Over recent decades, terrestrial ecosystems have evolved as potent combatants in our fight against climate change, reflecting a global trend of increased carbon uptake. This enhanced terrestrial carbon sink, absorbing a considerable fraction of anthropogenic carbon emissions, serves as a crucial buffer, substantially mitigating the pace of global warming. Current theory posits that a CO₂-induced increase in global photosynthesis, known as the CO₂ fertilization effect, contributes significantly to the prevailing terrestrial carbon sink. However, this CO₂ fertilization effect, expected to decrease as a function of CO₂, may likely be counterbalanced by the adverse impacts of global warming-induced changes in disturbance regimes, such as drought, fire, and pests. The responses to these present-day forcings remain poorly understood, as do the associated future outcomes.

Here, I synthesize results from several studies on the global land carbon sink, focusing particularly on the roles of CO₂-induced enhancements in light and water-use efficiency, alongside drought-induced risks. Employing a combination of observational data, experimental outcomes, machine learning and modeling techniques, we provide a comprehensive evaluation of these dynamics. Our results suggest that the expanded carbon sink has substantially decelerated climate change; however, projections predict a potential halt in this trend in the latter half of this century. This impending halt could possibly amplify future climate scenarios, emphasizing the urgency of identifying additional mitigation strategies.

We identify droughts, especially their extent and interaction with CO₂-induced enhancements in water-use efficiency, as considerable sources of uncertainty for future land carbon uptake. Additionally, our results suggest groundwater access as a critical, yet largely overlooked factor in current projections, necessitating further exploration and model refinement. Furthermore, we propose that land management, if aimed towards maximizing carbon uptake, harbors significant potential to fortify the land sink. Factoring in accurate climate change impacts into land management decisions could potentially help counter the anticipated reductions in land carbon uptake.