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  • Letter
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Robust eligibility criteria essential for new global scheme to offset aviation emissions


Aviation may have contributed as much as 4.9% to global radiative forcing in 2005 and its carbon dioxide emissions could grow by up to 360% between 2000 and 20501. In 2016, the International Civil Aviation Organization adopted a global scheme requiring airline operators to offset increases in carbon dioxide emissions from international flights above 2020 levels2,3. Here we show that the scheme will only compensate for the emissions increase if robust criteria for the eligibility of offset credits are adopted. Offset supply from already implemented greenhouse gas abatement projects registered under the Clean Development Mechanism alone could exceed demand from International Civil Aviation Organization’s scheme. Most of these projects continue abatement even if they cannot sell offset credits. If the scheme allows airline operators the unlimited use of offset credits from already implemented projects, it will result in no notable emissions reductions beyond those that would occur anyway and neither offer incentives for new investments nor reward previous investments in offset projects. We recommend limiting the eligibility to new projects or projects that are at risk of discontinuing greenhouse gas abatement without further support. The findings are critical for negotiations under both the International Civil Aviation Organization and the Paris Agreement.

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Fig. 1: CER supply potential for the period 2013–2020 by major project types and vulnerability to discontinuing GHG abatement.
Fig. 2: Marginal costs of supplying CERs for the period 2013–2020.

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Data availability

Parts of the datasets generated during or analysed for this Letter are available upon request. The data can only be made available in aggregated form and some parts of the data cannot be provided due to the confidential nature of the survey responses and plant-specific data used in this letter.


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The German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) provided research funds for analysing the status quo of CDM projects (project number FKZ UM13 41 173). The German Emissions Trading Authority at the German Environment Agency (DEHSt/UBA) provided research funds for analysing the vulnerability of CDM projects for discontinuation of mitigation activities, for the analysis of the CDM supply potential up to 2020 and for analysing the marginal cost of CER supply and implications of demand sources (project number FKZ 3715 42 510 0). The Federal Ministry of Agriculture, Forestry, Environment and Water Management of Austria and the Office of Environment of Liechtenstein provided research funds for the analysis on using the CDM for nationally determined contributions and international aviation. The funders provided terms of reference for these underlying research projects but had no role in performing the research or in the decision to submit this letter. The research team bears sole responsibility for the content.

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Authors and Affiliations



C.W. and T.D. conducted the survey and evaluated the survey data on the status of implementation and operation of CDM projects. T.D. led the research on the vulnerability of projects with support from C.W. and L.S. The assessment of the CER supply potential was led by L.S. and S.L.H.T with support from T.D. and C.W. The development of the marginal costs data was led by H.F. with support from all authors. L.S. led the writing of the article with support from all authors.

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Correspondence to Lambert Schneider.

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Competing interests

L.S. is an alternate member of the Executive Board of the CDM. All other authors have no competing interests.

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Journal peer review information Nature Climate Change thanks John Broderick, Susanne Becken and other anonymous reviewer(s) for their contribution to the peer review of this work.

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Warnecke, C., Schneider, L., Day, T. et al. Robust eligibility criteria essential for new global scheme to offset aviation emissions. Nat. Clim. Chang. 9, 218–221 (2019).

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