What Models Tell Us About the Evolution of Carbon Sources and Sinks over the Phanerozoic

The current rapid increase in atmospheric CO2, linked to the massive use of fossil fuels, will have major consequences for our climate and for living organisms. To understand what is happening today, it is informative to look at the past. The evolution of the carbon cycle, coupled with that of the past climate system and the other coupled elemental cycles, is explored in the field, in the laboratory, and with the help of numerical modeling. The objective of numerical modeling is to be able to provide a quantification of the processes at work on our planet. Of course, we must remain aware that a numerical model, however complex, will never include all the relevant processes, impacts, and consequences because nature is complex and not all the processes are known. This makes models uncertain. We are still at the beginning of the exploration of the deep-time Earth. In the present contribution, we review some crucial events in coupled Earth-climate-biosphere evolution over the past 540 million years, focusing on the models that have been developed and what their results suggest. For most of these events, the causes are complex and we are not able to conclusively pinpoint all causal relationships and feedbacks in the Earth system. This remains a largely open scientific field.