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Establishing causation in climate litigation: admissibility and reliability


Climate litigation has attracted renewed interest as a governance tool. A key challenge in climate litigation is to assess the factual basis of causation. Extreme weather attribution, specifically the Fraction of Attributable Risk (FAR), has been proposed as a way to tackle this challenge. What remains unclear is how attribution science interacts with the legal admissibility of evidence based on climate models. While evidence has to be legally admissible in order to be considered in a trial, it has to be reliable in order for the court to arrive at a legally correct conclusion. Since parties to the trial have incentives to produce evidence favorable to their case, admissibility requirements and the reliability of the evidence brought forward are linked. We provide a specific proposal for how to accommodate FAR estimates in admissibility standards by modifying an existing set of admissibility criteria, the Daubert criteria. We argue that two of the five Daubert criteria are unsuitable for dealing with such evidence and that replacing those criteria with ones directly addressing the reliability of FAR estimates is adequate. Lastly, we highlight the dependence of courts on both the existence and accessibility of a framework to determine the reliability of FAR estimates in executing such criteria.

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Fig. 1


  1. Solar Geoengineering is a novel, untested, but potentially effective form of intervention in the global climate system with the purpose of counteracting global warming. Deployment, however, will entail the risk of undesirable side effects (Schäfer et al. 2015, Ocean Studies Board and National Research Council (2015), Niemeier and Tilmes 2017).

  2. By the “attribution community,” we mean the scientists regularly publishing work related to the attribution of extreme events. When we state that this community “does” something, we contend that this “doing” reflects the big picture of the relevant literature.

  3. For example, in common law States, the standard of preponderance of the evidence, usually taken to mean “more likely than not”, is most common in civil law.

  4. FAR has its origin in epidemiology. However, there are clear limitations in the comparability of its application in attribution science and in epidemiology (Shepherd 2016).

  5. This a simplification of the legal reality in that the two steps are not formally separated in all jurisdictions. However, for the purposes of this paper, the simplification is innocuous (see Online Resource).

  6. We use the terms reliable and reliability in a strictly epistemological sense. In legal contexts, “evidentiary reliability” of evidence is sometimes used as a criterion for admissibility. In social sciences other than law, “reliability” is usually employed as a prerequisite of “validity” and has the meaning of consistency or repeatability (Carmines and Zeller 1979). In order to avoid terminological confusion, we emphasize that we exclusively refer to the epistemological definition provided below. For a more detailed discussion of these terms and definitions, see Haack (2008).

  7. For example, arbitrary requirements like “the modeling choices must have appeared in the IPCC reports” may well decrease the reliability of the FAR estimates produced.

  8. Event attribution exclusively based on observations is not capable of discerning the purely anthropogenic influence on extreme events.

  9. Note that the US Supreme Court explicitly refers to Popper in its judgment in which it developed the Daubert criteria, and it explicitly equates testability and falsifiability.

  10. While a “magnitude” approach is not suitable for answering questions of probabilistic causation, it may well be the right approach for answering other questions pertaining to other stages of a trial, e.g., damage determination.


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The authors gratefully acknowledge funding by the German Research Foundation DFG under grant numbers CA120/19-2 (MC, JL), GO1604/3-2 (TG, TP), PR1323/2-2 (AP, HM), and SCHM2158/4-2 (HS, UN).

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TP developed the basic idea and concept underlying the study. All of the authors have contributed to the development of idea and concept of this paper and to the writing. TP, TG, and AP have drafted large parts of the manuscript. TP coordinated the writing process and calculated the FAR estimates. UN has performed the climate model simulations and contributed to their analysis.

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Correspondence to Tobias Pfrommer.

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Pfrommer, T., Goeschl, T., Proelss, A. et al. Establishing causation in climate litigation: admissibility and reliability. Climatic Change 152, 67–84 (2019).

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