Recent pronounced weakening of Asia summer monsoon over the past 450 years

Affecting a multitude of ecological and agricultural systems, the Asia summer monsoon (ASM) is essential for biodiversity and the food security of billions of people. Understanding past changes of the ASM is important for the detection and attribution of its recent evolution and future projection in the context of global warming. However, proxy-based, high-resolution reconstructions of the ASM prior to the period of instrumental measurements that started in the 1950s in China are still missing. Here, we use an ensemble of ten tree-ring width chronologies from the northern margin of the ASM to estimate ASM strength back to 1566 AD. The reconstruction not only reveals severe large-scale droughts in 1586/87 and 1759, but also negative anomalies during persistent locus plagues in the 1860s. The record also shows an unprecedented decrease in ASM since the mid-20^th century. Simulations from a coupled climate model suggest that the recent ASM decline could have been induced by increased anthropogenic aerosol emissions over the Northern Hemisphere.