The Guardian reports:

The vast expanse of sea ice around Antarctica has suffered a “precipitous” fall since 2014, satellite data shows, and fell at a faster rate than seen in the Arctic.

The plunge in the average annual extent means Antarctica lost as much sea ice in four years as the Arctic lost in 34 years. The cause of the sharp Antarctic losses is as yet unknown and only time will tell whether the ice recovers or continues to decline.

But researchers said it showed ice could disappear much more rapidly than previously thought. Unlike the melting of ice sheets on land, sea ice melting does not raise sea level. But losing bright white sea ice means the sun’s heat is instead absorbed by dark ocean waters, leading to a vicious circle of heating.

Sea ice spreads over enormous areas and has major impacts on the global climate system, with losses in the Arctic strongly linked to extreme weather at lower latitudes, such as heatwaves in Europe.

The loss of sea ice in the Arctic clearly tracks the rise in global air temperatures resulting from human-caused global heating, but the two poles are very different. The Arctic is an ocean surrounded by continents and is exposed to warming air, while Antarctica is a freezing continent surrounded by oceans and is protected from warming air by a circle of strong winds.

Antarctic sea ice had been slowly increasing during the 40 years of measurements and reached a record maximum in 2014. But since then sea ice extent has nosedived, reaching a record low in 2017.

“There has been a huge decrease,” said Claire Parkinson, at Nasa’s Goddard Space Flight Center in the US. In her study, published in the journal Proceedings of the National Academy of Sciences, she called the decline precipitous and a dramatic reversal.

“We don’t know if that decrease is going to continue,” she said. “But it raises the question of why [has it happened], and are we going to see some huge acceleration in the rate of decrease in the Arctic? Only the continued record will let us know.”

“The Arctic has become a poster child for global warming,” Parkinson said, but the recent sea ice falls in Antarctica have been far worse. She has tracked Antarctic sea ice for more than 40 years. “All of us scientists were thinking eventually global warming is going to catch up in the Antarctic,” she said. [Continue reading…]