(CNN)The world's most northerly forests could be a "time bomb" of planet-warming pollution as expanding wildfires have released record high levels of planet-heating pollution into the atmosphere, according to a new study.
Using new satellite data analysis techniques, researchers found that, since 2000, summer wildfires have expanded in boreal forests, which wrap around the northernmost parts of the Earth.
Boreal forest fires usually make up 10% of global wildfire-related carbon pollution. But in 2021, their contribution soared to 23%, according to the study, as extreme drought and heatwaves in Siberia and Canada helped drive intense fires.
"Boreal forests could be a time bomb of carbon, and the recent increases in wildfire emissions we see make me worry the clock is ticking," said study author Steven Davis, a professor of earth system science at the University of California at Irvine, in a press release.
A member of Russia's Aerial Forest Protection Service pictured during wildfires in July 2021.
These forests, which cover huge swaths of Canada, Russia and Alaska, are the world's largest land biome. They are also carbon dense, releasing 10 to 20 times more planet-heating carbon pollution for each unit of area burned by wildfires than other ecosystems, according to the study.
Boreal forests are one of the fastest warming biomes on Earth, and warmer and drier fire seasons are contributing to expanding wildfires.
Russia's Siberian region experienced particularly bad wildfires in 2021 which burned nearly 45 million acres (18.16 million hectares) of Russian forest in 2021.
In July that year, reconnaissance pilot Svyatoslav Kolesov told CNN he couldn't fly his plane in the far eastern Russian region of Yukutia because smoke from the fires was so thick.
The region is prone to wildf