NASA - National Aeronautics and Space Administration

Holocene climate proxies suggest substantial correlations between tropical meteorology and solar variations, but these have thus far not been explained. Using a coupled ocean-atmosphere-composition model forced by sustained multi-decadal irradiance increases, we show that greater tropical temperatures alter the hydrologic cycle, enhancing the climatological precipitation maxima in the tropics while drying the subtropical subsidence regions. The shift is enhanced by tropopause region ozone increases, and the model captures the pattern inferred from paleoclimate records. The physical process we describe likely affected past civilizations, including the Maya, Moche, and Ancestral Puebloans who experienced drought coincident with increased irradiance during the late medieval ($900 – 1250). Similarly, decreased irradiance may have affected cultures via a weakened monsoon during the Little Ice Age ($1400– 1750). Projections of 21st-century climate change yield hydrologic cycle changes via similar processes, suggesting a strong likelihood of increased subtropical drought as climate warms.