With previous reports that the Arctic this winter has been unsettlingly warm, with some regions experiencing temperatures 20°C (36°F) hotter than they should be at this time of the year, it is perhaps unsurprising that the ice extent for the Arctic this November was the lowest on record.

But now it seems that it’s not only the Northern Hemisphere that is experiencing an unusually balmy period, as Antarctic sea ice is similarly struggling to form. “Antarctic sea ice really went down the rabbit hole this time,” says Ted Scambos, lead scientist at the National Snow and Ice Data Center, in a statement. “There are a few things we can say about what happened, but we need to look deeper.”

Even though Antarctic sea ice extent has typically increased over the last few decades due mainly to shifting currents and wind patterns, November this year truly bucked the trend. The ice surrounding the continent declined sharply last month, with the average extent 1.81 million square kilometers (699,000 square miles) lower than the 1981 to 2010 average. That’s an area of sea ice roughly the same size as Libya.

^{National Snow and Ice Data Center}

While it is technically summer in the Southern Hemisphere, the air temperatures over some parts of the Antarctic continent have been 2-4°C (4-7°F) warmer than average for this time of the year. Coupled with an earlier pattern of strong westerly winds, the sea ice pack surrounding the continent has become even more dispersed. There have also been large areas of water within the sea ice opening up, which has reduced the overall extent of the ice.

^{National Snow and Ice Data Center}

“The Arctic has typically been where the most interest lies, but this month, the Antarctic has flipped the script and it is southern sea ice that is surprising us,” says NASA scientist Walt Meier. But that doesn’t mean you shouldn’t be worried about the Arctic, as the records from this month show that while the sea ice extent should be growing as it enters winter, there was a period last month when it actually decreased, something that is deeply disturbing.

With both the Northern and Southern Hemisphere warming at unprecedented levels, no one really knows what to expect. Hopefully, the ice in the North will start expanding again throughout the winter months, but the long-term impacts on the Arctic and Antarctic are basically unknown.