Significant Contribution of Paleogeography to Stratospheric Water Vapor Variations in the Past 250 Million Years

Stratospheric water vapor (SWV) variations play an important role in influencing the Earth's energy budget. Here, we investigate the SWV variations in the past 250 million years (Myr) using a fully coupled Earth System Model. It is found that both CO2 concentration and paleogeography have prominent influences on the SWV variations, while solar insolation plays a minor role. The SWV increases with surface warming and stratospheric moistening rate is accelerated during the warm periods in the past 250 Myr except for the Pangea supercontinent stage. The ratio of stratospheric moistening to surface warming is smaller in the warm Pangea supercontinent stage compared to that during the warm Cretaceous Period, which is due to the ascending and consequent cooling of the tropical tropopause layer associated with the severe surface warming over the tropical Pangea supercontinent. Our results suggest that paleogeography is an important factor in regulating SWV variations in deep-time climate.

Automated summary

CO2 concentrations and paleogeography significantly influence variations in stratospheric water vapor, while solar insolation plays a minor role. Except during the Pangea supercontinent stage, the stratospheric moistening rate is accelerated during warm periods in the past 250 million years.