Speaker: Professor Geoffrey Vallis from University of Exeter

Title: "Trying to Demystify Hothouse Climates"

Abstract: Earth has gone through various periods with very warm climates and may again in the future. Although the overall temperature increases are most likely caused by very high levels of greenhouse gases, difficulties remain in understanding changes on regional and seasonal scales. In particular, the apparently very low equator-pole temperature gradient of the Eocene, and the very warm winters at high latitudes even over land surfaces, bring into question our understanding of the climate feedbacks and general circulation itself. Here we show, using an idealized numerical model in conjunction with basic physical arguments, that many of these features can be explained with plausible, known, physical processes. Although we cannot yet be certain which of these processes is dominant, and a full agreement with proxy data is elusive, it seems that we may be getting closer to a reasonable understanding. (Joint work with Matthew Henry.)