November started out pretty normal for the Arctic. The sun had set for the season, temperatures were dropping, ice was growing rapidly. Winter was coming, right on schedule. And then, a few days ago, everything came screeching to a halt. Ice stopped forming. And then it actually started to melt, thanks to a sudden heat wave that blistered the region with temperatures 20 to 30 degrees Fahrenheit above average. For now, the mass of warm air doesn’t appear to be going anywhere.

That’s bad news for sea ice. Coverage in the Arctic was already at its lowest levels since researchers began using satellite data to measure it back in 1978. And as of November 19, Arctic sea ice was nearly 350,000 square miles below its extent in 2012, the last record-low year. The extreme weather has scientists scrambling to figure out what’s causing the historical temperatures, and more importantly, what their long-term impacts could be.