The global CO2 budget runs out in 7 years

The remaining global CO2 budget to limit global warming to 1.5°C was given as 400 billion tonnes CO2 in the IPCC report of 2021.
For an average country, its share of this global CO2 budget will run out in 7 years.
For a high emission country such as the UK, its share of the carbon budget will run out in 2 years.
To stay within 1.5°C of global warming, immediate radical action is needed to phase out the burning of fossil fuels.

Atmospheric CO2 is now at a dangerous level

The CO2 released from burning fossil fuels persists in the atmosphere for thousands of years, and so the concentration of CO2 in the atmosphere has been steadily rising for the last 150 years, since large scale burning of fossil fuels commenced.

This is causing an increase in the average global temperature (now over 1°C), and more storms, floods, heatwaves and droughts - see document 51 and document 52.

We now realise that this is causing enormous numbers of deaths and climate refugees and a vast amount of environmental damage, and that there is an increasing risk of positive feedback loops - and that we must therefore make great efforts to limit global warming to 1.5°C.

What is the CO2 budget?

As the concentration of CO2 in the atmosphere increases, so does the average global temperature.

From the total amount of CO2 emitted by mankind in the past, and the effect it has had, scientists have estimated the limit to further emissions of CO2 if we are to keep global warming within a particular limit e.g. 1.5°C.

This is known as the CO2 budget (or carbon budget).

By comparing the CO2 budget with current annual CO2 emissions, we can calculate how long the budget will last if no changes are made. This indicates the degree of urgency of action.

The IPCC report of 2021

The AR6 WG1 report [1] was published by the Intergovernmental Panel on Climate Change (IPCC) in August 2021. (The IPCC is the United Nations body for assessing the science relating to climate change.)

The report includes figures for the CO2 budget for 1.5°C. The budget calculations had been adjusted slightly since the previous IPCC report of 2018, according to the further information available.

The residual global carbon budget to remain within 1.5°C of global warming with 67% probability is given as 400 billion tonnes CO2 from the start of 2020.

With the world population reaching 8 billion people within the next few years, this 400 billion tonnes works out as 50 tonnes CO2 per person.

Global CO2 emissions are about 36 billion tonnes per year (document 94), and so the 400 billion tonnes CO2 will last just 11 years if no reductions are made, i.e. the global CO2 budget for 1.5°C runs out at the end of 2030, i.e. in 7 years.

High emission countries

The Paris Agreement specifies in Article 4.1 that developed countries will have a proportionally higher reduction in emissions as it states "peaking [in greenhouse gas emissions] will take longer for developing countries", and states repeatedly that decisions will be taken according to "the principle of equity" - see document 122. This principle of equity is usually taken to mean that the residual global CO2 budget will be divided between nations as an equal share per person.

So if a country has CO2 emissions per person that are double the world average, it has to cut emissions twice as quickly as the average. If it cuts emissions only as fast as the average, it would take double its fair share of the CO2 budget.

The UK has CO2 emissions of about 8 tonnes per person per year (which is nearly double the world average of 4.5). So the UK's per capita fair share of the CO2 budget of 50 tonnes per person runs out in 6 years from the start of 2020, i.e. by the end of 2025, i.e. in 2 years time. Read more at document 33.

Most people are either unaware of or in denial about the severity and urgency of the climate emergency - read more at document 50.

Low emission countries

The Paris Agreement allows developing countries to continue to increase CO2 emissions for a period. Considering India as an example, its emissions are currently 1.8 tonnes CO2 per person per year, less than half the world average (see document 94). So India's share of the global CO2 budget of 50 tonnes per person will last about 30 years, and it has considerable leeway in its climate policies.

The global CO2 budget for 1.6°C and higher temperatures

For 1.6°C, the global CO2 budget is 150 billion tonnes more than the budget for 1.5°C. This will last the world an extra 4 years at the current global emission rate. For a high emission country such as the UK, its per capita share will last an extra 2 years at its current emission rate.

For higher temperatures, budgets increase in proportion, except that the risk of tipping points increases steadily.

Points from the UN / IPCC reports

Some key points from the IPCC report of 2021 are:

The relevant IPCC report prior to the 2021 AR6 WG1 report was the SR15 report [4][5][6], released by the IPCC in 2018. Some key points from this are:

Response by governments

After the 2019 street protests, which were sparked by the 2018 IPCC SR15 report, many national and local administrations declared a climate emergency, but most have since failed to implement the "rapid and far reaching transitions" recommended by the IPCC. Some governments, including the UK's, have even encouraged fossil fuel use by measures such as further road building.

In 2022, United Nations Secretary-General António Guterres took the extraordinary step of accusing governments of lying about climate action, saying "Some government and business leaders are saying one thing - but doing another. Simply put, they are lying". Read more at document 136.


[1]IPCC (Aug 2021) AR6 Climate Change 2021: The Physical Science Basis
[2]Secretary-General's statement on the IPCC Working Group 1 Report on the Physical Science Basis of the Sixth Assessment (Aug 2021)
[3]Abdalah Mokssit (Secretary of the IPCC) (Aug 2021) IPCC press conference
[4]IPCC (Oct 2018) SR15 report press release
[5]IPCC (Oct 2018) SR15 report headline statements
[6]IPCC (Oct 2018) SR15 Summary for policymakers

First published: Feb 2019
Last updated: 3 Nov 2023