Paleobotanical Evidence for Near Present-Day Levels of Atmospheric CO sub(2) During Part of the Tertiary

Most research investigating the paleoclimate is based on contemporary understanding of the relationship between carbon dioxide, a potent greenhouse gas, and the temperature of the planet. These issues are also critical for the development of accurate estimates of expected future warming. Researchers used the inverse relationship between leaf stomatal indices and the partial pressure of CO sub(2) in modern Ginkgo biloba and Metasequoia glyptostroboides to establish a reconstruction of historical CO sub(2) levels based on fossilized samples of Ginkgo and Metasequoia cuticles for the middle Paleocene to early Eocene and middle Miocene. Findings indicated that other factors beside CO sub(2) caused historical periods of global warming.