The Eocene and the Earth’s Equator-Pole Temperature Gradient

Abstract: During the early Eocene, some 50 million years ago, the Earth was approximately 13°C warmer and the equator-to-pole surface temperature difference was much smaller than it is today. The overall warmth can more-or-less be understood by an increase in greenhouse gas content but the extremely warm winters in high latitudes over land have been problematic, and have led to proposals of a radical changes in atmospheric circulation.  We show that such exotic proposals are probably not needed, and that combinations of changes in surface albedo, cloudiness, and surface heat capacity of land can lead to simulations that are more-or-less within the uncertainty range of the majority of proxy data, including the reduced seasonality of Arctic land temperatures. However, the particular combination that actually occurred is still unknown. 

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