LAUSR

The Miocene Climatic Optimum (MCO) from ~17 to 14 million years ago (Ma) represents an enigmatic reversal in Cenozoic cooling. A synthesis of marine paleotemperature records shows that the MCO was a local maximum in global sea surface temperature superimposed on a period from at least 19 Ma to 10 Ma, during which global temperatures were on the order of 10°C warmer than at present. Our high-resolution global reconstruction of ocean crustal production, a proxy for tectonic degassing of carbon, suggests that crustal production rates were ~35% higher than modern rates until ~14 Ma, when production began to decline steeply along with global temperatures. The magnitude and timing of the inferred changes in tectonic degassing can account for the majority of long-term ice sheet and global temperature evolution since 20 Ma. Description Crustal effects on climate Why was the long-term global cooling trend of the Cenozoic interrupted by a several-million-year interval of warming during the middle of the Miocene? Herbert et al. present a reconstruction of global ocean crustal production to show that tectonic degassing of carbon can account for most of the long-term ice sheet and global temperature evolution for the past 20 million years (see the Perspective by von der Heydt). These results provide further support for the idea that sea floor spreading rates can control global changes in climate. —HJS Changes in plate tectonics drove degassing of carbon dioxide and global temperatures over the past 20 million years.