Characteristics of variations of climate change and atmospheric CO2 concentration at different time scales over the past 500 Ma

Abstract:

It is generally believed that current global warming is due to the persistent rise of atmospheric greenhouse gas CO₂. The consensus is based mostly on the observational data of past decades and the polar ice core records. To understand the relationship between climate change and atmospheric CO₂, their behaviors over a longer interval at different time scales need to be appreciated. Here, we collect and analyze past 500 Ma records of atmospheric CO₂ and temperature in six time periods, namely Phanerozoic, Cenozoic, middle Pleistocene, last deglaciation, past millennium, and recent decades. According to the carriers and time spans, we divide these records into three categories: 1.The millionaire and longer records from model calculation and paleosols/paleobotany proxies. Although the trends of both variables are generally consistent on this time scale, it is difficult to establish a clear causal relationship because of great uncertainties and low resolutions of both sets of data. 2.The orbital scale mainly from the polar ice core. High precise CO₂ and temperature reconstructions allow for an examination of the possible role of atmospheric CO₂ in the glacial-interglacial transformation. 3.The records at centennial and shorter time scales over the past millennium from ice, snow, and instrumental data. The past millennium records are most abundant and accurate, especially CO₂ has been measured directly in recent decades. However, due to the difficulties in distinguishing the effect of CO₂ from other factors, there are great uncertainties in the interpretation of climate change versus CO₂. Overall, we come to the following conclusions:1.Paleoclimatic reconstructions show that both temperature and atmospheric CO₂ have generally decreased over the past 500 Ma. However, there are no consistent sequential orders in the changes between these two variables. 2.The Earth’s atmospheric CO₂ has a drastic oscillation history. There were many high CO₂ periods when the values were higher than 5000 ppm, and there are several low CO₂ periods when the values dropped to less than 100 ppm. 3.According to global observational data, atmospheric CO₂ has recently exceeded 400 ppm. Although there is no conclusive evidence that shows this value has a special significance, it is the highest since the last 800 ka, and rare over the Quaternary.