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

Abstract

The Arctic-Boreal Zone is rapidly warming, impacting its large soil carbon stocks. Here we use a new compilation of terrestrial ecosystem CO2 fluxes, geospatial datasets and random forest models to show that although the Arctic-Boreal Zone was overall an increasing terrestrial CO2 sink from 2001 to 2020 (mean +/- standard deviation in net ecosystem exchange, -548 +/- 140 Tg C yr(-1); trend, -14 Tg C yr(-1); P < 0.001), more than 30% of the region was a net CO2 source. Tundra regions may have already started to function on average as CO2 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(-1); trend, -9 Tg C yr(-1)), and the permafrost region becomes CO2 neutral (budget, -24 +/- 123 Tg C yr(-1); trend, -3 Tg C yr(-1)), underscoring the importance of fire in this region.