A 2021 Nature Climate Change Comment by Stuart-Smith, Otto and colleagues analyzed 73 climate lawsuits and concluded that the scientific evidence submitted to courts lags far behind the state of the art in climate-change attribution science, impeding legal findings of causation. The paper's closing section identifies three research areas — attribution of climate-change impacts to individual greenhouse-gas emitters, attribution of the foreseeability of impacts from future emissions, and disentangling the legally-relevant social and physical drivers of losses — plus an explicit question of whether probability-based or intensity-based attribution metrics best serve different types of losses, and institutional recommendations on expert selection and funding. Substantial 2022–2026 progress has been made on the emitter-attribution strand, including a 2025 Nature paper arguing that the scientific case for climate liability is closed at aggregate heat-damage scale, while driver disentanglement and the comparison of probability- versus intensity-based metrics across loss types remain open. The research objective spans the source's full scientific scope — four linked components jointly serving one objective, so that attribution evidence can address the obstacles to findings of legal causation in courts — and no component is resolved at the spatial and temporal scales relevant to plaintiffs' losses, though each shows documented partial progress.

Background

Attribution science quantifies how human influence on climate changes the risk and severity of observed weather and impacts. Extreme event attribution typically asks a counterfactual question: comparing the factual world with a simulated world without anthropogenic greenhouse-gas emissions, it estimates either how much more likely an event has become (probability-based metrics, expressed as a risk ratio) or how much stronger it has become (intensity-based metrics). Impact attribution extends this chain from climate variables to harms to people and ecosystems, mediated by exposure (who and what lies in harm's way) and vulnerability (sensitivity to a given hazard). Because climate-related losses also have non-climatic drivers — land subsidence, local land-use change, differing exposure and vulnerability — courts must distinguish which drivers constitute the legally cognisable cause of a plaintiff's loss. Climate lawsuits make causal claims about the effect of defendants' greenhouse-gas emissions on plaintiffs. Establishing legal causation under tort tests such as the 'but-for' test (would the harm have occurred without the defendant's conduct?) or proportional-liability doctrines (which apportion liability according to each contributor's share of the harm) requires evidence at scales matching the plaintiff's loss. In the landmark case Lliuya v RWE AG, a Peruvian farmer sought 0.47% of flood-protection costs for a glacial-lake outburst flood hazard at Lake Palcacocha in Huaraz, Peru — the share corresponding to RWE's estimated proportion of historical industrial greenhouse-gas emissions; scientific analysis of that lake's hazard attributed its growth substantially to human-induced glacier retreat (Stuart-Smith, Roe, Li and Allen, Nature Geoscience, 2021). 'Carbon majors' are the roughly 90–180 fossil-fuel and cement producers whose historical emissions dominate the industrial total, inventoried by researcher Richard Heede. Related concepts: 'foreseeability' (whether future impacts of ongoing emissions were reasonably predictable, which matters for standing and remedies), 'loss and damage' (the policy stream of the United Nations Framework Convention on Climate Change (UNFCCC) for climate harms), the 'social cost of carbon' (the discounted damage caused by one tonne of emitted CO2), and 'scope 1 and 3 emissions' (a company's direct emissions, and emissions from use of its products, respectively). Against this background, Stuart-Smith et al. (2021) evaluated 73 lawsuits across 14 jurisdictions, found the evidence submitted lagged the state of the art, and argued that better exploitation of attribution science could clear obstacles to causation findings. Their closing section identifies three research areas — (1) attribution of climate-change impacts to individual emitters of greenhouse gases (which they judged possible with existing methods), (2) research on the foreseeability of climate-change impacts resulting from future emissions, and (3) research disentangling the legally-relevant social and physical drivers of climate risks and impacts, which they called the most methodologically challenging — plus the question of whether probability- or intensity-based attribution metrics best assess the contribution of climate change to different types of losses, and closing institutional recommendations on legal-scientific dialogue, independent expert selection, and funding for the science.

Problem Statement

The research objective is an umbrella question with linked components, posed in the closing section of Stuart-Smith et al. (2021, Nature Climate Change 11, 651-655, doi:10.1038/s41558-021-01086-7): what scientific research would close the evidentiary gap that keeps attribution science from addressing the obstacles to findings of causation in climate litigation? The linked components, in the paper's own formulation, are: (1) attribution of climate-change impacts to individual emitters of greenhouse gases, operationalised through counterfactual analyses that quantify an individual emitter's marginal contribution to extreme events, slow-onset changes, and projected future impacts at the spatial and temporal scales relevant to plaintiffs' losses (the paper judges this possible with existing attribution methods, and notes courts have incorrectly declared it infeasible); (2) research on the foreseeability of climate-change impacts resulting from future emissions, to support standing and remedy claims; (3) research disentangling the legally-relevant social and physical drivers of climate risks and impacts — quantifying how much of a loss is attributable to climatic drivers versus non-climatic ones such as land subsidence, land-use change, and differential exposure and vulnerability — so courts can identify the legally cognisable cause(s) of harm; and (4) determining whether probability-based or intensity-based attribution metrics better assess the contribution of climate change to different types of losses, given that intensity evidence may align more closely with 'but-for' causation logic. The paper accompanies these with institutional recommendations (legal-scientific dialogue, selection of independent experts, and funding for the science) that condition whether such evidence reaches and is used by courts; they are not themselves scientific subquestions of the agenda, which concerns the evidence that attribution science can supply. The question asks what research, at the spatial and temporal scales relevant to plaintiffs' losses, each of the four jointly posed components requires, and how the resulting evidence would address the corresponding obstacle to a finding of legal causation in courts.

References

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