COP31 and the Overshoot Debate: Why the Carbon Budget and Historical Responsibility Still Matter
As COP31 (the 31st yearly UN climate conference) begins in Antalya, Türkiye, an expert analysis argues that the new talk of "overshoot" must not become a replacement for real cuts in emissions.
"Overshoot" means global warming going above the 1.5°C limit for some years and then being pulled back down later. Recent UN analysis treats an "overshoot, peak and decline" path as the best option still left, because the world is set to cross 1.5°C.
The analysis points out that no COP decision has ever written down the actual number (in tonnes) for the total or remaining carbon budget. The carbon budget is the total amount of carbon dioxide (CO2) the world can still release while staying within a warming limit.
It also notes that COP decisions have never discussed which countries have already used up most of that budget through their past emissions.
The analysis says that if COP31 is to give real push to climate action, its decisions must go back to the basics: the size of the carbon budget and a fair sharing of it between rich and developing countries.
Carbon Budget: Historical Emissions and the Idea of Carbon Debt
A carbon budget is the total amount of carbon dioxide that all of humanity can still release if we want to keep warming below a chosen limit, like 1.5°C. It works like a fixed family budget: every tonne spent is gone for good. Scientists found that warming depends on the total CO2 released over time, not on any one year's emissions. So the question "who has already used the budget?" becomes a question of fairness between countries.
The analysis argues that COP decisions talk about 1.5°C but avoid the hard number behind it: how many tonnes of CO2 are left, and who used up the rest. Putting the carbon budget back at the centre of COP31 would show clearly how much room is left and how unequally it has been used.
Overshoot Pathways in Climate Science
An overshoot happens when global warming goes above a chosen limit, such as 1.5°C, for some time and is then brought back below it later. An overshoot pathway is a plan for how emissions could move so that warming first crosses the limit, reaches a peak, and then falls. Bringing the temperature down needs net-negative emissions, which means taking more CO2 out of the air than we put in.
The analysis warns that the "overshoot" story is being used as if going past 1.5°C were a planned and safe step. Its point is that overshoot planning cannot replace deep and fast emission cuts now, because removals later are uncertain and costly.
Common but Differentiated Responsibilities and Respective Capabilities (CBDR-RC)
Common but Differentiated Responsibilities and Respective Capabilities, or CBDR-RC, is a basic principle of global climate law. It says all countries share the duty to protect the climate, but not all must do the same amount. Rich countries polluted the most in the past and have more money and technology, so they must lead. Developing countries like India must also act, but according to their own ability and needs.
The analysis says COP decisions have never discussed which countries spent most of the carbon budget. Linking the carbon budget to past emissions is exactly how CBDR-RC turns into numbers: those who used the most should cut the most and help the rest.
- COP31: Antalya, Türkiye, 9 to 20 November 2026; Türkiye hosts while Australia leads the negotiations.
- Remaining 1.5°C carbon budget: about 130 GtCO2 from the start of 2025 (Indicators of Global Climate Change, June 2025).
- IPCC AR6 (2021): about 500 GtCO2 remaining from 2020 for a 50% chance of 1.5°C; about 2,390 GtCO2 emitted between 1850 and 2019.
- COP28 Global Stocktake (2023): past emissions already used about four-fifths of the total 1.5°C budget.
- "Limited overshoot" (IPCC): exceeding 1.5°C by up to about 0.1°C.
- CBDR-RC: Article 3.1 of UNFCCC (1992); Principle 7 of the Rio Declaration.