The maths of staying within the CO2 budget: Halve UK emissions every 3 years

The IPCC has published the limit to further burning of fossil fuel that would give confidence of keeping global warming to 1.5°C.

This remaining global CO2 budget is 400 billion tonnes CO2 from Jan 2020.

This is equal to a lifetime budget from Jan 2020 of 50 tonnes CO2 per person on the planet.

For an average UK citizen, this CO2 budgt will run out in 5 years.

One option to make the budget last longer is to halve UK emissions every 3 years.

Nothing like this is happening or even being widely discussed.

Three simple options for staying within a budget of 50 tonnes CO2

Option 1: No decline - the budget lasts 5 years

Option 2: Steady (linear) decline - the budget lasts 9 years

Option 3: 20% annual (exponential) decline - the budget lasts for decades

Other sources

The Tyndall Climate Centre in Manchester has published an online tool for generating a carbon budget report for each local authority in the UK [4]. It can also generate aggregate budgets for groups of local authorities, such as Liverpool City Region [5].

Theory versus reality

Changes of the size discussed here have clearly not happened, and outside academic circles, they have not been widely discussed. It seems that most people have no understanding that changes such as these are necessary, if they care about a habitable planet - it's not that they have considered such changes and decided agiant them.


[1]IPCC (Aug 2021) AR6 Climate Change 2021: The Physical Science Basis
[2] IPCC SR15 Report p108 (p16 of chapter 2)
[4]The Tyndall Carbon Budget Tool

First published: Dec 2019
Last updated: 17 Jul 2023