Reduction in Himalayan snow accumulation and weakening of the trade winds over the Pacific since the 1840s

In 1884, Blanford suggested that summer rainfall over Northwest India was anti-correlated with snow cover during the preceding winter and spring in the western Himalaya. Walker elaborated on this suggestion in his seminal work on predictors of the Indian summer monsoon, a body of work that forms the basis of our understanding of how Eurasia influences this monsoonal circulation. Recently, a number of studies have questioned the existence of this relationship or have proposed a more complex coupling between Eurasian snow cover, including the Himalaya, and the Indian summer monsoon. Here, we present a 196-year record of snow accumulation from a Himalayan ice core that contains a decreasing trend in accumulation that began in the 1840s. Indian summer monsoon rainfall shows no evidence of such a trend and we argue that this reduction in snow accumulation is associated with a long-term weakening of the trade winds over the Pacific Ocean.