The long, frigid Arctic autumn and winter began late last week—and the shrinking sea ice has begun to expand anew. That's good news for starving polar bears waiting for the ice to come in so they can hunt. But the dwindling ice pack—courtesy of global warming—bodes ill for Earth's future.

"The continued drastic melting of the Arctic sea ice is a disaster for the polar bear and a harbinger of what's to come for the rest of the world if we don't reduce greenhouse gas emissions," says Kassie Siegel, climate program director at the Center for Biological Diversity, who led the charge to list the polar bear as an endangered species.

This year's ice shrank to just 1.74 million square miles—860,000 square miles less than the average extent since 1979—and only slightly more than last year's record 1.59 million square mile icepack. In fact, the ice retreated so much that for the first time since record-keeping began ships this year could circumnavigate the Arctic Ocean.

Plus, this happened despite cooler temperatures that should have allowed much more ice to survive summer warming. Translation: the climate is shifting fast towards a total loss of sea ice in the Arctic in summer, something that hasn't happened during the extent of human civilization.