Environmental Science and Engineering Seminar

In almost all modern global climate models, greenhouse warming results in widespread reduction of soil moisture and strong increases in diagnosed drought, across the continental tropics, subtropics and midlatitudes.  This occurs because precipitation there does not change much, even as demand for evaporation is driven by the Clausius-Clapeyron equation to increase substantially.  Yet, past warm greenhouse climates (e.g. Cretaceous and Tertiary) were seemingly quite wet on the continents, and it is instead cold, low-GHG climates (e.g. the last glacial) that appear globally arid.  Is there a discrepancy between models and paleoclimates - and if so, why?  In this talk, I will review the extensive evidence for both the model and the paleoclimate behavior.  I will also describe several possible explanations for the difference along with planned work to test those explanations, including nonlinearity of the system, direct effects of CO₂ on vegetation, sea-level changes (of both cryospheric and solid-earth origin), continental movement, and wind stilling.  Finally, I will present recent idealized modeling results showing that greenhouse warming alone can cause a much wider range of terrestrial hydrologic responses than either the paleoclimates or the comprehensive GCMs would imply.