
Carbon budget calculations for the average country
An "average country" of the world is used here as an example of emission cuts that are needed in order to comply with the Paris Agreement and other aspirations to limit global warming to 1.5°C.
The web page shows a series of carbon budget calculations.
The average country
This is taken to have- a population equal to the world average country population of 40 million in 2021
- CO2 emissions in 2019 equal to the world average of 4.6 tonnes per person per year (this world average has changed little for several decades, unlike the world total which has increased steadily, as the world population has grown)
- emissions resulting from the production of imports equal to the emissions from the production of exports.
Options for limiting global warming to 1.5°C
The scientific consensus is that global warming can be limited to 1.5°C if emissions since the start of 2020 are limited to 400 billion tonnes CO2 (this is with 67% confidence). This works out as 50 tonnes per person. This is a lifetime limit.The average country has already used 23 tonnes of this per person budget in the 5 years to the end of 2024, leaving a residual budget from the start of 2025 of 27 tonnes CO2 per person.
The charts shown below have been generated by the calculator at carbonindependent.org/carbonbudgets.php, and they can be replicated there.
1: Constant emissions: not compliant

Clearly, CO2 emissions need to be reduced.
2: Net Zero 2050 (linear decline): not compliant with the carbon budget

One version of net zero 2050 is to cut emissions steadily, by the same amount each year, which gives a sloping straight line on a chart of annual emissions. This can be termed "linear decline". It is easy to calculate that such a pathway of emissions would extend the carbon budget by 1 year to 2031, and so the pathway would not be compliant with the residual carbon budget. It would in fact emit 50% more CO2 than the carbon budget of 50 tonnes per person.
3: Net Zero 2040 (linear decline): not compliant with the carbon budget

4: Compliant Net Zero (linear decline): Net Zero 2037

Calculations show that for an average country, emissions need to be cut to zero in 2037 if a linear decline.
5: Compliant exponential decline pathway

6: Compliant smoothed exponential decline pathway

Options for limiting global warming to temperatures higher than 1.5°C
7: Compliant smoothed exponential decline - 1.6°C

Showing renewable energy
8: Showing renewable energy with linear extrapolation

This can be shown on a carbon budget chart via the amount of CO2 that would have been emitted if the energy had been produced from fossil fuels.
One possible scenario is that energy from renewable sources continues to increase at the same rate as it has done over recent years. This is termed a linear increase, and is shown on the chart.
9: Showing renewable energy with exponential extrapolation

First published: 22 Dec 2023