The early Eocene period, about 50 million years ago, had a much warmer climate than today. It is possible to study this period with climate models, but to obtain a reasonable global match between model surface temperature and proxy reconstructions extremely high atmospheric CO2concentrations or a reduction in global cloud albedo is needed. In this work, these two methods are examined. The two simulations have an almost identical global-mean surface temperature and equator-to-pole temperature difference, but the atmospheric circulation and precipitation climate are quite different. This result provides a potential pathway for constraining the role played by CO2in making some periods of the deep past extremely warm.
Carlson, H. and Caballero, R.: Atmospheric circulation and hydroclimate impacts of alternative warming scenarios for the Eocene, Clim. Past, 13, 1037-1048, https://doi.org/10.5194/cp-13-1037-2017, 2017.
Figure The left panel shows the mean surface temperature in the model simulation using increased CO2 to model the Eocene period, the right panel show the difference in surface temperature pattern when cloud albedo is altered.