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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.
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.
- The IPCC AR6 WG1 report of August 2021 gave 400 billion tonnes (400Gt) as the maximum amount of CO2 that can be emittted globally without a major risk of devastating consequences [1]. To be precise, this is 400 billion tonnes from 1 Jan 2020 to give 67% confidence of keeping global warming to 1.5 deg C. This is an update on the IPCC SR15 report of October 2018 [2] which gave 420 billion tonnes from 1 Jan 2018 for the same figure.
- With a world population reaching 8 billion in the next few years, this 400 billion tonnes is 50 tonnes of CO2 per person when shared equally. This is a total lifetime limit.
- The UK CO2 emissions are around 10 tonnes per person per year [3], and so its carbon budget will run out in 5 years i.e. at the end of 2024.
- To stay within this budget, UK citizens now need to make radical reductions in emissions (as explained by the IPCC). Some simple maths tells us that reducing the UK average by 20% per year as an exponential decline will achieve this - see charts. A reduction of 20% year-on-year is about the same as halving every 3 years.
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.References
| [1] | IPCC (Aug 2021) AR6 Climate Change 2021: The Physical Science Basis https://www.ipcc.ch/report/ar6/wg1/ |
| [2] | IPCC SR15 Report p108 (p16 of chapter 2) https://www.ipcc.ch/site/assets/uploads/sites/2/2019/05/SR15_Chapter2_Low_Res.pdf |
| [3] | https://www.carbonindependent.org/23.html |
| [4] | The Tyndall Carbon Budget Tool https://carbonbudget.manchester.ac.uk/reports/ |
| [5] | https://www.carbonindependent.org/files/LCR_Tyndall_Centre_carbon_budget_report.pdf |
First published: Dec 2019
Last updated: 17 Jul 2023