Earth's Arctic region has flipped and now emits more carbon than it stores

For millennia, the Arctic-boreal zone (ABZ) has acted as a critical carbon reservoir, locking away vast amounts of carbon dioxide (CO₂) in its frozen soils. Unfortunately, this seems to no longer be true.

A new study confirms that this vital role is rapidly eroding due to rising temperatures, increased microbial activity, and intensifying wildfires. 

The research, led by the Woodwell Climate Research Center, shows that one-third of the ABZ is now emitting more carbon than it absorbs, with this figure rising to 40% when emissions from fires are factored in.

Shifting carbon balance in the Arctic

The Arctic-boreal zone encompasses tundra, boreal forests, and wetlands across Earth’s northernmost regions. 

Historically, the ABZ has acted as a net carbon sink, absorbing more CO₂ through plant photosynthesis than it released via microbial and plant respiration.

However, the study highlights how this delicate balance is shifting, driven by climate change and a surge in wildfires.

“We wanted to develop the most current and comprehensive picture of carbon in the north, and to do that, we knew we needed to account for fire’s growing carbon footprint in this region,” said lead author Anna Virkkala, a research scientist at Woodwell Climate. 

“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.”

Data behind the findings

To assess the ABZ’s changing carbon dynamics, the research team compiled three decades of CO₂ data (1990–2020) from 200 monitoring sites.

The data were drawn from flux towers and chambers that measure gas exchanges between the land and the atmosphere. 

These site-level observations were integrated with climate, soil, and vegetation data into the “ABC Flux” database, which Virkkala oversees.

The process of “upscaling” these data created detailed, high-resolution maps (1km x 1km) of carbon fluxes across the region. This level of detail allowed researchers to pinpoint specific areas where carbon trends are shifting.

“The high resolution of these data means that we can now see how variable the Arctic is when it comes to carbon,” said Sue Natali, lead of the Permafrost Pathways initiative at Woodwell Climate and a co-author of the study. 

“The Arctic isn’t one single place – it’s a massive area with diverse ecosystems and climatic conditions. 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.”

Summer greening vs. winter emissions

The study provides key insights into the factors driving the ABZ’s changing carbon balance.

While longer growing seasons and increased vegetation in some areas have boosted summer carbon uptake, these gains are overshadowed by increased emissions during the non-growing season. 

Thawing permafrost releases stored carbon, and microbial activity during warmer winters accelerates the release of greenhouse gases.

“We are seeing that longer growing seasons and more microbial activity in winter are gradually shifting carbon trajectories,” explained Marguerite Mauritz, an assistant professor at the University of Texas-El Paso and co-author of the study.

The research also challenges the assumption that a “greener” Arctic will lead to greater carbon storage. While nearly half (49%) of the ABZ showed signs of greening, only 12% of those areas demonstrated an annual net increase in CO₂ uptake. 

Warmer conditions often mean more carbon released from permafrost thaw and more biomass available to burn during wildfires, further contributing to emissions.

Fires amplify Arctic carbon loss

Wildfires, a growing threat in the ABZ, exacerbate the region’s carbon release. Adding fire emissions to the carbon balance analysis raised the percentage of the ABZ acting as a carbon source from 34% to 40%. 

These fires are fueled by increased vegetation and drier conditions, creating a feedback loop that accelerates carbon loss.

The study highlights the need for more robust monitoring of the ABZ to better understand and mitigate the impacts of these changes.

“Highly collaborative efforts like this are critical for understanding how shifting seasonal dynamics and disturbance patterns can have regional and even global impacts,” Mauritz said.

Implications for the planet

The findings are consistent with a growing body of research indicating that the Arctic is transitioning from a carbon sink to a carbon source.

Studies including methane (CH₄) emissions from lakes, rivers, and wetlands reinforce this troubling trend. 

A warmer Arctic may no longer serve as a reliable buffer against global carbon emissions but instead act as a significant contributor.

“This study may act as a warning sign of bigger changes ahead, and offers a map of places we’ll need to better monitor in the coming decades,” Virkkala said.

Arctic warming and carbon dynamics

The researchers emphasize that understanding these changes is essential for predicting their long-term impact on the global carbon cycle.

The detailed, high-resolution maps created by this study can guide future monitoring efforts and inform climate policy.

By illustrating how and where carbon dynamics are shifting, this research provides critical tools for scientists and policymakers to address the challenges posed by a warming Arctic. 

As the study shows, the region’s role in regulating Earth’s carbon balance is changing rapidly – and the consequences may reverberate far beyond the northern latitudes.

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