THE LAW AND SCIENCE OF CLIMATE CHANGE ATTRIBUTION
By Michael Burger, Jessica Wentz and Radley Horton
The evolving field of climate change detection and attribution science helps to shape both our physical understanding of how the global climate system is changing and discussions pertaining to responsibility and accountability for the impacts of climate change. Confronted with a growing body of research linking increases in greenhouse gas emissions to specific harmful impacts, governments, courts, and private actors are addressing critical legal questions such as whether governments are doing enough to mitigate and adapt to the effects of climate change and whether corporations can be held liable for their contributions to the problem. This Article describes how climate change detection and attribution science is now and may in the future be used in policymaking and litigation. We focus primarily on litigation, as this is one key context in which attribution science is influencing the legal discourse on “responsibility” for climate change. Some of our key findings are: • The existing body of detection and attribution research is sufficiently robust to support the adjudication of certain types of legal disputes. But there are also complicating factors which can make it difficult to identify a clear causal chain between a particular emission source and specific harms or impacts associated with climate change. Ultimately, the extent to which the science can support legal claims will depend on many factors, such as the nature of the claim, the identities of the plaintiffs and defendants, and the nature of the alleged injuries. • Many observed physical impacts such as sea level rise, melting permafrost, and ocean acidification can be attributed to anthropogenic climate change with high confidence. Consensus confidence levels are currently lower for other impacts, such as extreme events, public health outcomes, economic losses, and ecosystem degradation. There is a growing body of extreme event and impact attribution studies finding a causal connection between impacts such as heat-related mortality and anthropogenic influence on climate change. • Once an impact has been attributed to anthropogenic climate change, it can also be attributed to specific emission sources on a proportional basis. This calculation may involve estimating the proportional contribution of the source to global greenhouse gas emissions, and using that to extrapolate the proportional contribution of the source to the impact. However, source attribution is not a purely objective quantitative exercise. There are normative questions implicated in the process of determining who is responsible for what emissions. • Attribution science plays an important role in lawsuits seeking to compel national governments to take action on climate change. In several foreign cases, plaintiffs have successfully used attribution science to demonstrate that a government’s failure to regulate greenhouse gas emissions at adequate levels endangered the public health and welfare of citizens within the country, and thus the government had violated its duty of care to its citizens. Attribution science is also central to the plaintiffs’ claims for standing, constitutional harm and violations of the public trust doctrine in Juliana v. United States. • Lawsuits seeking to hold corporations liable for their contribution to climate change have met with jurisdictional, justiciability, and procedural obstacles, and to date have not faltered due to any limitations in the science. For example, some U.S. courts have held that climate-related claims are either displaced by the Clean Air Act or should be handled by other branches of government based on separation of powers principles. The science may be strong enough to support a finding of liability if plaintiffs in pending and future cases overcome these initial hurdles and if judges apply traditional tort principles when evaluating the merits of these claims. • The scientific community can support applications of attribution research, such as the use of this research to inform loss and damage negotiations and judicial determinations of liability for climate change impacts. Such support may involve continuing to expand and improve upon existing attribution research, including in currently underrepresented geographic regions and with regards to impacts experienced in the present; communicating findings clearly and in an accessible format; engaging with stakeholders to help them understand findings; and linking individual studies to other research that helps to flesh out the causal chain from emissions to impact. …. Policymakers, judges, and litigants can also improve their understanding of the science and expand the analytical approaches they use to evaluate the legal and normative implications of the science when making judicial or policy determinations. Below, we summarize our analysis and findings in greater detail.