Climate Lessons from the Early Pliocene Warm Period
Four to five million years ago, in the early Pliocene epoch, Earth had a warm, temperate climate and carbon dioxide (CO2) concentrations similar to today’s, but with very different climate patterns. The gradual cooling that followed led to the establishment of modern temperature patterns, possibly in response to an atmospheric CO2 concentration reduction on the order of 100 parts per million, towards preindustrial values. In a new study, partly funded by the U.S. Department of Energy, a team of scientists synthesized the available geochemical proxy records of sea surface temperature. They found that, compared with today, the early Pliocene climate had much less change in temperature with latitude and longitude, but similar maximum ocean temperatures. Using an Earth system model, the authors show that none of the mechanisms currently proposed to explain Pliocene warmth can simultaneously reproduce all three of these crucial features. The authors suggest that a combination of several dynamical feedbacks currently underestimated in the models, such as those related to ocean mixing and cloud albedo, may have been responsible for these climate conditions. The study reinforces the need to improve constraints on cloud and ocean feedback systems.
Fedorov, A. V., C. M. Brierley, K. T. Lawrence, Z. Liu, P. S. Dekens, and A. C. Ravelo. 2013. “Patterns and Mechanisms of Early Pliocene Warmth, Nature 496, 43–49. DOI: 10.1038/nature12003.