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The last chance COP? Some more carbon budget maths!


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Mar 22, 2024
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With world leaders and thousands of delegates and observers meeting in Glasgow for COP26, there is much talk of this being the last chance to save 1.5°C. It wouldn’t be the first time a COP has been described as the last chance we have, but in the case of COP26 and 1.5°C, it is a fair assessment of the situation. It all rests on the available carbon budget which I discussed in a recent post.

In the August 2021 6th Assessment Report from IPCC WGI, the carbon budget analysis for 1.5°C was published, as shown in the table below.

Estimates of historical CO2 emissions and remaining carbon budgets (Source: IPCC)


In its recent NZE 2050 scenario, the IEA used the mid range figure of 500 Gt from 1.1.2020 as the carbon budget for the analysis, although we should recognise that for a greater degree of certainty of not exceeding 1.5°C a lower number is more desirable. But we are two years on from the baseline of 1.1.2020 with cumulative carbon dioxide emissions since that time of some 80 Gt, so from 1.1.2022 which is now just a few weeks away, the carbon budget for 1.5°C is closer to 400 Gt. This sits against global annual carbon dioxide emissions of over 40 Gt, comprising 33 Gt from fossil fuel use, 3 Gt from the calcination of limestone for cement manufacture and 6 Gt as a result of land use change practices, which includes ongoing deforestation.

So with at most 400 Gt of remaining budget and it diminishing by 1 Gt every 9 days (so 1.5 Gt while COP26 is on), the challenge facing the conference is huge. 2021 (originally 2020 in the Paris Agreement but delayed due to COVID-19) is the year in which countries are asked through the Paris Agreement to reassess their initial Nationally Determined Contributions and to increase ambition in light of the prevailing science. Indeed, that process is well underway and a quick look at the UNFCCC NDC Registry will show many new submissions, with more appearing each day.

A quick analysis of the NDCs reveals that in the 2020s global society is likely to consume much of the remaining carbon budget for 1.5°C, which implies that the temperature goal is breached soon after the decade is over (although it may be some years after that the IPCC and WMO confirm this). Just ten medium to large emitting countries account for some 200 Gt in the 2020s, based on the emissions pathways they have announced through their existing or revised NDCs and assuming that these are delivered. That list includes China, the USA, India, the EU, Australia, the UK, Canada, Korea, Japan and Russia. These ten make up about two thirds of current global energy system emissions. China is the largest, with emissions currently around 10 Gt per year. Their revised NDC was submitted last week and brings forward their peaking of emissions to ‘before 2030’. I have assumed that their emissions plateau now, then being falling in 2027 and drop to 9 Gt per year by 2030.

Most of the countries outside my ten, albeit not all, either have modest current emissions and are therefore likely to see short term increases as development continues, or at best will plateau at their current levels. This includes Brazil, Indonesia and all of the African (1.3 Gt energy emissions in 2019) and Middle East (2.1 Gt energy emissions in 2019) countries. The 10+ Gt per year for nine years that these countries represent is around 100+ Gt, so that takes the total to 300+ Gt. Add to this international aviation and marine bunkers over a decade and another 15-20 Gt of the budget is consumed. The total by 2030 is therefore becoming perilously close to 400 Gt and will certainly exceed the tighter 67% and 83% numbers in the table above. At best the NDCs might see carbon dioxide emissions at around 30 Gt per year by 2030, with a remaining budget of 60-80 Gt going into the 2030s and beyond.

While there is a very strong focus at COP26 on net-zero emissions in 2050, the real challenge for 1.5°C is within this decade. The next round of NDCs won’t be submitted until 2025 if the Paris schedule is maintained, by which time another 160-200 Gt of carbon dioxide could have been emitted based on a global plateau at current levels. This really will be too late to make changes for 1.5°C, so it has to be in 2021 with COP26 acting as the catalyst for change.
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