Arctic sea ice, which already hit a record low for winter extent this year, is also younger and thinner now than at almost any time since the satellite record was begun in the late 1970s, scientists said Wednesday.
As of mid-March, 70 percent of the ice was formed within the past year and only 30 percent was multiyear ice, the National Snow and Ice Data Center said in a report that summarized conditions over the past winter. That is a reversal of the proportions that existed in the mid-1980s, when most ice was at least 2 years old.
The oldest ice -- ice that has remained intact for at least five years -- is at a record low for the satellite era and accounts for only 3 percent of the total ice, the Colorado-based center said in its report.
Since first-year ice is usually only 5 to 6.5 feet thick, its predominance is a sign of a thinner ice pack.
The oldest ice is now generally melting out after three or four years or being pushed out of the Fram Strait between Greenland and Svalbard, the center's scientists said.
"The bottom line is that ice no longer survives in the Arctic for very long," they wrote in the report. "This is a big change from the past, when much of the ice cover would survive upwards of a decade."
The current conditions follow a "highly unusual winter in the Arctic, characterized by persistent warmth in the atmosphere that helped to limit ice growth," the report said.
One unusual weather event happened in late December, when warm air shot up from the tropical Atlantic to the Arctic and briefly took temperatures near the North Pole almost to the point of thaw, causing some midwinter ice thinning.
During that period, ice in the Kara and Barents seas thinned by about a foot, the center said. Similar midwinter thinning also happened north of Greenland and off Siberia, the center said.
Ice extent -- the area where ice covers at least 15 percent of the sea surface -- has been running low all winter, and last month was no exception.
Sea-ice extent typically reaches its peak in early or mid-March, then melts to its nadir in September. This year's peak extent, the lowest on the satellite record, was relatively late, on March 24. Since then, extent has declined fairly sharply. Last year's peak extent -- now the second-lowest in the satellite record -- came early, on Feb. 25, 2015, and launched an early start to the melt season.
Ice extent isn't the only statistic to recently be recorded at especially low levels.
Northern Hemisphere snow cover in March was the second-lowest in a 50-year record kept by the Rutgers University Global Snow Lab, the National Snow and Ice Data Center said.
There is a correlation between low snow cover and low September sea ice, said Julienne Stroeve, a senior research scientist at the center.
"It could be that the low snow cover influences the atmosphere in such a way that we end up with reduced sea ice," she said in an email.