Mitigation choices impact carbon budget size compatible with low temperature goals

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 CO_2,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.