Atmospheric O 2 reveals a strengthening ocean carbon sink and a stagnant net land sink since 1990

The global ocean and land biosphere absorb roughly half of fossil fuel carbon dioxide (CO 2 ) emissions. The temporal evolution of these sinks remains difficult to quantify owing to data sparsity. Leveraging 30+ years of atmospheric oxygen (O 2 ) and CO 2 observations, we find that the ocean carbon sink increased by 0.63 ± 0.19 petagrams of carbon per year per decade (Pg C year −1 decade −1 ) (a mean of 2.8 ± 0.4 Pg C year −1 ), accounting for 35% of fossil emissions between 1990 and 2019. The net land sink shows no robust trend (with a mean of 1.0 ± 0.5 Pg C year −1 , accounting for 13% of fossil emissions), despite large decadal variability. These results challenge many process-based model simulations of the land and ocean sinks, questioning their ability to accurately predict future climate states.