Large live biomass carbon losses from droughts in the northern temperate ecosystems during 2016-2022.

Abstract

Northern ecosystems (≥ 30° N) have been accumulating vegetation biomass carbon in recent decades, but increasing droughts and wildfires threaten this carbon sink. Here, we analyse annual changes in live vegetation biomass in northern ecosystems using low-frequency microwave satellite observations at 25 km spatial resolution from 2010 to 2022. We find that live biomass carbon stocks have undergone a reversal from a positive to a negative trend during the study period with 2016 marking the turning point. During 2016-2022, live biomass carbon stocks decreased at a rate of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mo>-</mo> <mi>0.20</mi></mrow> <mrow><mo>-</mo> <mi>0.26</mi></mrow> <mrow><mo>-</mo> <mi>0.11</mi></mrow> </msubsup> </math> PgC yr^-1 across northern ecosystems, primarily in temperate biomes ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mo>-</mo> <mi>0.26</mi></mrow> <mrow><mo>-</mo> <mi>0.33</mi></mrow> <mrow><mo>-</mo> <mi>0.17</mi></mrow> </msubsup> </math> PgC yr^-1). The annual mean gross loss of 4% of live biomass carbon in this region during 2016-2022 reflects high interannual variability, with significant losses associated with droughts and a further drop of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mo>-</mo> <mi>0.60</mi></mrow> <mrow><mo>-</mo> <mi>0.75</mi></mrow> <mrow><mo>-</mo> <mi>0.47</mi></mrow> </msubsup> </math> PgC in the very dry year of 2022. Our findings highlight the vulnerability of live biomass carbon stocks to emerging climate-induced disturbances in northern ecosystems, challenging the sustainability of the current large terrestrial carbon sink in this key region for the global carbon balance.