NASA Goddard Institute for Space Studies, New York, NY, USA.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA.
Nature. 2019 May;569(7754):59-65. doi: 10.1038/s41586-019-1149-8. Epub 2019 May 1.
Although anthropogenic climate change is expected to have caused large shifts in temperature and rainfall, the detection of human influence on global drought has been complicated by large internal variability and the brevity of observational records. Here we address these challenges using reconstructions of the Palmer drought severity index obtained with data from tree rings that span the past millennium. We show that three distinct periods are identifiable in climate models, observations and reconstructions during the twentieth century. In recent decades (1981 to present), the signal of greenhouse gas forcing is present but not yet detectable at high confidence. Observations and reconstructions differ significantly from an expected pattern of greenhouse gas forcing around mid-century (1950-1975), coinciding with a global increase in aerosol forcing. In the first half of the century (1900-1949), however, a signal of greenhouse-gas-forced change is robustly detectable. Multiple observational datasets and reconstructions using data from tree rings confirm that human activities were probably affecting the worldwide risk of droughts as early as the beginning of the twentieth century.
尽管人为气候变化预计会导致温度和降雨量的大幅变化，但由于内部变异性大且观测记录时间短，全球干旱的人为影响的检测变得复杂。在这里，我们使用跨越过去千年的树木年轮数据获得的帕尔默干旱严重指数重建来解决这些挑战。我们表明，在二十世纪，气候模型、观测和重建中可以识别出三个不同的时期。在最近几十年（1981 年至今），温室气体强迫的信号已经存在，但还不能确定。观测和重建与预期的中期（1950-1975 年）温室气体强迫模式差异显著，这与气溶胶强迫的全球增加相吻合。然而，在本世纪的前半叶（1900-1949 年），温室气体强迫变化的信号是可靠的。多个观测数据集和使用树木年轮数据的重建证实，早在二十世纪初，人类活动可能就已经在影响全球干旱的风险。
