Carbon budget

A carbon budget is the total amount of carbon dioxide the world can still emit while keeping warming below a chosen limit. In other words, it turns a temperature goal — such as the Paris Agreement's aim of holding warming to 1.5°C — into a finite quota of emissions that human activity is allowed to release.

How much is left?

The highest-level estimates of the world's carbon budget come from the UN's climate science panel, the IPCC, together with the Global Carbon Project. Their assessments show that the remaining budget for 1.5°C is small and nearly exhausted — on the order of 130–170 billion tonnes of CO₂ from 2025, only about four years of emissions at current rates. The budget for limiting warming to 1.7°C is roughly 525 billion tonnes (around twelve years), and for 2°C about 1,055 billion tonnes (around twenty-five years). With the world emitting close to 40 billion tonnes a year, current emissions far outpace these limits.

Different levels

Individuals, municipalities and — above all — countries can all work to a carbon budget. The global figure is set by climate science; national and personal budgets are then shares of that total. Comparing a country's or a person's actual emissions against their budget shows how far off track they are.

What it means

Used well, the remaining budget should fund the transition from a high-emission society to a low-emission one — making activities far more efficient so they emit very little. Because the budget consistent with 1.5°C is now so small, climate scenarios increasingly rely on negative emissions, removing CO₂ from the atmosphere through technologies such as carbon capture and storage (CCS), to stay within safe limits.

Sources: Global Carbon Project & IPCC — Global Carbon Budget 2025 FAQs