Boreal forest fires released a record-high amount of CO2 in 2021, significantly impacting Earth's climate. Using satellite data, researchers found that these fires emitted 23% of global carbon dioxide from fires, much higher than usual. This increase is due to warmer and drier conditions leading to more extreme fires in boreal forests. The 2021 fires were especially severe because both North American and Eurasian boreal forests experienced significant water deficits. This trend of more intense fires in boreal forests poses a challenge to efforts to mitigate climate change.