Anthropogenic aerosols mask increases in US rainfall by greenhouse gases

Daily rainfall accumulations are a critical component of the global water cycle, and comprehensive understanding of human-induced changes in rainfall is essential for water resource management and infrastructure design. Detection and attribution methods reveal cause and effect relationships between anthropogenic forcings and changes in daily precipitation by comparing observed changes with those from climate models. However, at regional scales, existing studies are rarely able to conclusively identify human influence on precipitation. Here we show that anthropogenic aerosol and greenhouse gas emissions are the primary drivers of precipitation change over the United States and, by simultaneously accounting for both agents, we explicitly decompose the uncertain regional human influence into isolated components. At the scale of the United States, individual climate models reproduce observed changes due to anthropogenic forcing but cannot confidently determine whether each emissions source increases or decreases rainfall. Our results show that conflicting literature on trends in precipitation over the historical record can be explained by offsetting equal and opposite aerosol and greenhouse gas signals.