This is the first in our series on removal-based carbon credits that will run throughout February and March.

Calyx Global has released our first credit rating from a concrete project under VM0043. This methodology accounts for over 99% of the credits currently on the market. Such projects have significant potential. After all, the world uses more than 30 billion tons of concrete annually for buildings, bridges, infrastructure and other applications. Global cement manufacturing, which produces the primary ingredient in concrete, resulted in 1.5 billion tons of CO2 last year, generating 4% of the world’s CO2 emissions. 

These projects deliver emission reductions, not removals 

Because VM0043 features the injection of CO2 into the concrete mix, some have touted its potential to deliver removals. However, our research shows that is not the case. Cement, the binding agent in concrete, begins to take up CO2 as soon as it is poured in a process called ‘carbonation.’ The injection of CO2 simply speeds up a process of CO2 sequestration that would occur naturally, in the absence of the injection. 

This technology can reduce emissions by around 5% 

These projects deliver emission reductions because they allow producers to use less cement (a fossil-fuel-intensive input). Other efforts in the sector led to a 2.8% reduction in emissions last year[1]. If adopted throughout the world, this methodology could almost double the rate of emission reduction in this difficult-to-abate sector.

While CO2 injection can actually result in lower costs, and several government initiatives encourage the adoption of low-CO2 concrete, the technology is still nascent and barriers to adoption persist. Until the approach is more mature, carbon finance can play an important role in promoting the adoption of this technology. 

However, the methodology results in substantial over-crediting 

The natural carbonation of cement negates between 20 and 50% of the emissions associated with concrete production over the lifetime of the concrete[2][3][4][5]. These natural ‘removals’ of CO2 from the atmosphere offset emissions from the fossil fuels used to produce cement. As a result, the net emissions are about 40% lower than they appear to be if only fossil fuel emissions are counted. Although natural carbonation is included in global emissions accounting such as the annual update by the Global Carbon Project, VM0043 does not account for it. As a result, baseline emissions are substantially overestimated. 

Rightsizing could provide a ‘fix’. Because this project type can justify its additionality due to the low uptake of the technology at present and it has no risk of non-permanence, over-crediting can be addressed by recalculating the number of credits generated. We call this rightsizing and believe this can be a useful approach when methodologies allow over-crediting. 

Conclusion

Tackling concrete is important. It is one of the hardest-to-abate sectors. Most of the emissions come from processing cement. Managing emissions from cement will require scaling up carbon capture, which is currently cost-prohibitive in most instances. There are a few options to avoid the use of cement, such as shifting to timber as a substitute for building material, but also many applications where there are currently no alternatives. Total cement production is expected to grow rapidly in the coming years. Therefore, tackling this sector is critical and this project type – if it measures actual emission reductions well – can contribute to reducing global emissions.

Follow us on LinkedIn to keep up with our ongoing series on carbon removals. Next up: “The state of GHG quality of removal-based carbon projects.” 

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[1] Friedlingstein et al. (2024). Global Carbon Budget 2024. Accessible at: https://essd.copernicus.org/preprints/essd-2024-519/

[2] Guo et al. (2021). Global CO2 uptake by cement from 1930 to 2019. Accessible at: https://essd.copernicus.org/articles/13/1791/2021/essd-13-1791-2021.html

[3] Xi et al. (2016). Substantial global carbon uptake by cement carbonation. Accessible at: https://www.nature.com/articles/ngeo2840

[4] Fitzpatrick et al. (2015). Sequestration of Carbon Dioxide by Concrete Infrastructure: a Preliminary Investigation in Ireland. Accessible at: https://www.ceeol.com/search/article-detail?id=482434

[5] Andersson et al. (2013). Calculation CO2 Uptake for Existing Concrete Structures during and after Service Life. Accessible at: https://pubs.acs.org/doi/abs/10.1021/es401775w#