State-dependence of Cenozoic thermal extremes

Abstract

Oxygen isotopes in sediments reflect Earth’s past temperature, revealing a cooling over the Cenozoic punctuated by multimillenial thermal extreme events. The magnitude of these extremes and their dependency on baseline climate state is not clearly understood. Here we use global records of deep sea foraminiferal δ18O as a proxy for atmospheric temperature over the Cenezoic and investigate how closely the generalised extreme value distribution matches δ18O block maxima. We find that the distribution of these extremes is captured well by the generalized extreme value distribution. In addition, the distribution of extremes’ shape changes with baseline temperature such that large thermal extremes are more likely in warmer climates. We therefore suggest that anthropogenic warming has the potential to return the baseline climate state to one where large thermal extremes are more likely.