Carbon Source/Sink Balance from the Arctic-Boreal Zone: Sources Continue to Increase Relative to Sinks: Carbon Cycle Changes in the Arctic Permafrost Region Led by Accelerated Arctic Warming

     In the past, a higher percentage of the Arctic-Boreal Zones (ABZ) were net carbon sinks than today. One reason is the increasing wildfires in these regions. The capacity for carbon storage in the ABZ is less than it was. According to Phys.org:

“An international team led by Woodwell Climate Research Center found that a third (34%) of the Arctic-boreal zone (ABZ)—the treeless tundra, boreal forests, and wetlands that make up Earth's northern latitudes—is now a source of carbon to the atmosphere. That balance sheet is made up of carbon dioxide (CO2) uptake from plant photosynthesis and CO2 released to the atmosphere through microbial and plant respiration.”

“When emissions from fire were added, the percentage grew to 40%.”

     The recent research on carbon budgeting in the ABZ is the most comprehensive to date. According to Dr. Anna Virkkala, a research scientist at the Permafrost Pathways initiative at Woodwell Climate and lead author of the study:

"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 is collected at carbon flux monitoring towers and chambers, which track gas exchange between the land and the atmosphere. This data is integrated with climate, soil, and vegetation data to derive the maps of inhalations and exhalations of gases, including CO2. The study found that carbon uptake in the summers has increased over the 30 years of data recording, but more carbon emissions are being released from the tundra during the non-growing season months. The high-resolution geospatial data shows the significant variability of different sections of the ABZ in terms of carbon sink/source balance. The variability is expected due to the diversity of ecosystems and climatic conditions across the ABZ. Longer growing seasons and increased winter microbial activity are driving the changes.

     Phys.org notes that while this study focuses on terrestrial CO2 fluxes, other studies of lakes, rivers, and wetlands in the ABZ show that natural methane emissions are increasing.

“But the recent cache of upscaling results tells similar stories: namely, that trendlines in the northern latitudes are beginning to turn, and a warmer, greener Arctic does not reliably translate to more carbon storage there—in part because warmer has meant emissions from permafrost thaw and greener, more carbon to combust.”

“For example, the study found that while 49% of the ABZ region experienced "greening"—in which longer growing seasons and more vegetation means that more carbon can be photosynthesized and stored—only 12% of those greening pixels on the map showed an annual increasing net uptake of CO2.”

The abstract of the paper is shown below followed by an explanation of the improvement in data quality and integration across the whole ABZ.

 

“Here we address this knowledge gap using an ABZ CO2 flux dataset that includes monthly terrestrial photosynthesis (gross primary productivity (GPP)), ecosystem respiration (Reco) and NEE data from 200 terrestrial eddy covariance and flux chamber sites (4,897 site-months). This dataset is at least four times larger than ones used in earlier upscaling efforts and covers a longer period, with data extending to 2020. The same dataset was previously used to analyse in situ CO2 flux trends in permafrost versus non-permafrost regions, with the conclusion that the annual net uptake is increasing in the non-permafrost region but not in the permafrost region20. Here we extend that study from the site level to the full ABZ region by combining flux observations with meteorological, remote sensing and soil data, together with random forest models, to estimate CO2 budgets across the ABZ. We do this upscaling over two periods, 2001–2020 (1-km resolution) and 1990–2016 (8-km resolution); the results in the main text are based on the 1-km models unless stated otherwise. We then assess regional and seasonal patterns and trends in ABZ ecosystem CO2 fluxes and their environmental drivers. We also integrate annual fire emissions from 2002 to 202021 to provide near-complete terrestrial CO2 budget estimates (referred to as NEE + fire).”

More figures from the paper are shown below.

 

     In my last three posts, I have shown that new research on carbon cycle analysis and sulfur cycle analysis is changing future warming predictions. This new knowledge should be incorporated into regional and global climate modeling to further refine our understanding.

 

 

References:

 

After millennia as CO₂ sink, more than one-third of Arctic-boreal region is now a source. Science X staff. Phys.org. January 21, 2025. After millennia as CO₂ sink, more than one-third of Arctic-boreal region is now a source

Wildfires offset the increasing but spatially heterogeneous Arctic–boreal CO2 uptake. Anna-Maria Virkkala, Brendan M. Rogers, Jennifer D. Watts, Kyle A. Arndt, Stefano Potter, Isabel Wargowsky, Edward A. G. Schuur, Craig R. See, Marguerite Mauritz, Julia Boike, M. Syndonia Bret-Harte, Eleanor J. Burke, Arden Burrell, Namyi Chae, Abhishek Chatterjee, Frederic Chevallier, Torben R. Christensen, Roisin Commane, Han Dolman, Colin W. Edgar, Bo Elberling, Craig A. Emmerton, Eugenie S. Euskirchen, Liang Feng, …Susan M. Natali. Nature Climate Change (2025). Wildfires offset the increasing but spatially heterogeneous Arctic–boreal CO2 uptake | Nature Climate Change