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.)
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|
|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|
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.
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© 2022 Patrik Erdes