Vincent Humphrey, Jakob Zscheischler, Philippe Ciais; et al.

　　Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO2) emissions, thereby slowing the increase of CO2 concentration in the atmosphere1. Year-to-year variations in the atmospheric CO2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems1. The sensitivity of these fluctuations to changes in tropical temperature has been well documented 2,3,4,5,6, but identifying the role of global water availability has proved to be elusive. So far, the only usable proxies for water availability have been time-lagged precipitation anomalies and drought indices 3,4,5, owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO2 growth. We demonstrate that this global relationship is independent of known temperature effects and is underestimated in current carbon cycle models. Our results indicate that interannual fluctuations in terrestrial water storage strongly affect the terrestrial carbon sink and highlight the importance of the interactions between the water and carbon cycles.

　　（来源：Nature, 2018, DOI: 10.1038/s41586-018-0424-4）

  陆地生态系统平均可吸收30%的人为二氧化碳排放，从而减缓了大气中二氧化碳浓度的增加。大气中二氧化碳增长率的年际变化主要是由于陆地生态系统吸收的碳存在波动。已有记录显示这些波动对热带气温变化的敏感性，但是测量全球可利用水的作用相当困难。由于缺乏直接的观察，目前一直使用时间滞后的降水异常和干旱指数等指标来代表生态系统中的可利用水量。虽然这些指标使用方便，但只考虑了水的输入，忽略了由于蒸发和径流造成的水损失。研究发现，大气中二氧化碳的增长率对观测到的陆地水储量变化非常敏感，更干旱的年份与更快的大气二氧化碳增长有关。在干旱的2015年，自然生态系统从大气中吸收的碳比正常年份少30%左右，而大气中的二氧化碳浓度比正常年份增加更快。相反，在有记录以来最潮湿的2011年，大气中二氧化碳浓度的增加速度要慢得多。研究证明：干旱的影响比之前通过植被模型估计的更严重。研究结果表明，陆地水储量的年际波动强烈地影响陆地碳汇，强调了水与碳循环相互作用的重要性。