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 IPCC special report on global warming of 1.5ºC (SR15) state that the budget to limit warming to 1.5°C above pre-industrial (1850-1900) levels with a 66% probability is 420 GtCO2. (1 GtCO2 = 1 billion tonnes (metric tons) CO2.)
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 2.2 of SR15 contain carbon budgets for different amounts of warming and different probabilities. These budgets have a start date of 2018-01-01. The emissions in 2018 reduced the budget by 42 ± 3 GtCO2 per year.
|Warming since 1850–1900||Probability|
|1.5º||2.7º||840 GtCO2||580 GtCO2||420 GtCO2|
|1.6º||2.88º||1080 GtCO2||770 GtCO2||570 GtCO2|
|1.75º||3.15º||1440 GtCO2||1040 GtCO2||800 GtCO2|
|2.0º||3.6º||2030 GtCO2||1500 GtCO2||1170 GtCO2|
These IPCC budgets are the carbon budgets used on this site.
Only the next 500 years (from 2018) are considered in any scenario.
The Equitable Country Carbon Budget (fossil fuels and cement production) value is calculated by multiplying the Equitable Country Carbon Budget by the total amount of global emissions from fossil fuels and cement production (34741 MtCO2) divided by the total global CO2 emissions (42000 MtCO2).
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© 2020 Patrik Erdes