Even in Earth’s high northern-latitude forest, climate change is predicted to make wildfires more frequent and severe. Earth’s far north hosts the boreal forest, a vast green belt that stretches from North America to Siberia. The boreal forest is one of the world’s largest CO₂ sinks. Over the past few thousand years it has removed around 1 trillion tonnes of carbon from the air, storing it in the trees and soil. Because of the large amount of carbon stored in the boreal forest, fires here can release much more CO₂ into the air than forest fires elsewhere, amplifying climate change. Wildfires release lots of climate-warming CO₂ while they rage. But our research in the European part of this forest has shown that the forest’s CO₂ sink recovers slowly, with the burnt area continuing to release CO₂ for several years after the fires die. This exceeds the amount of CO₂ produced from the fire itself.