Relationship between Global Carbon Cycle and Climate Change during Cenozoic

Is CO₂ the Principal Cause of Long-term Climate Change?

Abstract

Climate change and variations of atmospheric CO₂ during Cenozoic have been discussed by many studies. The model results for global carbon cycle and climate change are generally consistent with those of many analytical studies concerning climate events in early Cenozoic, e.g., early Eocene warming events. However, the climate events proposed by analytical studies in late Cenozoic are not wholly inconsistent with the results of the model studies, e.g., Miocene climatic optimum (warming), cooling events in Eocene/Oligocene boundary and middle Miocene (15 Ma). Many problems remain in relation to evaluating CO₂ flux by hydrothermal solutions at mid-ocean ridges, island-arc, and back-arc basins in the models. Also, the discrepancy may be derived from errors in estimating weathering flux, organic carbon burial, and change in vegetation. Moreover, another greenhouse effect gas such as methane, land-sea distribution, albedo variations due to the formation of ice-sheets, and temperature distribution attributed to changes in the ocean circulation system should be considered. Recent analytical studies reveal that the CO₂ level since Miocene has remained relatively low in spite of the suggested climate events in this period. The mechanism of oceanic environmental change, as well as atmospheric CO₂, is especially important to elucidate climate change during Cenozoic.