How much more carbon can we burn and still stay under 1.5 °C?
Warming tracks one running total remarkably well: all the carbon dioxide humanity has emitted since 1750. At the start of 2026, about four years' worth was left for 1.5 °C.
▶ Start the storyVery little, by the latest estimates. Warming follows one running total remarkably well: all the carbon dioxide humanity has emitted since 1750. Temperature rises roughly in a straight line with that total. It hardly matters where the CO2 came from, and largely not when it was released. That is what makes a carbon budget possible: the most CO2 that can still be emitted for a given warming limit.
Humanity had emitted about 2,390 billion tonnes of CO2 by 2019. Each extra 180 billion tonnes or so adds about 0.1 °C. By 2024, human activity had warmed the planet by about 1.36 °C.
The Global Carbon Budget 2025 estimates that about 170 billion tonnes remained at the start of 2026, for a 50 percent chance of staying under 1.5 °C. That is around four years at the 2025 rate. For 2 °C, about 1,055 billion tonnes remained, or around 25 years. These figures are uncertain: depending on how much other gases like methane are cut, the budget can be about 220 billion tonnes larger or smaller.
Remaining carbon budget (from January 2026, 50% chance)
years of current emissions
| Years remaining | |
|---|---|
| 1.5 °C | 4 years of current emissions |
| 1.7 °C | 12 years of current emissions |
| 2 °C | 25 years of current emissions |
Four years does not mean four years left to act. It means the budget would be used up in about four years if emissions stayed flat. It has shrunk fast: in early 2022 it was put at about 420 billion tonnes, or 11 years.
Because warming tracks the total, it is expected to slow sharply once emissions reach net zero, the point where emissions and removals balance. Getting there means deep cuts, such as moving from fossil fuels to clean energy and halting deforestation. Only a small remainder would be offset by removing carbon. By late 2023, about 145 countries, covering close to 90 percent of emissions, had announced or were considering net zero targets. One of the scientists working on these questions, Oxford's Myles Allen, also started climateprediction.net, which runs climate models on computers lent by the public.
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Recap
Net zero, where emissions and removals balance, is the point at which CO2-driven warming is expected to slow sharply; about 145 countries had announced or were considering net zero targets by late 2023.
Surprising fact · Each extra 180 billion tonnes or so of CO2 adds about 0.1 °C of warming, whenever it is emitted.
Connects to
- ⚖️ Could the climate pass a point of no return?
- 📊 How much warmer will Earth get if we double its carbon dioxide?
- 🌋 Could humans cool the planet by copying what a volcano does?
- 🌍 How did one treaty get ratified by every country in the UN?
- 🏭 Why do free markets make too much pollution, and can a price fix it?
Sources (5)
No source, no claim. Every fact in this lesson (21 claims) cites at least one of these.