Antarctica’s sea ice hits a record low

At its largest expanse this year, sea ice covered less than 6.6 million square miles of the Antarctic — an area that is almost 400,000 square miles smaller than the previous record low set in 1986, according to preliminary figures released Monday by the National Snow and Ice Data Center at the University of Colorado, Boulder. The number represents the smallest peak extent in almost 45 years of satellite records.

Peak Antarctic ice coverage during the region’s winter, which is the northern hemisphere’s summer, likely occurred on Sept. 10. On that date sea ice stretched over 16.96 million square kilometers, after which it began to shrink, the NSIDC said. This took place almost two weeks earlier than the median date of Sept. 23 between 1981 and 2010.

“There is some concern that this may be the beginning of a long-term trend of decline for Antarctic sea ice, since oceans are warming globally, and warm water mixing in the Southern Ocean polar layer could continue,” the NSIDC said in a news release.

While the drivers of the loss are complicated, and not fully understood, scientists believe climate change plays a role, and continuing shrinking of the ice could exacerbate warming’s effects, as less ice means less sunlight is reflected back into space. Scientists who study Antarctica observed months ago that the ice was struggling to grow back from its February nadir, in a stark deviation from usual patterns.

“The last three or four months now is nothing like we’ve seen before, or would have expected, ever,” said Cecilia Bitz, a climate scientist specializing in sea ice at the University of Washington. “This tells me that the climate change we’re seeing is outside our range of experience and can’t be explained by natural variability.”

If sea-ice coverage that is dramatically lower than usual continues, more of the coastline will be exposed to ocean waves, the effects of which are not yet clear, the NSIDC noted. Scientists have ideas about how sea ice and oceans interact in the Antarctic but most are theoretical and more study is needed, Bitz said.

In the Antarctic, sea ice typically covers the largest expanse of ocean at some point in September. After that, it begins a slow melt over the southern hemisphere’s summer, with the most open water typically seen in early March. The process is the same in the Arctic, though the winter-summer months are reversed.