Solar influence on the Indian summer monsoon during the Holocene

Abstract

The large (8%) changes in the past seasonal insolation have a well-documented influence on the Indian summer monsoon. However, the effect of the small ( < 1%) decade to century scale solar variability is less certain. Evidence is emerging that Earth's climate is sensitive to small changes in solar output on centennial time scale during the Holocene. Comparison of a recently published proxy record for sunspot activity with our newly-revised higher-resolution record of the Indian summer monsoon winds reveals multiple intervals of weak summer monsoon during the Holocene at multidecadal to centennial scales. Weak summer monsoon winds correlate with reduced solar output. Our results suggest that small changes in solar irradiance can bring pronounced changes in the tropical monsoon. The multidecade to century scale variations in the monsoon winds were much larger in the early Holocene coincident with increased sunspot numbers.