Abstract
Standards of proof for attributing real world events/damage to global warming should be the same as in clinical or environmental lawsuits, argue Lloyd et al. The central question that we raise is effective communication. How can climate scientists best and effectively communicate their findings to crucial non-expert audiences, including public policy makers and civil society? To address this question, we look at the mismatch between what courts require and what climate scientists are setting as a bar of proof. Our first point is that scientists typically demand too much of themselves in terms of evidence, in comparison with the level of evidence required in a legal, regulatory, or public policy context. Our second point is to recommend that the Intergovernmental Panel on Climate Change recommend more prominently the use of the category “more likely than not” as a level of proof in their reports, as this corresponds to the standard of proof most frequently required in civil court rooms. This has also implications for public policy and the public communication of climate evidence.
Highlights
We suggest that the Intergovernmental Panel on Climate Change (IPCC) should apply routinely the category of “more likely than not” in all of its reporting contexts, recognizing its legal and policy relevance
The category was minimized after the Fourth Assessment Report, appearing only as a footnoted possibility in the IPCC uncertainty guidance document (Table 1); we argue that it should be recommended again as an established and
This can be done by the IPCC instituting a new guidance, in which “more likely than not” is highlighted as a relevant assessment level for legal contexts to be used throughout the assessment reports wherever authors find it appropriate
Summary
Consider our situation with the coronavirus. We often have to make a variety of policy, practical, and legal decisions based on incomplete information, which also depend on judgements about whether the evidence is good enough. What level of evidence do we need, in the
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