全球水循环（包括植物蒸发蒸腾在内）的加速，被认为是全球变暖对地球系统所产生影响的一个关键指标。蒸发蒸腾指的是通过蒸发和植物呼吸的综合作用从地球的地表向大气层运动的水。Martin Jung及其同事利用一种由数据驱动的机器学习方法和一套基于过程的模型发现，在1982年和1997年间，蒸发蒸腾随全球变暖稳步增加。但从1998年以来，这种增加趋势平缓了下来，很可能是南半球（尤其是非洲和澳大利亚）土壤水分供应的局限性所造成的一个结果。
至于这是一种自然气候变化的构成部分、还是陆地蒸发蒸腾从长远来讲将会更多受到供应限制的一个气候变化信号，仍然有待观察。
推荐英文摘要：
Nature doi:10.1038/nature09396
Recent decline in the global land evapotranspiration trend due to limited moisture supply
Martin Jung,mjung@bgc-jena.mpg.deMarkus Reichstein,mreichstein@bgc-jena.mpg.dePhilippe Ciais,Sonia I. Seneviratne,Justin Sheffield,Michael L. Goulden,Gordon Bonan,Alessandro Cescatti,Jiquan Chen,Richard de Jeu,A. Johannes Dolman,Werner Eugster,Dieter Gerten,Damiano Gianelle,Nadine Gobron,Jens Heinke,John Kimball,Beverly E. Law,Leonardo Montagnani,Qiaozhen Mu,Brigitte Mueller,Keith Oleson,Dario Papale,Andrew D. Richardson,Olivier Roupsard,Steve Running,Enrico Tomelleri,Nicolas Viovy,Ulrich Weber,Christopher Williams,Eric Wood,S?nke Zaehle" Ke Zhang
More than half of the solar energy absorbed by land surfaces is currently used to evaporate water1. Climate change is expected to intensify the hydrological cycle2 and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land―a key diagnostic criterion of the effects of climate change and variability―remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network3, meteorological and remote-sensing observations, and a machine-learning algorithm4. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1?±?1.0?millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Ni?o event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science.
