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# Attributing agnostically detected large reductions in road CO2 emissions to policy mixes

## Abstract

Policymakers combine many different policy tools to achieve emission reductions. However, there remains substantial uncertainty around which mixes of policies are effective. This uncertainty stems from the predominant focus of ex post policy evaluation on isolating effects of single, known policies. Here we introduce an approach to identify effective policy interventions in the EU road transport sector by detecting treatment effects as structural breaks in CO2 emissions that can potentially occur in any country at any point in time from any number of a priori unknown policies. This search for ‘causes of effects’ within a statistical framework allows us to draw systematic inference on the effectiveness of policy mixes. We detect ten successful policy interventions that reduced emissions between 8% and 26%. The most successful policy mixes combine carbon or fuel taxes with green vehicle incentives and highlight that emissions reductions on a magnitude that matches the EU zero emission targets are possible.

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$32.00 All prices are NET prices. ## Data availability All publicly available data analysed in this study are available from the corresponding author upon request and are also available from online repository Zenodo (https://doi.org/10.5281/zenodo.6768563). ## Code availability The code required to replicate our study is available from the corresponding author upon request and is also available from online repository Zenodo (https://doi.org/10.5281/zenodo.6768563). ## References 1. Net Zero by 2050—A Roadmap for the Global Energy Sector (IEA, 2021). 2. Axsen, J., Plötz, P. & Wolinetz, M. Crafting strong, integrated policy mixes for deep CO2 mitigation in road transport. Nat. Clim.Change 10, 809–818 (2020). 3. Planning for Net Zero: Assessing the Draft National Energy and Climate Plans (Ecologic & Climact, 2019). 4. Trends and Projections in Europe 2021 (European Environment Agency, 2021). 5. Graf, A., Graichen, J., Matthes, F. C., Gores, S. & Fallasch, F. 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## Acknowledgements

We thank O. Edenhofer, A.B. Martinez, R. Tol and the participants at the EC2 Conference 2021, the Federal Reserve Virtual Seminar on Climate Economics and the Climate Econometrics Seminar for valuable feedback and suggestions. F.P. and M.S. gratefully acknowledge funding from the Clarendon Fund and the Robertson Foundation. F.P. is also grateful to funding from Social Sciences and Humanities Research Council of Canada (SSHRC). The views expressed here are those of the authors and not necessarily those of the Ministry of Finance or the Austrian government.

## Author information

Authors

### Contributions

F.P., L.N., M.S. and N.K. designed the analysis. F.P. and M.S. wrote the core programme code. L.N. collected the data. L.N. and N.K. conducted most of the analyses. All authors interpreted results and designed figures. N.R. and N.K. wrote the manuscript with contributions from all authors.

### Corresponding author

Correspondence to Nicolas Koch.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

## Peer review

### Peer review information

Nature Energy thanks Patrick Bayer, Edgar Hertwich and Md. Saniul Alam for their contribution to the peer review of this work.

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## Supplementary information

### Supplementary Information

Supplementary Sections A–C and Tables 1–12.

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Koch, N., Naumann, L., Pretis, F. et al. Attributing agnostically detected large reductions in road CO2 emissions to policy mixes. Nat Energy 7, 844–853 (2022). https://doi.org/10.1038/s41560-022-01095-6

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• DOI: https://doi.org/10.1038/s41560-022-01095-6