Expertise in climate litigation: production, uses and reception – PROCLIMEX

The innovative nature of the project lies in its interdisciplinary approach. Climate litigation had previously never been the subject of large-scale empirical research combining law, sociology, political science, economics, and climate science, based on a varied and complementary mix of methodologies. Primarily empirical, our methodology combined tools from sociology, political science, economics, and legal science: quantitative and qualitative analysis of the forms of scientific argumentation used; quantitative and qualitative text analysis and comparative study; quantitative and qualitative discourse and content analysis; lexicometric study, including written and oral procedural documents from trials; in situ observations during trials; semi-structured interviews with associative actors who have focused their actions on litigation, as well as with judges and lawyers; and data collection on the information, dissemination, and communication strategies implemented by NGOs around climate litigation.

In addition to their disciplinary work —conducted individually or with other project members from the same discipline— project members also carried out certain tasks in a transdisciplinary manner. Furthermore, research protocols were collectively designed and validated so that each member could build on the work of colleagues from other disciplines.

We thus combined micro-level approaches with more macro-level perspectives. Depending on their contributions, project members either worked monographically on a specific case, plaintiff (individual or NGO), or defendant (state or company), or adopted a comparative approach —either within or across countries— which is particularly relevant for identifying and analyzing arguments or reflecting on the role of legal doctrine. Researchers were able to draw on various databases developed as part of the project, enabling large-scale comparative analyses.

PROCLIMEX has yielded numerous results and key achievements. The project has helped to strengthen and develop the epistemic community around the themes of climate expertise and climate litigation. It confirmed the centrality of expert evidence issues in these trials. It highlighted the major role played by IPCC reports, as well as the importance of scenarios, figures and quantifications, whilst at the same time revealing the limited weight given to lay and experiential knowledge. The work carried out within PROCLIMEX sheds light on the role of the trial in mobilisation strategies. It also shows that whilst the use of expertise and the strategies employed in this regard have a decisive influence on the outcome of the trial, in turn, expertise is influenced and, in a sense, ‘framed’ by the development of climate trials. Among the main results and highlights, the PROCLIMEX team was selected for a week-long residential seminar at the Fondation des Treilles. V. Brunel joined the team in his capacity as a CNRS research engineer and O. Seigneury as a postdoctoral researcher. E. Falconnet and J. Banégas also joined the team as interns. Laura Canali defended her thesis on ‘The trial and climate change. A Study of the Juridical Formulation of Climate Law” and was appointed as a lecturer at the University of Nîmes. Two PhD grants were secured, one for C. Martini on “The Use of International Law in Climate Trials” (ADEME), and the other for B. Luczak on “Collective Mobilisations in the Digital Age. The case of climate struggles” (Aix-Marseille University). Liyuan Fan, a PhD student at the China University of Political Science and Law, spent 18 months at DICE on a doctoral fellowship focusing on expert evidence in climate litigation. M. Hautereau-Boutonnet joined an international group of researchers on climate litigation (visiting fellow at the British Institute of International and Comparative Law, London, June 2022). Sandrine Maljean-Dubois was invited for one month to the University of Hamburg for a research stay on expert evidence in climate litigation at the Futures of Sustainability Institute (January 2026).

Members of the PROCLIMEX project participated in and organised numerous academic events and produced a wealth of academic publications. The book edited by Ch. Cournil, ‘Experts and Legal Arguments: A Contribution to the Study of Climate Trials’ (DICE Éditions), was awarded the prize by the European Expertise & Expert Institute. Finally, the PROCLIMEX project’s final conference, held in Aix-en-Provence on 9 and 10 December 2025, was both a convivial occasion and a rich forum for scientific exchange. This will result in the publication of a book in English (Brill, accepted, 2027).

PROCLIMEX has helped to strengthen its members’ national and international collaborations. Discussions are currently underway regarding the continuation of the project through European initiatives.

Once the final report has been completed, the team is indeed considering continuing PROCLIMEX, with a slightly revised team, to pursue research in this rapidly developing field of study at an international level.

Several avenues could be explored, including:

- examining the scope of the advisory opinions issued by three, and soon four, international courts on this matter. Will they, like the Paris Agreement in its time, give new impetus to climate litigation? Will they drive its evolution?

- focusing on the growing number of international courts hearing such cases

- examining new types of litigation (adaptation, compensation for damages, etc.)

- focusing on the development of attribution science and its impact on litigation.

A growing number of actors and organisations are therefore now using litigation – in various ways and with varying degrees of success – as an instrument of contestation, mobilisation and beyond that, climate justice. In a context of renewed environmental democracy and participatory approaches (see the French Great Debate or National Climate Convention), the courtroom is one of the spaces that have recently been reclaimed, where citizens participate in the making of tomorrow's 'climate law'.
Many questions are raised by this new form of mobilisation for climate. Our team proposes to focus on the issue of expertise in these trials. Indeed, this is a fundamental issue in climate trials. For the plaintiffs, first, because they must argue a given point of view in favour of climate protection and have no choice but to appropriate knowledge and data from various sources, which are technical, complex and multidisciplinary (not only scientific, but also socio-economic and legal sources) and to build on this basis an expert system that is often enriched by lay knowledge (victims' testimonies, for example).
It is also fundamental for the outcome of the trial, which is largely determined by these expert systems at the heart of the claimants' legal strategies.
The main objectives of PROCLIMEX are as follows:
- To shed light on the judicial strategies of NGOs when they use litigation and the law as weapons against climate change, and on those of defendants in response (often States and corporations);
- To decipher the social uses of different sources of expertise in the context of initiatives supporting the judicialisation -i.e. the procedures used by the supporters of a cause to ensure that the courts appear able to provide an answer to the issues they denounce- of the climate cause;
- To highlight, through comparative analysis, the process of moving from scientific truth to legal truth by questioning the adaptation of procedural law and of the trial as an institution;
- To identify opportunities to strengthen the interface between scientists and policy-makers in climate matters in a context of climate emergency, thanks to focused efforts on scientific communication.