Response of the hydrological cycle to orbital and greenhouse gas forcing

Abstract

The sensitivity of the hydrological cycle to changes in orbital forcing and atmospheric greenhouse gas (GHG) concentrations is assessed using a fully coupled atmosphere‐ocean‐sea ice general circulation model (Kiel Climate Model). An orbitally‐induced intensification of the summer monsoon circulation during the Holocene and Eemian drives enhanced water vapor advection into the Northern Hemisphere, thereby enhancing the rate of water vapor changes by about 30% relative to the rate given by the Clausius‐Clapeyron Equation, assuming constant relative humidity. Orbitally‐induced changes in hemispheric‐mean precipitation are fully attributed to inter‐hemispheric water vapor exchange in contrast to a GHG forced warming, where enhanced precipitation is caused by increased both the moisture advection and evaporation. When considering the future climate on millennial time scales, both forcings combined are expected to exert a strong effect.