The reduced net carbon uptake over Northern Hemisphere land causes the close-to-normal CO₂ growth rate in 2021 La Niña

La Niña climate anomalies have historically been associated with substantial reductions in the atmospheric CO₂ growth rate. However, the 2021 La Niña exhibited a unique near-neutral impact on the CO₂ growth rate. In this study, we investigate the underlying mechanisms by using an ensemble of net CO₂ fluxes constrained by CO₂ observations from the Orbiting Carbon Observatory-2 in conjunction with estimates of gross primary production and fire carbon emissions. Our analysis reveals that the close-to-normal atmospheric CO₂ growth rate in 2021 was the result of the compensation between increased net carbon uptake over the tropics and reduced net carbon uptake over the Northern Hemisphere mid-latitudes. Specifically, we identify that the extreme drought and warm anomalies in Europe and Asia reduced the net carbon uptake and offset 72% of the increased net carbon uptake over the tropics in 2021. This study contributes to our broader understanding of how regional processes can shape the trajectory of atmospheric CO₂ concentration under climate change.