Anthropogenic aerosols are a potential cause for migration of the summer monsoon rain belt in China

It has been proposed that the current and future global warming caused by increased greenhouse gases can produce a northward shift of the Earth’s rain belt (1). This conclusion is supported by a recent study in PNAS by Yang et al. (2) in which the carbon isotope composition of 21 loess-soil sections from the Chinese Loess Plateau for the past 20 ka have been systematically investigated. The authors concluded that at least a 300 km northwestward migration of the monsoon rain belt had occurred from the cold Last Glacial Maximum (LGM) to the warm Holocene in China on the basis of the spatiotemporal patterns of C₄ plant biomass. The authors further imply that the observed southern drift of the summer monsoon rain belt in China during the past few decades will reverse itself and migrate north with the continuation of global warming.

However, Yang et al.’s (2) conclusion fails to consider climate effects of anthropogenic aerosols, a critically important factor for the recent southward migration of the summer monsoon rain belt in China (3⇓⇓–6). The climate model experiments reveal that the observed widespread decrease of summer monsoon rain over South Asia can be attributed mainly to …

↵¹To whom correspondence may be addressed. Email: shaocaiyu{at}zju.edu.cn or alapaty.kiran{at}epa.gov.