The UK's share of the global CO2 budget runs out in 2 years

The remaining global CO2 budget to keep global warming within 1.5°C was estimated as 400 billion tonnes CO2 in the IPCC report of 2021.

The UK's per capita share of this global CO2 budget will run out in 2 years (at the end of 2024).

This timescale is very far from what UK citizens have been led to believe, so the calculations are set out here in detail so that readers can decide for themselves.

To stay within 1.5°C of global warming, immediate radical action is needed to phase out the burning of fossil fuels.

What is the CO2 budget?

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).

As the concentration of CO2 in the atmosphere increases, so does the average global temperature. There is a scientific consensus that we must make great efforts to limit global warming to 1.5°C - see document 54.

From the total amount of CO2 emitted by mankind in the past, and the effect it has had, we can estimate 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 UK's CO2 budget for 1.5°C

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 calculations
Table SPM.2 of reference [1]
The mathematics are simple, but the conclusion of a timescale of 2 years is so far from what is being discussed that the calculations are set out here in detail, so that readers can decide for themselves.

1. The global CO2 budget to remain within 1.5°C of global warming with 67% confidence is given as 400 billion tonnes CO2 from the start of 2020. This is given in Table SPM.2 on page 38 of the report (reproduced here).

2. Dividing the 400 billion tonnes CO2 between the 8 billion world population gives 50 tonnes CO2 per person as a personal lifetime CO2 budget.

3. Since the UK's emissions are around 10 tonnes CO2 per person per year (document 23), the UK's per capita share will last 5 years from January 2020, that is until December 2024 - just 2 years away.

Most people are either unaware or in denial about the severity and urgency of the climate emergency.

Why the 2-year timescale should be common knowledge

Confirmation from other sources on CO2 budgets

1. Zero carbon sooner (updated 2021) is a working paper from the Centre for the Understanding of Sustainable Prosperity at Surrey University [3] [4].

This also concludes (in its preferred analysis - see chart) that the UK's fair share of the remaining global CO2 budget will run out in 2 years - see document 128.

2. The Tyndall Centre reports: The Tyndall Centre for Climate Change Research at the University of Manchester published similar calculations in 2019 in reports for each UK local authority [5]. For example, the report for Wirral Council [6] showed that annual cuts in emissions of 13% were needed (with the lack of action, faster cuts are now required). Figure 1 of the report ("Pathway projections for Wirral"), showing the rapid cuts, is reproduced here.

3. Carbon budget calculator

Why the 2-year timescale is not common knowledge

Alternatives to keeping within the UK's per capita share of the CO2 budget for 1.5°C.

If we choose not to keep the UK's total emissions within its per capita share of the global CO2 budget for 1.5°C, there are other options. These all result in additional harm to vulnerable people. Options are

The UK's 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. The UK's per capita share will last an extra 2 years at its current emissions rate.

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

Related documents

The main points on this page have also been published:


[1]IPCC (Aug 2021) AR6 Climate Change 2021: The Physical Science Basis (downloaded 21 Aug 2021) or
[2]IPCC (Oct 2018) SR15 Summary for policymakers
[4] Jackson T (2021) Zero Carbon Sooner: Revised case for an early zero carbon target for the UK. CUSP Working Paper No 29. Guildford: University of Surrey.
[5]Tyndall Centre (2019) The Tyndall carbon budget tool
[6]Tyndall Centre (2019) Setting Climate Commitments for Wirral
[7]Turning delusion into climate action - Prof Kevin Anderson, an interview (2020) Responsible Science

First published: 28 Sep 2021
Last updated: 4 May 2023