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.

Links

• The Carbon Budget - what is it and why is it important?, Grantham Institute
• Greta Thunberg has mentioned the 1.5ºC 420 GtCO₂ budget several times in her speeches.
• Kevin Anderson is a climate scientist with a focus on carbon budgets. He has been using carbon budgets as a way of setting goals on greenhouse gas emission reductions, e.g. for Järfälla kommun
• How much CO2 your country can still emit, in three simple steps, by Stefan Rahmstorf
• Carbon Emission Budget Calculator - another site that lets you calculate the remaining carbon emission budget for a country, by Florian Dierickx

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

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© 2022 Patrik Erdes