A new study reveals that a third of the Arctic’s tundra, forests, and wetlands have shifted from storing carbon to emitting it, as rising temperatures disrupt millennia of carbon storage in the frozen north.

For thousands of years, Arctic land ecosystems acted as a vast carbon reservoir, trapping emissions in permafrost. However, warming temperatures are now turning these ecosystems into carbon sources. Published in Nature Climate Change, the study found that over 30% of the region now emits more CO₂ than it absorbs, increasing to 40% when wildfires are considered.

Researchers analysed data from 200 monitoring sites between 1990 and 2020, showing that Arctic boreal forests, wetlands, and tundra are changing due to rapid warming.

“It is the first time that we’re seeing this shift at such a large scale, cumulatively across all of the tundra. That’s a pretty big deal,” said Sue Natali, a co-author and lead researcher on the study at the Woodwell Climate Research Center.

This transformation is occurring even as the Arctic grows greener.

“One place where I work in interior Alaska, when the permafrost thaws, the plants grow more so you can sometimes can get an uptick in carbon storage,” Natali said. “But the permafrost continues to melt and the microbes take over. You have this really big pool of carbon in the ground and you see things like ground collapse. You can visually see the changes in the landscape,” she said.

The findings add to scientists’ concerns about the natural systems regulating Earth’s climate, which are under increasing strain. Oceans, forests, and soils absorb about half of human emissions, but their capacity to do so is weakening.

Spanning Siberia, Alaska, the Nordic countries, and Canada, the Arctic has been a vital carbon sink for thousands of years, helping cool the planet.

Now, researchers warn that the region’s carbon cycle is shifting and requires closer monitoring to understand and mitigate its impact on global climate change.

Anna Virkkala, the lead author of the study, said: “There is a load of carbon in the Arctic soils. It’s close to half of the Earth’s soil carbon pool. That’s much more than there is in the atmosphere. There’s a huge potential reservoir that should ideally stay in the ground.

“As temperatures get warmer, soils get warmer. In the permafrost, most of the soils have been entirely frozen throughout the full year. But now the temperatures are warmer, there’s more organic matter available for decomposition, and carbon gets released into the atmosphere. This is the permafrost-carbon feedback, which is the key driver here.”