No abstract

Earth's history has been characterised by complex interactions between life and the environment, which are often difficult to resolve. Here, we propose a new carbon cycle turbulence index (CT index ), based on the carbonate-carbon isotope (δ 13 C carb ) record, to measure the extent of environmental perturbation over the last billion years. The CT index trend is closely linked to Phanerozoic biotic extinction rates (ERs), as calculated from a palaeobiology database, supporting a strong environmental control on biotic ERs. We use the empirical CT index -ER relationship to compare the extent of environmental perturbation due to greenhouse gas emissions with that during the Permian-Triassic (PTr) transition (∼252 Ma), representing the most severe mass extinction of the Phanerozoic. At the current peak of fossil fuel emissions, the CT index indicates a moderate future environmental perturbation. However, if fossil fuel emissions increase into the next century, a pronounced CT index peak greater than that which occurred during the PTr transition is indicated, which suggests the potential for a severe "sixth mass extinction" in the future.