Climatic Change

, Volume 155, Issue 4, pp 545–561 | Cite as

Not all carbon dioxide emission scenarios are equally likely: a subjective expert assessment

  • Emily HoEmail author
  • David V. Budescu
  • Valentina Bosetti
  • Detlef P. van Vuuren
  • Klaus Keller


Climate researchers use carbon dioxide emission scenarios to explore alternative climate futures and potential impacts, as well as implications of mitigation and adaptation policies. Often, these scenarios are published without formal probabilistic interpretations, given the deep uncertainty related to future development. However, users often seek such information, a likely range or relative probabilities. Without further specifications, users sometimes pick a small subset of emission scenarios and/or assume that all scenarios are equally likely. Here, we present probabilistic judgments of experts assessing the distribution of 2100 emissions under a business-as-usual and a policy scenario. We obtain the judgments through a method that relies only on pairwise comparisons of various ranges of emissions. There is wide variability between individual experts, but they clearly do not assign equal probabilities for the total range of future emissions. We contrast these judgments with the emission projection ranges derived from the shared socio-economic pathways (SSPs) and a recent multi-model comparison producing probabilistic emission scenarios. Differences on long-term emission probabilities between expert estimates and model-based calculations may result from various factors including model restrictions, a coverage of a wider set of factors by experts, but also group think and inability to appreciate long-term processes.


Funding information

David Budescu’s work was supported in part by Grant 2015206 from the Binational Science Foundation, USA-Israel. Valentina Bosetti acknowledges funding from the European Research Council under the European Community’s Programme “Ideas” - Call identifier: ERC-2013-StG / ERC grant agreement n° 336703– project RISICO “RISk and uncertainty in developing and Implementing Climate change pOlicies”. Klaus Keller’s work was supported by the Penn State Center for Climate Risk Management. We gratefully acknowledge Mark Himmelstein for coding assistance for the first study. Any conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funding agencies.

Supplementary material

10584_2019_2500_MOESM1_ESM.docx (1.3 mb)
ESM 1 (DOCX 1335 kb)


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Fordham UniversityThe BronxUSA
  2. 2.RFF-CMCC European Institute on Economics and the EnvironmentBocconi UniversityMilanItaly
  3. 3.PBL Netherlands Environmental Assessment AgencyUtrecht UniversityUtrechtNetherlands
  4. 4.Pennsylvania State UniversityState CollegeUSA

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