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. 2024 Nov 14;15(1):9562.
doi: 10.1038/s41467-024-53645-z.

Systematic assessment of the achieved emission reductions of carbon crediting projects

Benedict S Probst  1   2   3 , Malte Toetzke  4   5 , Andreas Kontoleon  6 , Laura Díaz Anadón  6   7 , Jan C Minx  8   9 , Barbara K Haya  10 , Lambert Schneider  11 , Philipp A Trotter  12   13 , Thales A P West  6   14 , Annelise Gill-Wiehl  15 , Volker H Hoffmann  16
Affiliations

Systematic assessment of the achieved emission reductions of carbon crediting projects

Benedict S Probst et al. Nat Commun. .

Abstract

Carbon markets play an important role in firms' and governments' climate strategies. Carbon crediting mechanisms allow project developers to earn carbon credits through mitigation projects. Several studies have raised concerns about environmental integrity, though a systematic evaluation is missing. We synthesized studies relying on experimental or rigorous observational methods, covering 14 studies on 2346 carbon mitigation projects and 51 studies investigating similar field interventions implemented without issuing carbon credits. The analysis covers one-fifth of the credit volume issued to date, almost 1 billion tons of CO2e. We estimate that less than 16% of the carbon credits issued to the investigated projects constitute real emission reductions, with 11% for cookstoves, 16% for SF6 destruction, 25% for avoided deforestation, 68% for HFC-23 abatement, and no statistically significant emission reductions from wind power and improved forest management projects. Carbon crediting mechanisms need to be reformed fundamentally to meaningfully contribute to climate change mitigation.

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Conflict of interest statement

Competing interests The authors declare the following competing interests: L.S. is a member of the Executive Board of the Clean Development Mechanism. The other authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Overview of total issuance and relative share of sectors across all major crediting mechanisms.
a Total issuance in gigatons CO2 across the Kyoto Protocol’s two project-based mechanisms (Clean Development Mechanism and Joint Implementation) and the four major independent mechanisms covered by the Berkeley Carbon Trading Project Database (American Carbon Registry (ACR), Climate Action Reserve (CAR), Gold Standard (GS) and Verified Carbon Standard (VCS)). b Total issuance in % across different sectors under Kyoto and independent mechanisms. Data is based on Clean Development Mechanism’s (CDM) database for PAs and PoAs, the United Nations Environment Programme (UNEP) RISOE database for JI and the Berkeley Carbon Trading Project Database v9. Other crediting mechanisms are excluded as they only constitute a minor share of issued credits. The sector ‘other’ contains carbon capture and storage, agriculture and transportation.
Fig. 2
Fig. 2. Overview of studies in the systematic assessment.
a/b Distribution of studies across project types, (c/d) across regions and (e/f) methodology types. Note: k refers to the number in thousands, and m refers to the number in millions. See Supplementary Tables 4 and 5 for a full list of studies. Note: IFM refers to improved forest management. If the same project was evaluated by multiple studies, we count each as a separate project evaluation as the time frame, methodology and other relevant factors might differ. The total project number includes studies that could not be integrated into our quantitative framework (e.g. ref. ) but are still discussed in the relevant sections.
Fig. 3
Fig. 3. Sources of under/over-crediting analysed by carbon crediting studies covered in our assessment.
The name of the authors shows the study, which analysed the specific source of over/under-crediting, otherwise, the box indicates ‘No’. The figure excludes several studies that analyse offset quality, namely Calel et al. Badgley et al. Holm et al. and Bomfim et al., because they could not be integrated into our quantitative assessment framework, but the findings are reviewed in the discussion section. Reasons for exclusion for each of these studies can be found in Supplementary Table 7. Only the first author’s name is shown due to space constraints. Note that the figure does not cover the field interventions as these did not issue carbon credits and, therefore, could not be integrated into our quantitative framework. IFM refers to Improved Forest Management.
Fig. 4
Fig. 4. Estimated offset achievement ratio of carbon crediting projects.
a Estimated offset achievement ratio for project types for which we found relevant studies. b Project-level estimates extracted from relevant studies for individual projects. Only the first authors are mentioned in the study section for visualisation purposes. Two studies excluded that only showed upper-bound estimates refs. , and two studies that could not be integrated into the framework,; see Supplementary Table 7 for detailed exclusion reasons. Estimated average offset achievement ratios in (a) are the weighted average of projects’ OAR based on the issued credits (i.e. projects that issued more credits are weighted more). Each dot in (b) represents one project-level OAR, with the colours corresponding to the underlying studies. Confidence intervals in (a) are the weighted variance (by credit issuance) based on the individual estimates in (b), whereas the centre of the error bar represents the weighted average for each project type. The exact issued credits and the OAR for each project can be found in the supplementary data. ACR refers to the American Carbon Registry, CAR to Climate Action Reserve, CDM to Clean Development Mechanism, VCS to Voluntary Carbon Standard, GS to Gold Standard, JI to Joint Implementation and IFM to Improved Forest Management.
Fig. 5
Fig. 5. Estimated offset achievement.
a Credits covered in our analysis relative to the total volume of issued credits based on sources from Fig. 1a. b Estimated achieved vs non-achieved emission reductions across covered projects based on percentage estimates from Fig. 4a. c Disaggregated shares of estimated achieved and non-achieved emission reductions across covered projects. IFM refers to improved forest management.
Fig. 6
Fig. 6. Estimated offset achievement ratio of avoided deforestation projects analysed in two studies.
a Offset achievement ratio across studies. b Average 5-year issuance in million tons CO2. Based on West et al., and Guizar-Coutiño et al.. Credit data is based on the VCS registry and contains all credits that have been issued. Please note that for the main estimates in Fig. 4, we use the estimates from the full sample of projects, which is an OAR of 24.7% (compared to an OAR of 14.5% on average for this subset of 26 projects). Average 5-year issuance is based on the total issuance from project start year to 2024 (calculated by dividing total issuance by total years since inception, multiplied by five).
See this image and copyright information in PMC

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