CO2Budgets

CO2Budgets refers to the framework for quantifying the maximum cumulative emissions of carbon dioxide (CO2) allowed into the atmosphere to meet a specified climate target, typically a limit on global average temperature rise relative to pre-industrial levels. The concept rests on the fact that CO2 persists in the atmosphere for long periods and that total cumulative emissions are a primary driver of long‑term warming.

Global carbon budgets are commonly expressed in gigatonnes of CO2 (GtCO2) and are linked to targets such as 1.5°C or 2°C of warming with a given probability. Budgets are estimated using climate models and observations, incorporating uncertainties in climate sensitivity, the carbon cycle, and non-CO2 forcings. As emissions accumulate, the remaining budget declines, making rapid reductions essential for pathways that aim to keep warming within the chosen target. In many assessments, meeting a 1.5°C goal would require near‑term reductions and, in some scenarios, the deployment of negative emissions later to offset residual emissions.

Budgets can be conceptually allocated across regions or sectors, and equity considerations—such as per‑capita rights and historical responsibility—inform discussions of fair shares. They are used to guide mitigation pledges, inform policy design, and support long‑term planning toward net‑zero emissions by mid‑century.

Limitations include dependence on uncertain future forcings and climate responses, the treatment of non‑CO2 effects, and the possibility of overshoot scenarios that require substantial CO2 removal to remain within targets. Despite uncertainties, CO2Budgets provide a transparent framework for communicating the scale of action needed to meet climate objectives.