Pliocene climates from southwest North America and their implications for 21st century rainfall extremes (Invited Presentation)

Paleoclimate evidence from past warm climates can help us understand regional responses to higher greenhouse gas forcing. The mid Pliocene, an interval between roughly 3.3 and 3.0 million years ago, represents the last time that greenhouse gases were above 400 ppm. Molnar and Cane (2007) proposed, based on available paleoclimatic evidence, that changes in tropical SST in the equatorial Pacific, provide a template for understanding Pliocene hydroclimate changes. Since then, novel isotopic analyses of plant lipids have given us a more detailed view of regional hydroclimate change during the Pliocene. Our work from southwest North America suggests that the long-term evolution of southwest monsoon rainfall since the Pliocene is governed by changes in the gradient of temperature between the subtropics and tropics in the eastern Pacific. In the present day, similar changes are seen during multi-year marine heat waves on the California Margin. These oceanic extremes are tied to extremes in monsoon rainfall on land. Our results therefore suggest that the mean hydroclimate state of warm climates like the Pliocene show parallels with 21^st century extreme events. This emphasizes the fact that paleoclimate evidence can help reveal the ‘preferred patterns’ of regional SST change associated with terrestrial hydroclimate extremes.