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Earth’s Arctic region is no longer storing carbon, but rather releasing it into the atmosphere. For millennia, the Arctic Boreal Zone (ABZ) played a key role as a carbon sink, storing vast amounts of carbon dioxide (CO₂) in its frozen soils. Unfortunately, that is no longer the case. New research confirms that this important function is rapidly disappearing due to rising temperatures, increased microbial activity and an increase in wildfires. The study, led by the Woodwell Centre for Climate Research, found that a third of the ABZ is now emitting more carbon than it is absorbing, and this figure rises to 40% when emissions from fires are taken into account.
Changing the carbon balance in the Arctic
The Arctic-boreal zone includes tundra, boreal forests and marshes in the northernmost regions of the Earth. Historically, the zone acted as a carbon sink, sequestering more CO₂ through plant photosynthesis than was released through plant and microbial respiration. However, the study shows that this delicate balance is shifting due to climate change and increased fire activity.
“We wanted to get the most up-to-date and complete picture of the carbon cycle in the north, and to do that we needed to take into account the growing carbon footprint of fires in this region,” said lead author Anna Virkkala, a research fellow at the Woodwell Center for Climate Research.
Data supporting the conclusions
The research team analyzed three decades of CO₂ emission data (1990–2020) from 200 monitoring stations. The data was obtained using special instruments that measure the exchange of gases between the land and the atmosphere. These observations were combined with climate, soil and vegetation data to create the “ABC Flux” database, which Virkkala curates. Analysis of these data allowed the creation of detailed maps (with a resolution of 1 km x 1 km) of carbon fluxes in the region.
“The high resolution of this data allows us to see how diverse the Arctic is in the context of the carbon cycle,” added Sue Natalie, leader of the Permafrost Pathways initiative and co-author of the study.
Summer landscaping vs. winter emissions
The study provides valuable insights into the factors that are changing the carbon balance in the ABZ. While a longer growing season and increased vegetation in some regions contribute to carbon sequestration in summer, these gains are offset by increased carbon emissions in winter. Melting permafrost releases stored carbon, and microbial activity during warmer winters accelerates greenhouse gas emissions.
“We see that the longer growing season and increased microbial activity in winter are gradually changing carbon trajectories,” explained Marguerite Moritz, an assistant professor at the University of Texas at El Paso and co-author of the study.
The study also challenges the assumption that “greening” the Arctic will lead to greater carbon storage. Although almost half (49%) of the ABZ shows signs of greening, only 12% of these regions show an annual increase in CO₂ absorption.
Fires are exacerbating carbon losses in the Arctic
Wildfires, which are an increasing threat to the ABZ, significantly increase carbon emissions. Including fires in the analysis increased the share of the ABZ as a carbon source from 34% to 40%. These fires are fueled by vegetation growth and drier conditions, creating a vicious cycle that accelerates carbon loss.
Consequences for the planet
The findings confirm that the Arctic is gradually transforming from a carbon sink to a carbon source.
“This study could be a wake-up call for future changes and offers a map of regions that need better monitoring in the coming decades,” concluded Anna Virkkala.
The researchers say understanding these changes is important for predicting their long-term impact on the global carbon cycle. The maps created in this study can guide future monitoring efforts and inform climate policy. The study shows that the Arctic's role in regulating the Earth's carbon balance is changing rapidly – and these changes could have global consequences.
