From evidence to legal obligation: The institutional and normative constraints on climate science in court

By Juliana de Augustinis

Climate lawsuits are bringing scientific evidence into the courtroom. Citizens, young people and NGOs challenging their governments’ climate policies often rely on IPCC reports, carbon budgets and mitigation pathways to argue that current efforts fall short. Like all scientific evidence, these findings rest on assumptions, involve uncertainty and leave room for choices, for instance about how to share the remaining carbon budget among countries.

Judges must then decide what weight to give this evidence when answering complex questions: how much, and how fast, must a country cut its emissions?

My new book, Science on Trial in Climate Litigation, examines how courts engage with this evidence through a comprehensive analysis of climate rulings across 14 countries. It shows that the path from evidence to legal obligation is far from a straight line. Across the rulings analysed, judges frequently treated the underlying science as authoritative. However, how far they engaged with it was often shaped by institutional and normative constraints, such as how courts understand their role in relation to governments, the procedures available to them, and the legal sources they treat as binding.

The Urgenda momentum

In 2019, the Dutch Supreme Court confirmed in Urgenda that the Netherlands’ climate policy breached the rights to life and to private and family life under the European Convention on Human Rights. It ordered the State to cut greenhouse gas emissions by at least 25% compared with 1990 levels by the end of 2020. To arrive at that number, the courts relied on reports from the Intergovernmental Panel on Climate Change (IPCC).

Urgenda inspired similar lawsuits around the world and raised broader questions, such as under what conditions scientific evidence informs judicial reasoning, and when it stays on the sidelines.

Answering them means looking beyond the landmark cases to a systematically selected body of rulings, and to the institutional settings in which they were decided.

What the rulings reveal

The book analyses cases challenging the adequacy of a government’s overall approach to reducing emissions, rather than sectoral mitigation policies. It examines 49 judgments issued between 2015 and 2022, across 14 jurisdictions, selected through a systematic search of leading climate-litigation databases. The study combines a systematic content analysis of the judgments, statistical analysis and a close reading of judicial reasoning. It also examines subsequent judgments up to May 2024.

The focus is on one specific kind of evidence, mitigation data, defined as science on who must reduce how much, and by when, to keep warming within safer limits. Four findings stand out.

• Science appears less often than expected. Nearly half of the judgments (45%) did not explicitly consider mitigation data at all.
• Explicit criteria for assessing evidence are uncommon. Only nine judgments explained criteria for evaluating mitigation data. In just three cases, courts used expert assistance to help assess its quality or meaning.
• Outcomes are moderate, not revolutionary. Almost half of the judgments dismissed the cases. Only seven rulings ordered governments to adopt stricter mitigation measures. Most recent European judgments examined were also unfavourable to claimants.
• References to mitigation data are associated with favourable outcomes, particularly in the United States and Canada. These outcomes include allowing a case to proceed or recognising a rights violation. Mitigation evidence also featured in five of the seven rulings ordering stricter mitigation, including Urgenda and Germany’s Neubauer.

These findings call for a shift in perspective on the actual state of climate litigation. Rather than asking why there are so many Urgenda-style lawsuits, the question becomes why so few of them have produced Urgenda-style decisions.

‘Across the globe, advocates for stronger action on climate change are turning to courts in search of judge imposed mitigation obligations. By engaging in an ambitious cross-jurisdictional empirical analysis of judicial decision-making, Science on Trial in Climate Litigation offers an invaluable new perspective on this burgeoning area of law.’

– Douglas A. Kysar, Yale University, USA

A way forward

If institutional concerns are a major obstacle, part of the response may lie in how courts design their remedies. Instead of imposing fixed emission targets, courts could use structural injunctions. Under this approach, courts would set overarching objectives consistent with the Paris Agreement’s 1.5°C goal and the best available science. Governments would design the detailed measures, ideally together with claimants and civil society, and courts would monitor progress through reporting duties and performance metrics. These arrangements could allow plans to be adjusted over time. Courts in India, South Africa and Brazil have used such approaches in other public interest cases, and they may offer lessons for older democracies. The book presents these as promising avenues for further investigation, not proven solutions to the institutional barriers identified.

The landscape is also shifting. In its 2024 KlimaSeniorinnen judgment, the European Court of Human Rights required States to base their climate targets on the best available science. Courts in the Global South have recently shown more openness to experts. Whether European courts will follow is one of the questions the book leaves open.

Who the book is for

The book is written for scholars and students of climate and environmental law, human rights, comparative constitutional law and empirical legal studies, as well as for judges, lawyers, NGOs, policymakers and scientists who want to understand how evidence travels into law.

Climate litigation is moving fast, towards corporate defendants, attribution science and new international rulings. If you want to know not only whether courts can rely on climate science but what shapes how they actually use it, and how that might change, I invite you to read on.

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Juliana de Augustinis is a postdoctoral researcher at the London School of Economics and Political Science (LSE). The book builds on her doctoral and postdoctoral research at Tilburg University, the Netherlands.