Mitigation choices impact carbon budget size compatible with low temperature goals

Abstract

Global-mean temperature increase isroughly proportionalto cumulative emissions of carbon dioxide (CO2). Limiting global warming toany level thus implies a finite CO2budget. Due to geophysical uncertainties, the size of such budgets can only be expressed in probabilistic terms and is further influenced by non-CO2emissions. We here explore how societal choices related to energy demand and specific mitigation options influence the size of carbon budgets for meetingagiven temperature objective. We find that choices that exclude specific CO2mitigation technologies (like Carbon Capture and Storage) result in greater costs, smaller compatible CO2budgets until 2050, but larger CO2budgets until 2100. Vice versa, choices that lead to a larger CO2mitigation potential result in CO2budgets until 2100 that are smaller but can bemet at lower costs. Inmost cases, these budget variations canbe explained bythe amount of non-CO2mitigation that iscarried out in conjunction with CO2,and associated global carbon prices that also drive mitigation of non-CO2gases. Budget variations are of the order of 10% around their central value. In all cases, limiting warming to below 2 °Cthus still implies that CO2emissions needto bereduced rapidly inthe coming decades.