About four years of emissions left for 1.5°C

A carbon budget is the total amount of CO₂ the world can still emit while keeping warming below a chosen limit. It turns an abstract temperature goal into a concrete accounting problem — and the ledger is running low.

The numbers

From the start of 2025, the Global Carbon Project estimates the remaining budgets (for a 50% chance) at roughly:

• 1.5°C: ~170 Gt CO₂ — about 4 years at current rates.
• 1.7°C: ~525 Gt — about 12 years.
• 2.0°C: ~1,055 Gt — about 25 years.

With fossil emissions at a record 38.1 Gt in 2025, the 1.5°C budget is, in the project's words, “virtually exhausted.”

Large uncertainty, clear direction

These are central estimates with wide error bars — hundreds of gigatonnes — because they depend on climate sensitivity and non-CO₂ gases. But the direction is unambiguous: every year of record emissions shrinks the budget, and the remaining room for 1.5°C is now measured in a handful of years.

What the budget implies

Staying within any limit ultimately requires emissions to reach net zero; the budget simply sets how fast. It reframes climate action as a fixed, depleting resource — which is why it is among the most policy-relevant numbers in all of environmental science.