The Role of Remaining Carbon Budgets and Net-Zero CO2 Targets in Climate Mitigation Policy

Purpose of Review Here, we review recent estimates of the remaining carbon budget, with a focus on characterizing key uncertainties and assessing the implications for net-zero CO2 targets and climate policy. Recent Findings Recent analyses offer a range estimates of remaining allowable CO2 emissions for the 1.5 degrees C and well-below 2 degrees C climate targets, though the treatment and coverage of key sources of uncertainty vary considerably among studies. We recommend that net-zero CO2 targets be set with explicit recognition of the uncertainty associated with carbon budget estimates and be updated regularly as this uncertainty is better constrained. Allocating the remaining carbon budget among countries or other entities, as well as monitoring progress at the subnational level, represents additional key challenges in applying a carbon budget framework to climate policy. Despite these challenges, recent advances in quantifying carbon budget uncertainty demonstrate that the concept is well-suited to inform climate policy and to evaluate whether net-zero CO2 targets are consistent with the goals of the Paris Agreement.