In the Eocene of ~ 55 million years ago, the Earth had high levels of atmospheric CO2
, so studies of the Eocene can provide insights into the likely effects of present day fossil fuel burning. We ran a low-resolution but very fast climate model with 50 combinations of CO2
and orbital parameters, and an Eocene layout of the oceans and continents. Climatic effects of CO2
are dominant but precession and obliquity strongly influence monsoon rainfall and ocean-land temperature contrasts respectively.