How Well Do We Understand the Geological Carbon Cycle?

The foundation of our understanding of the geological carbon cycle, and how this acts as Earth’s “thermostat,” was articulated in a seminal paper in 1981 (Walker et al). They suggested that silicate weathering on the continents acts as a stabilizing feedback on the carbon cycle such that increased atmospheric pCO₂ leads to increased weathering rates and hence increased removal of CO₂ from the atmosphere. This “textbook model” is at the core of most models of long-term biogeochemical cycles. We summarize evidence that there are many other processes in the geological carbon cycle that may be equally or more important than those in the Walker model. We argue there is a need to move beyond the textbook model in both teaching and research.