The amount of rain in South Asia during the summer months is influenced by changes in sea surface temperatures worldwide. By studying different climate models, scientists found that about half of the year-to-year variation in monsoon rainfall can be explained by these temperature changes. This impact is mainly due to how sea surface temperatures affect the movement of air in the atmosphere, rather than just the amount of water vapor in the air. The temperatures in the tropical Pacific Ocean have a bigger effect on the rainfall variability than those in the Indian Ocean.