What is a carbon budget, and how does it relate to staying below a global temperature target?

• A. A carbon budget is the total amount of CO2 that can be emitted while keeping warming below a target; emissions accumulate to exhaust that budget.
• B. A carbon budget is the amount of carbon stored in forests.
• C. A carbon budget is the funding allocated to carbon capture technologies.
• D. A carbon budget is the cap on all greenhouse gas emissions regardless of warming.

Answer: (C)

A carbon budget is the total amount of CO2 the world can emit while keeping global warming below a chosen temperature limit. Emissions accumulate over time, so every ton released toward the atmosphere uses up part of that budget. Once the budget is exhausted, continuing to emit makes it very likely that the target will be surpassed unless there are substantial removals or the target is adjusted. This concept directly links to staying within a temperature goal: tighter targets correspond to smaller budgets and hence faster, deeper reductions in fossil fuel use and related emissions. It’s not about how much carbon is stored in forests, nor about funding for carbon capture, nor a blanket cap on all greenhouse gases. Budgets are typically expressed in CO2-equivalents and depend on factors like climate sensitivity and non-CO2 climate forcings, shaping how much room we have for emissions now and in the future.