1. INTRODUCTION
Attribution science is a relatively new field of research which seeks to establish a link between drivers of climate change - in particular rising greenhouse gas (GHG) emissions - and observed changes in climatic variables.
Plaintiffs are increasingly relying on the findings of attribution science in climate litigation against companies in order to compel them to reduce the level of GHG emissions and to establish liability for damages caused by climate change-related weather events.
In this report, we briefly explain what attribution science is and the role it may play in climate litigation, particularly in relation to the plaintiff's burden to prove (legal) causation in civil liability actions.
2. WHAT IS ATTRIBUTION SCIENCE?
In other words, attribution science is a statistical exercise that examines the impact of anthropogenic (i.e. human-induced) climate change factors on human or natural systems. For example, the IPCC has found that human-induced climate change is likely the main driver of the increased frequency and intensity of heavy precipitation since 1950 (IPCC Sixth Assessment Report (2021), Summary for Policymakers, A.3.2).
Since its inception in the early 2000s, attribution science has been applied in different types of studies, including:
3. USE OF ATTRIBUTION SCIENCE IN COURT PROCEEDINGS AGAINST COMPANIES
3.1 Examples
Plaintiffs are relying on attribution science in order to hold companies accountable for the alleged consequences of their historical GHG emissions (liability actions) and to compel companies to reduce their emissions going forward (climate change mitigation actions; for an overview, see Climate Dispute Risk for (Swiss) Companies).
In Milieudefensie et al v
- "the goals of the Paris Agreement [as derived from the IPCC reports] represent the best available scientific findings in climate science, which is supported by widespread international consensus";
- "the court assumes that it is generally accepted that global warming must be kept well below 2şC in 2100, and that a temperature rise of under 1.5şC should be strived for";
- "there is a widely endorsed consensus that in order to limit global warming to 1.5°C, reduction pathways that reduce CO2 emissions by net 45% in 2030, relative to 2010 levels, and by net 100% in 2050, should be chosen".
In a case currently pending before the German courts, Luciano Lliuya v.
Another example relates to proceedings in
In
3.2 Limitations of attribution science in legal proceedings
As highlighted by the CHRP in
In order to establish legal causation, plaintiffs must demonstrate that an act of the defendant caused the loss for which they are claiming damages or another remedy. In many jurisdictions, this is primarily done by applying:
- a counterfactual or 'but for' test and/or
- tests involving normative considerations (such as foreseeability or 'adequacy').
The standard of proof required to establish legal causation may vary considerably between jurisdictions, with some adopting a 'balance of probabilities' standard, while others require a 'near certainty' standard.
Attribution science seeks to establish risks and probabilities and to determine whether a specific element (such as CO2 emissions) contributed or is likely to contribute to an event.
Even if the causal link between greenhouse gas emissions and climate change (i.e. climate change attribution) is increasingly accepted as scientific fact, the same cannot be said for other areas of attribution science.
Plaintiffs must therefore still persuade the court:
- that (and to what extent) the defendants' emissions contributed to climate change, and
- that (and to what extent) climate change caused a specific event (e.g. a hurricane, flood, etc.).
Source attribution and extreme event attribution seek to address these two elements. However, scientific studies on these topics rarely encompass the full causal chain ('end-to-end attribution') and are often question-dependent, meaning that results can be heavily influenced by the choice of event definition and different methodologies may produce differing results, despite being equally valid from a scientific point of view. Aside from the fact that it will be difficult for plaintiffs to meet a 'but for' test of causation (in jurisdictions where this is required), defendants may deny or diminish their liability by highlighting the role of natural variability or other causal factors, and by challenging the foreseeability of the losses for which damages are being claimed.
The quality of the scientific evidence relied on by plaintiffs is also an issue. Studies are often not peer-reviewed, nor are they conducted with a view to the specific situation being dealt with in the legal proceedings. Defendants can therefore question the relevance and reliability of the underlying data, assumptions, climate models and methods applied.
4. CONCLUSION
Courts are already showing a willingness to accept the findings of climate change attribution as evidence and attribution science looks set to become an increasingly central feature of climate change litigation against companies in the future. Due to the current limitations of attribution analysis, especially with respect to source attribution and extreme event attribution reports and studies in that area likely do not meet the required standard of evidence under various national laws.
However, as more data is gathered and scientific methods perfected, attribution science is likely to become more definitive and may in time be deemed a sufficient basis to establish causation and civil liability of companies.
Originally published
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