The amount of ice in the Arctic during the depths of winter's freeze hit record lows for the second consecutive year, escalating concerns that sea ice is melting at an alarming rate.
The National Snow and Ice Data Center announced on Monday that Arctic sea ice reached its winter ice cover maximum last Thursday with only 5.6 million square miles frozen. That's down 5,000 square miles from last year's record low, a difference the size of Connecticut. Sea ice has been on a long decline since satellites began monitoring its extent in 1979, with between 173,000 and 196,000 square miles of ice vanishing every decade since then—a loss larger than the state of California.
The below-average sea ice cover is tied to climate change and warmer temperatures afflicting the Arctic all winter. Hotspots near the North Pole and towards the Norwegian archipelago Svalbard climbed to more than 11 degrees above average between December and February.
The winter ice peak occurred later than average, meaning the ice's melting season will be shorter than normal for the upcoming spring and summer, the researchers said.
"I've never seen such a warm, crazy winter in the Arctic," Mark Serreze, director of the Boulder, Colo.-based data center, said in a statement. "The heat was relentless."
Last week, the World Meteorological Organization declared 2015 the hottest year on record by a large margin; this year could be even warmer. The Arctic has warmed twice as fast as the rest of the world over the last few decades.
The North Pole ice cap grows during the winter, usually hitting its peak in March. The sea ice then shrinks until it reaches its smallest point at the end of the summer melting season, usually by mid-September. Last February, Arctic sea ice extent reached its annual maximum level 15 days earlier than the previous 30-year average, peaking at 5.61 million square miles. It was the lowest maximum ever recorded—50,200 square miles below the previous lowest maximum set in 2011, a chunk the size of Louisiana.
The summer minimums in sea ice cover have traditionally captured more interest than the winter maximums, since the most dramatic sea ice loss has typically occurred in September, said Claire Parkinson, climate change senior scientist at NASA. The last time the Arctic summer sea ice shrank to an all-time low was in 2012, when it measured 1.32 million square miles, beating the previous minimum record of 1.61 million square miles set in 2007.
"After 2012 it rebounded a bit, but it's still much lower than it was in the late 1970s," Parkinson said.
The rapid decline of sea ice loss reverberates globally and doesn't just impact the Arctic, said Rafe Pomerance, a member of the Polar Research Board of the National Academy of Sciences and chair of Arctic 21, a coalition of NGO experts on Arctic climate change. The Arctic's white ice-cover reflects heat and light back into space, keeping the entire planet cool. It also shields the ocean from absorbing that heat and prevents the permafrost—the vast, frozen subsurface layer of soil—from melting. As that reflective cover shrinks, however, it causes permafrost to thaw, releasing trapped greenhouse gases into the atmosphere and creating feedbacks that may accelerate how fast the Arctic warms, Pomerance said.
"This is totally outside of anything that has been seen before. It's way outside natural variability," Pomerance said of the vanishing sea ice. "The loss of the Arctic as we know it was predicted—it's just happening a lot sooner."
He added: "I think with regard to the Arctic we need to move from a period of scientific observation to one in which we frame the question, 'What is the Arctic we have to have? What are the services the Arctic provides that we can't afford to lose?'"