In the far North, fire season usually doesn’t start until June, when snow has melted away and summer lightning storms sweep into the region. So scientist Sander Veraverbeke was confused when in May of 2016 he saw little flecks of fire on some satellite images from Alaska and the Northwest Territories.

“I was like, what the hell is going on?” says Veraverbeke, an Earth scientist at the Vrije Universiteit of Amsterdam in the Netherlands.

What he saw on the satellite images were “zombie fires,” remnants of burns from the previous year that somehow stayed alive, smoldering underground, through the long, cold winter.

Zombie fires aren’t an entirely new phenomenon in the Arctic; fire managers have noted occasional flare-ups in past decades. But Veraverbeke’s