Emissions cessation yields multi-century cooling

Abstract

Predicting the long-term warming commitment from past emissions is hindered by a lack of consensus amongst climate models. As a result, there is very low confidence that reaching net-zero emissions in the coming decades will stabilize the temperature beyond the 21st century. Here we provide a novel means of inferring the multi-century warming commitment directly from observations and established climate metrics. We cease emissions of all greenhouse gases and aerosols, and quantify the post-emissions temperature change by comparing the disequilibrium in the carbon system to the disequilibrium in the ocean’s thermodynamics. Constraining these disequilibria yields a prediction of multi-century cooling of approximately −0.4°C if emissions presently cease. For future emissions pathways, similar constraints indicate multi-century cooling after net-zero. Relative to the peak temperatures at net-zero, idealized theory and climate models of reduced and intermediate complexity predict a long-term decrease of −0.7 to −1.0°C depending on the scenario. These findings build confidence that net-zero mitigation pathways yield declining temperatures beyond the 21st century.