Non-state and subnational climate actors have become central to global climate change governance. Quantitatively assessing climate mitigation undertaken by these entities is critical to understand the credibility of this trend. In this Perspective, we make recommendations regarding five main areas of research and methodological development related to evaluating non-state and subnational climate actions: defining clear boundaries and terminology; use of common methodologies to aggregate and assess non-state and subnational contributions; systematically dealing with issues of overlap; estimating the likelihood of implementation; and addressing data gaps.

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We thank participants at an April 2017 workshop held at University College London in London, UK, as well as a November 2017 workshop in Bonn, Germany, who provided feedback on early thinking and drafts of this paper. This work was funded by ClimateWorks Foundation grant no. 17-1101.

Author information


  1. Yale School of Forestry and Environmental Studies, Yale University, New Haven, CT, USA

    • Angel Hsu
  2. Yale-NUS College, Singapore, Singapore

    • Angel Hsu
  3. Wageningen University & Research, Wageningen, the Netherlands

    • Niklas Höhne
  4. NewClimate Institute, Cologne, Germany

    • Niklas Höhne
    • , Takeshi Kuramochi
    •  & Katharina Lütkehermöller
  5. Copernicus Institute of Sustainable Development, Utrecht University, Utrecht, the Netherlands

    • Takeshi Kuramochi
  6. PBL Netherlands Environmental Assessment Agency, The Hague, the Netherlands

    • Mark Roelfsema
  7. Data-Driven Yale, Yale School of Forestry and Environmental Studies, New Haven, CT, USA

    • Amy Weinfurter
    •  & Yihao Xie
  8. Deutsches Institut für Entwicklungspolitik, Bonn, Germany

    • Sander Chan
  9. New Climate Economy, Washington, DC, USA

    • Jan Corfee-Morlot
  10. UN Environment, Nairobi, Kenya

    • Philip Drost
  11. CDP, London, UK

    • Pedro Faria
    •  & Shirin Reuvers
  12. AG Climate and Energy Ltd, Reading, UK

    • Ann Gardiner
  13. University of California, Santa Cruz, Santa Cruz, CA, USA

    • David J. Gordon
  14. Blavatnik School of Government, University of Oxford, Oxford, UK

    • Thomas Hale
  15. School of Public Policy, University of Maryland, College Park, MD, USA

    • Nathan E Hultman
  16. Drawdown Switzerland, Nyon, Switzerland

    • John Moorhead
  17. Grantham Research Institute on Climate Change and the Environment, London School of Economics and Political Science, London, UK

    • Joana Setzer
  18. World Resources Institute, Washington, DC, USA

    • Neelam Singh
  19. World Wildlife Fund, Washington, DC, USA

    • Christopher Weber
  20. Institute for Environmental Studies, Vrije Universiteit Amsterdam, Amsterdam, the Netherlands

    • Oscar Widerberg


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A.H., N.H., T.K., M.R., A.W., Y.X. and K.L. conceived the concept and led the analysis and writing. All other authors substantially contributed suggestions, ideas and writing.

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The authors declare no competing interests.

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Correspondence to Angel Hsu.

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