The study, conducted by an international team led by the Woodwell Climate Research Center, found that 34 percent of the Arctic-boreal zone (ABZ) - encompassing tundra, boreal forests, and wetlands - now emits more carbon dioxide (CO2) than it absorbs. When fire-related emissions were factored in, this figure increased to 40 percent.
The researchers provided the most detailed assessment of carbon fluxes in the ABZ to date, drawing on data from 200 sites between 1990 and 2020. This analysis included year-round dynamics and recent climate changes, capturing the shifting patterns of carbon storage and release in the region.
"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," explained Dr. Anna Virkkala, lead author of the study and research scientist at Woodwell Climate's Permafrost Pathways initiative. "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."
This study measured the land's "breathing" - the gases it emits and absorbs - using carbon flux monitoring towers and chambers. The gathered data were analyzed in a comprehensive repository known as "ABC Flux," which Dr. Virkkala manages. By synthesizing site-level measurements with climate, soil, and vegetation records, researchers created detailed maps illustrating the region's carbon activity.
Over the past 30 years, summer carbon uptake has risen, but this has been outweighed by emissions during non-growing seasons. High-resolution data (1km x 1km from 2001-2020) revealed variability within the Arctic's ecosystems and the regions most affected by these changes.
"The high resolution of these data means that we can now see how variable the Arctic is when it comes to carbon," said Dr. Sue Natali, co-author and lead of Permafrost Pathways at Woodwell Climate. "That variability isn't surprising because 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."
"We are seeing that longer growing seasons and more microbial activity in winter are gradually shifting carbon trajectories," added Dr. Marguerite Mauritz, assistant professor at the University of Texas-El Paso and a study co-author. "Highly collaborative efforts like this are critical for understanding how shifting seasonal dynamics and disturbance patterns can have regional and even global impacts."
The study builds on a growing body of research showing that the Arctic's historical role as a carbon sink is changing. While this study focused on CO2 fluxes on land, recent findings incorporating methane (CH4) emissions from lakes, rivers, and wetlands indicate that the permafrost region is becoming a carbon source.
The new data also challenge assumptions about a greener Arctic translating to greater carbon storage. While 49 percent of the ABZ experienced "greening"-with longer growing seasons and increased vegetation-only 12 percent of these areas showed a net annual increase in CO2 uptake.
"Carbon cycling in the permafrost region is really starting to change," said Virkkala. "Our 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."
Research Report:Wildfires offset the increasing but spatially heterogeneous Arctic-boreal CO2 uptake
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