RADIATIVE FORCING BY NON-CO2 GREENHOUSE GASES IN THE EARLY EOCENE

Methane (CH4), ozone (O3) and nitrous oxide (N2O) are the three most important greenhouse gases (GHGs) in the lower atmosphere after carbon dioxide and water vapour. Polar ice cores show CH4 and N2O underwent significant variations in phase with climatic change on glacial-interglacial timescales. The expectation therefore is that the concentration of these non-CO2 GHGs was higher at times in the past when the climate was considerably warmer than even the warmest interglacial. This presentation will describe new results from an 'Earth system' model that includes trace gas emissions from the biosphere and atmospheric chemistry calculations for the early Eocene. The feedback of the calculated non-CO2 GHG concentrations on the Eocene climate is examined the compared with data from the geological record. We conclude that non-CO2 GHG represent a significant missing component of climate modelling studies in past warm climates.