Wildfires offset the increasing but spatially heterogeneous Arctic–boreal CO2 uptake

<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">The Arctic–Boreal Zone is rapidly warming, impacting its large soil carbon stocks. Here we use a new compilation of terrestrial ecosystem CO</span>₂<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> fluxes, geospatial datasets and random forest models to show that although the Arctic–Boreal Zone was overall an increasing terrestrial CO</span>₂<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> sink from 2001 to 2020 (mean ± standard deviation in net ecosystem exchange, −548 ± 140 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">; trend, −14 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">; </span><i>P</i><span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> &lt; 0.001), more than 30% of the region was a net CO</span>₂<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> source. Tundra regions may have already started to function on average as CO</span>₂<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> sources, demonstrating a shift in carbon dynamics. When fire emissions are factored in, the increasing Arctic–Boreal Zone sink is no longer statistically significant (budget, −319 ± 140 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">; trend, −9 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">), and the permafrost region becomes CO</span>₂<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);"> neutral (budget, −24 ± 123 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">; trend, −3 Tg C yr</span>⁻¹<span style="background-color:rgb(255,255,255);color:rgb(34,34,34);">), underscoring the importance of fire in this region.</span>