Hydroclimate insights from the warm Pliocene, Miocene, and Eocene

A warmer atmosphere holds more water vapor supporting an amplified hydrological cycle with both more intense precipitation events and droughts. Yet future climate projections are uncertain when it comes to predicting climatological changes in regional hydroclimate, particularly for subtropical and Mediterranean climates. Past warm climates in Earth's history offer an opportunity to learn how regional hydroclimate responds to global warming. Here we review insights from several studies that model and reconstruct hydroclimate during the warm climates of the Pliocene, Miocene and Eocene. A common finding is the importance of correctly predicting warming patterns and their impact on large-scale circulation, leading to circulation driven changes in climatological moisture convergence. Most notably, climate models that simulate the largest reduction in equator-to-pole temperature gradients are characterized by a reduction in subtropical moisture divergence, leading to an increase in mean annual precipitation and better agreement with proxy reconstructions.