The UK's share of the global carbon budget will be used up in just over 3 years

As Boris Johnson, at the UN, calls on other countries to take more action on the climate, Dr Ian Campbell examines what the science is really saying about the scale of carbon emissions reduction needed by the UK to comply with the Paris Agreement.

Responsible Science blog, 24 September 2021

How urgent is an ‘emergency’? The word usually implies that immediate action is needed, but in the 2 years since the declarations of a climate emergency by many national and local administrations following the 2019 street protests, there has been little effective action. In some countries, e.g. the UK, fossil fuel use has even been encouraged by measures such as further road building. It is all a long way from the “rapid and far-reaching transitions”, taking just a few years, that was envisaged by the 2018 Special Report of the Intergovernmental Panel on Climate Change (IPCC), [1] which sparked the street protests.

We can quantify the urgency of the climate emergency in terms of the residual carbon budget - i.e. how much more CO2 can be dumped into the atmosphere without a major risk of exceeding 1.5°C global warming - and how soon this budget will be used up at current emission rates. It turns out that the UK's fair share of the global carbon budget will be used up in just 3.3 years. The maths are simple, but this timescale of 3.3 years is so far from what is being discussed that it is worth explaining the calculations in detail, as follows, so that readers can check for themselves.

The 2021 IPCC report [2] gives 400 billion tonnes CO2 as the global carbon budget to keep global warming to less than 1.5°C with 67% confidence. This is from the start of 2020. With a world population close to 8 billion, and using an assumption of global equity, this is 50 tonnes per person on the planet as a lifetime limit. The UK's current CO2 emissions are around 10 tonnes per person per year, according to a WWF report. [3]  So the UK's 50 tonnes per person will be used up in 5 years from January 2020, i.e. in December 2024, which is 3.3 years from now.

This should not come as a surprise to people in the UK since similar calculations were carried out by the Tyndall Centre for Climate Change Research after the 2018 IPCC report, and are readily available for each UK local authority. [4]  These typically give a fair share of the global carbon budget as running out in 7 years from 2020 at current emission rates – the period is 7 rather than 5 years since the local authority data provided by the Department for Business (BEIS) is incomplete in not including emissions that are embedded in imports. Despite being so readily available, these reports have been almost completely ignored.

Why is the need for radical change (emission cuts of double-digit percentages per year) not common knowledge? Firstly, the UK government promotes its Net Zero 2050 timescale as a satisfactory solution, [5] but it is not being sufficiently transparent that emissions from net imports are excluded, or about the implications of the commitment to global equity, or about the feasibility of the implied technological solutions. Many commentators repeat the Government's claims without challenge, but youth climate activists see through them and are speaking up about the deceits. [6] [7]  Secondly, for various reasons, many climate scientists and many non-governmental organisations are self-censoring about the size and urgency of the changes needed [8] - it is easier to campaign against the expansion of a particular airport than to explain the blunt truth that any leisure flying using fossil fuels is incompatible with a lifetime personal carbon budget of 50 tonnes CO2, since a reliable food supply and keeping warm are much higher priorities.

Yet another round of inter-governmental climate negotiations – the ‘COP26’ conference – may help, but what is really needed is for everyone to tell the truth about the climate emergency so that it is treated as an emergency, and to call out misinformation and deceits whoever makes them (however uncomfortable that is). This is advocated by Scientists for Global Responsibility (SGR) in their Science Oath for the Climate. [9]  It is clear that we cannot rely on governments to take the right decisions by themselves, however much they are urged to. It is up to citizens and scientists to be much more involved in policy-making – pointing out the tough choices that need to be made.

Ian Campbell BA BSc MD FRCS FRCR has worked as a doctor and as a medical statistics consultant. As well as medical qualifications, he has a degree in statistics and a doctorate in the use of statistical methods in cancer research - see

This blog is an edited version of a rapid response first posted on the BMJ website:



[1] IPCC (2018). Special Report on Global Warming of 1.5ºC. Summary for Policymakers.

[2] Table SPM.2 (p.29) of: IPCC (2021). Climate Change 2021: The Physical Science Basis. Working Group I contribution to the Sixth Assessment Report. Summary for Policymakers.

[3] Figure 21 (p.46) of: WWF (2020). Carbon Footprint: Exploring the UK’s Contribution to Climate Change.

[4] Tyndall Centre (2019). The Tyndall Carbon Budget Tool.

[5] See, for example: BEIS (2021). UK enshrines new target in law to slash emissions by 78% by 2035. April.
See also: Climate Change Committee (2020). Sixth Carbon Budget.

[6] Face the Climate Emergency (2021). Open Letter to World Leaders.

[8] Simms A (2020). Turning delusion into climate action - Prof Kevin Anderson, an interview. Responsible Science, no.2.

[9] SGR (2020). A science oath for the climate: text and signing.


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