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12:17:47 
2025-02-01 
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Large swathes of one of Earth's largest carbon sinks are now emitting rather than capturing CO2.
More than a third of the Arctic-Boreal Zone (ABZ) – including the tundra, forests, and wetlands around the Arctic Circle – is pushing out carbon rather than sucking it up, according to new research from an international team, led by scientists at the Woodwell Climate Research Center in Massachusetts.
The same reversal is happening in parts of the Amazon Rainforest, too.
While the ABZ as a whole is still considered a carbon sink – as it has been for millennia – rising global temperatures are putting some key regions at risk, and detailed monitoring is needed to understand how those places are faring.
"While we found many northern ecosystems are still acting as carbon dioxide sinks, source regions and fires are now canceling out much of that net uptake and reversing long-standing trends," says ecologist Anna Virkkala, from Woodwell Climate.
That fire element is crucial: the researchers found that wildfires are becoming more frequent and impactful in the ABZ. The stats show that when wildfires are considered, 40 percent of the ABZ gave off more CO2 than it absorbed between 2001 and 2020, compared to just 34 percent when wildfires weren't included.
Those numbers are based on high-resolution data, carefully compiled from 200 carbon monitoring stations, known as the ABC Flux network, plus additional field measurements, meteorological information, and computer modeling.
The results change across the seasons. During summer, the ABZ's carbon sink is most influential, with greener vegetation and more photosynthesis taking place. In winter, however, unusually warm temperatures are increasing the amount of soil and organic matter exposed to the air, which means a greater release of CO2 than is typical.
"That variability isn't surprising because the Arctic isn't one single place – it's a massive area with diverse ecosystems and climatic conditions," says ecologist Sue Natali, from Woodwell Climate.
"And now we have the capability to track and map carbon processes at a spatial resolution that can reveal what's happening on the ground."
Across the study period of 1990 to 2020, the researchers found the ABZ became more of a carbon sink, not less, on average. That seems like good news, but hotspots of variability – particularly in tundra regions – are trending the other way (as previous research has shown).
Nearly half of the carbon stored in soil on the planet is thought to be in this region.
To plot how our planet is changing, we need to know how these parts of the ABZ are breathing in and out across the year – and how a warmer, greener Arctic might contribute to global atmospheric changes.
"Highly collaborative efforts like this are critical for understanding how shifting seasonal dynamics and disturbance patterns can have regional and even global impacts," says ecologist Marguerite Mauritz, from the University of Texas-El Paso.
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