Driving force behind global cooling in the Cenozoic: an ongoing mystery

The stepwise cooling marks the long-time global climate change during the Cenozoic, particularly since the Oligocene/Eocene boundary. This climatic evolution has been punctuated by several warming such as the peak Cenozoic warmth at 52 Ma, the late Oligocene warming at ∼25 Ma and the Mid-Miocene Climatic Optimum at 17-14 Ma. Concurring with the global temperature changes, the Asian paleoenvironment has been modulated by the global cooling and the tectonic uplift during the Cenozoic, but what have driven the global climatic changes remains unresolved. In this review paper, I hypothesize that a threshold CO2 level in combination with favorable orbital configuration, ocean circulation, enhanced ice albedo and possible roles of silicate mineral and basalt weathering together facilitated the development of glaciations in the Cenozoic and the past temperature change. The synchronous variations between Earth's surface temperature and atmospheric CO2 level may indicate that the atmospheric CO2 content is the direct driving force for the global climatic cooling, but this hypothesis needs testing by using high-resolution geological record and paleoclimatic modeling.