What are Carbon Budgets?

Human emissions of greenhouse gases are causing global warming. There is a strong relationship between the total amount of CO2 emitted to the atmosphere before achieving net zero emissions, and the total amount of warming achieved. A carbon budget is an amount of CO2 that can be emitted, while still limiting the warming to a specific number of degrees. To make sure a carbon budget does not overrun, net zero emissions must be achieved before the budget runs out.

The Paris Agreement state that the global temperature increase should be kept well below 2°C above pre-industrial levels and that efforts should be pursued to limit the temperature increase to 1.5°C above pre-industrial levels. The SR15 report shows clearly that the risks with 1.5°C of warming are lower than with 2.0°C. (There are still substantial risks even at 1.5°C of warming.)

IPCC Carbon budgets

Table 5.8 of the IPCC AR6 WGI report contain carbon budgets for different amounts of warming and different probabilities. These budgets have a start date of 2020-01-01. These budgets are used in the current version of this site.

Warming since 1850–1900 Probability
C F 17% 33% 50% 67% 83%
1.3º 2.3º 400 GtCO2 250 GtCO2 150 GtCO2 100 GtCO2 50 GtCO2
1.4º 2.5º 650 GtCO2 450 GtCO2 350 GtCO2 250 GtCO2 200 GtCO2
1.5º 2.7º 900 GtCO2 650 GtCO2 500 GtCO2 400 GtCO2 300 GtCO2
1.6º 2.9º 1200 GtCO2 850 GtCO2 650 GtCO2 550 GtCO2 400 GtCO2
1.7º 3.1º 1450 GtCO2 1050 GtCO2 850 GtCO2 700 GtCO2 550 GtCO2
1.8º 3.2º 1750 GtCO2 1250 GtCO2 1000 GtCO2 850 GtCO2 650 GtCO2
1.9º 3.4º 2000 GtCO2 1450 GtCO2 1200 GtCO2 1100 GtCO2 800 GtCO2
2.0º 3,6º 2300 GtCO2 1700 GtCO2 1350 GtCO2 1150 GtCO2 900 GtCO2
2.1º 3.8º 2550 GtCO2 1900 GtCO2 1500 GtCO2 1250 GCO2 1050 GtCO2
2.2º 4.0º 2850 GtCO2 2100 GtCO2 1700 GtCO2 1400 GtCO2 1150 GtCO2
2.3º 4.1º 3100 GtCO2 2300 GtCO2 1850 GtCO2 1550 GtCO2 1250 GtCO2
2.4º 4.3º 3350 GtCO2 2500 GtCO2 2050 GtCO2 1700 GtCO2 1400 GtCO2

Notes on calculations

Only the next 500 years (from 2020) are considered in any scenario.

The Global Fossil Carbon Budget (fossil fuels and cement production) is set to 90% of the Global Carbon Budget, since the land-use change part is estimated to be 10% of the total budget (GCP 2021), e.g. for a Global Carbon Budget of 400 GtCO2, the Global Fossil Carbon Budget is 360 GtCO2.


Global Carbon Budgets | Country Carbon Budgets | What are Carbon Budgets?

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