very close to freezing,” which is more than 50 degrees (30 degrees Celsius) above normal.

The warm intrusion penetrated right through the heart of the Central Arctic, Mr. Labe said. The temperature averaged for the entire region north of 80 degrees latitude spiked to its highest level ever recorded in February. The average temperature was more than 36 degrees (20 degrees Celsius) above normal. “No other warm intrusions were very close to this,” Mr. Labe said in an interview, describing a data set maintained by the Danish Meteorological Institute that dates back to 1958. “I was taken by surprise how expansive this warm intrusion was.”

Such extreme warm intrusions in the Arctic, once rare, are becoming more routine, research has shown. A study published in July found that since 1980, these events are becoming more frequent, longer-lasting and moreintense.

“Previously this was not common,” said lead author of the study Robert Graham, from the Norwegian Polar Institute, in an email. “It happened in four years between 19802010, but has now occurred in four out of the last five winters.”

Mr. Graham explained that these warming events are related to the decline of winter sea ice in the Arctic, noting that January’s ice extent was the lowest on record. “As the sea ice is melting and thinning, it is becoming more vulnerable to these winter storms,” he explained.

“The thinner ice drifts more quickly and can break up into smaller pieces. The strong winds from the south can push the ice further north into the Central Arctic, exposing the open water and releasing heat to the atmosphere from the ocean.”

Scientists were shocked in recent days to discover open water north of Greenland, an area normally covered by old, very thick ice.

Such warm water is appearing to have an effect on air temperatures. At the north tip of Greenland, about 400 miles to the south of the North Pole, the weather station Cape Morris Jesup has logged a record-crushing 61 hours above freezing so far this calendar year. The previous record, dating to 1980, was 16 hours through the end of April in 2011.