Early Miocene CO2 estimates from a Neotropical fossil leaf assemblage exceed 400 ppm

PREMISE OF THE STUDY: The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO2 records for this interval suggest paradoxically low concentrations ( 95% confidence) that CO2 during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO2 concentration at this time, more in keeping with a CO2 -forced greenhouse climate.