Alaskan forests used to be important players in Mother Nature’s game plan for regulating carbon dioxide levels in the air. It’s elementary earth science: Trees take up carbon dioxide and give off oxygen. But now, American and Canadian researchers report that climate change is causing wildfires to burn larger swaths of Alaskan trees and to char the groundcover more severely, turning the black spruce forests of Alaska from repositories of carbon to generators of it. And the more carbon dioxide they release, the greater impact that may have in turn on future climate change.