Terrestrial ecosystems have taken up about 32% of the total anthropogenic CO₂ emissions in the past six decades¹. Large uncertainties in terrestrial carbon–climate feedbacks, however, make it difficult to predict how the land carbon sink will respond to future climate change². Interannual variations in the atmospheric CO₂ growth rate (CGR) are dominated by land–atmosphere carbon fluxes in the tropics, providing an opportunity to explore land carbon–climate interactions^3,4,5,6. It is thought that variations in CGR are largely controlled by temperature^7,8,9,10 but there is also evidence for a tight coupling between water availability and CGR¹¹. Here, we use a record of global atmospheric CO₂, terrestrial water storage and precipitation data to investigate changes in the interannual relationship between tropical land climate conditions and CGR under a changing climate. We find that the interannual relationship between tropical water availability and CGR became increasingly negative during 1989–2018 compared to 1960–1989. This could be related to spatiotemporal changes in tropical water availability anomalies driven by shifts in El Niño/Southern Oscillation teleconnections, including declining spatial compensatory water effects⁹. We also demonstrate that most state-of-the-art coupled Earth System and Land Surface models do not reproduce the intensifying water–carbon coupling. Our results indicate that tropical water availability is increasingly controlling the interannual variability of the terrestrial carbon cycle and modulating tropical terrestrial carbon–climate feedbacks.

过去六十年，陆地生态系统约占人为CO ₂排放总量的32% ¹ 。然而，陆地碳-气候反馈的巨大不确定性使得很难预测陆地碳汇将如何应对未来的气候变化² 。热带地区大气CO ₂增长率(CGR) 的年际变化主要由陆地-大气碳通量主导，这为探索陆地碳-气候相互作用提供了机会^3,4,5,6 。据认为，CGR 的变化主要受温度^{7、8、9、10}控制，但也有证据表明可用水量与 CGR ¹¹之间存在紧密耦合。在这里，我们利用全球大气CO ₂ 、陆地水储存和降水数据的记录来研究气候变化下热带陆地气候条件与CGR之间关系的变化。我们发现，与 1960-1989 年相比，1989-2018 年热带水资源供应量与 CGR 之间的年际关系变得越来越负。这可能与厄尔尼诺/南方涛动遥相关变化驱动的热带水资源供应异常的时空变化有关，包括空间补偿水效应的下降⁹ 。我们还证明，大多数最先进的耦合地球系统和陆地表面模型都不能重现加剧的水碳耦合。我们的研究结果表明，热带水资源的可用性越来越多地控制陆地碳循环的年际变化并调节热带陆地碳气候反馈。