Despite the pervasive impact of drought on human and natural systems, the large-scale mechanisms conducive to regional drying remain poorly understood. Here we use a multivariate approach^1,2 to identify two distinct externally forced fingerprints from multiple ensembles of Earth system model simulations. The leading fingerprint, F_M1(x), is characterized by global warming, intensified wet–dry patterns³ and progressive large-scale continental aridification, largely driven by multidecadal increases in greenhouse gas (GHG) emissions. The second fingerprint, F_M2(x), captures a pronounced interhemispheric temperature contrast^4,5, associated meridional shifts in the intertropical convergence zone^6,7,8,9 and correlated anomalies in precipitation and aridity over California¹⁰, the Sahel^11,12 and India. F_M2(x) exhibits nonlinear temporal behaviour: the intertropical convergence zone moves southwards before 1975 in response to increases in hemispherically asymmetric sulfate aerosol emissions, and it shifts northwards after 1975 due to reduced sulfur dioxide emissions and the GHG-induced warming of Northern Hemisphere landmasses. Both fingerprints are statistically identifiable in observations of joint changes in temperature, rainfall and aridity during 1950–2014. We show that the reliable simulation of these changes requires combined forcing by GHGs, direct and indirect effects of aerosols, and large volcanic eruptions. Our results suggest that GHG-induced aridification may be modulated regionally by future reductions in sulfate aerosol emissions.

尽管干旱对人类和自然系统造成了普遍影响，但对于区域干旱的大规模机制仍然知之甚少。在这里，我们使用多元方法^1,2从地球系统模型仿真的多个集合中识别两个不同的外部强制指纹。领先的指纹F _M1（x）的特征是全球变暖，湿干模式加剧^3，以及逐步进行的大规模大陆干旱化，其主要原因是温室气体（GHG）排放量增加了数十年。第二个指纹F _M2（x）捕获了明显的半球间温度对比^4,5，在热带辐合带^6,7,8,9的相关经向偏移以及与加利福尼亚¹⁰，萨赫勒^11,12和印度的降水和干旱异常相关。F _M2（x）表现出非线性的时间行为：由于半球形不对称硫酸盐气溶胶的排放增加，热带辐合带在1975年前向南移动，由于二氧化硫的排放减少和温室气体引起的北半球陆地变暖，1975年以后向北移动。在1950-2014年期间温度，降雨和干旱的联合变化观测中，这两个指纹在统计学上都是可识别的。我们表明，要对这些变化进行可靠的模拟，就需要结合温室气体强迫，气溶胶的直接和间接影响以及大火山爆发。我们的结果表明，GHG诱导的干旱化可能会受到未来硫酸盐气溶胶排放量减少的区域性调控。