The evaluative foundations in juridical practice: How we justify “best available science” to push climate justice forward
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By Junhua Qu and Lan Wu
EvalYouth China
Climate injustice is nowhere more visible than in small island states. As the canary in the coal mine of climate catastrophe, they are particularly vulnerable to the impacts of climate change on the marine environment.
As for the formal request submitted by the Commission of Small Island States (COSIS) in December 2022, the International Tribunal for the Law of the Sea (hereinafter “the Tribunal”) issued Advisory Opinion No. 31 (hereinafter “the Advisory Opinion”) on May 21, 2024. Small island states had asked the Tribunal to clarify what legal obligations countries have under the UN Convention on the Law of the Sea (UNCLOS, hereinafter “the Convention”).
The Advisory Opinion concluded that anthropogenic greenhouse gas (GHG) emissions can constitute pollution of the marine environment. States therefore have a stringent due-diligence obligation to take all necessary measures to prevent, reduce, and control marine pollution, including ocean warming, rising sea levels, and acidification.
For the first time at the international judicial level, the Tribunal addressed the intersection of climate change and the law of the sea. The evaluative method in the Advisory Opinion helped clarify basic scientific facts and ground “necessary measures” according to the best available science. It underlined that scientific uncertainty cannot justify inaction where serious or irreversible harm is at stake. Evaluation here bridges the gap, enabling courts to advance climate justice through juridical practice.
The evaluative work behind “best available science”
The Advisory Opinion establishes a verified causal chain more than “climate change is real”. It traces anthropogenic GHG emissions from atmospheric accumulation through ocean absorption to concrete marine harms (ocean warming, acidification, and deoxygenation) to determine whether such emissions qualify as “pollution” under the Convention and whether States have fulfilled their obligations. As the Tribunal deeply recognized that “the phenomenon of climate change is central to the Request and the questions contained therein necessarily have scientific aspects”,[1] an inherently evaluative approach has been adopted. By its extensive and structured engagement with scientific evidence, the Tribunal linked greenhouse gas (GHG) emissions to marine harm, to determine whether such emissions constitute “pollution” under the Convention and whether states have met their obligations under Part XII.
The Tribunal is a judicial body established under the Convention, to interpret and apply the Convention (Article 288(1)) and “other rules of international law not incompatible with this Convention” (Article 293).[2] It does not generate scientific knowledge itself, nor its advisory function does not qualify as an “evaluation” in the technical sense used by the OECD Development Assistance Committee (DAC) or the World Bank.[3]
This is why the Intergovernmental Panel on Climate Change (IPCC) mattered. Their assessment reports, as a systematic evaluation of global climate science, are almost universally accepted by participants in the proceedings at the Tribunal.[4] The Tribunal first summarized substantive conclusions, such as the deleterious effects of anthropogenic GHG emissions. But the Tribunal did more than repeat scientific conclusions. It paid attention to how the IPCC assesses evidence, including its use of confidence levels and likelihood language to communicate certainty and uncertainty.[5] By this epistemic evaluation, the Tribunal treated the IPCC as a factual basis for legal reasoning. “Best available science” now became more than a general reference as the Tribunal effectively evaluated whether state conduct met the standard under the Convention Article 194.
The Tribunal therefore demonstrates evaluative legal reasoning, as it assesses the credibility of evidence, verifies causal links between GHG emissions and marine harm, as well as judge the significance of state conduct under the Convention.[6] In this sense, evaluation is not what the tribunal does, but it is the rational infrastructure that makes the tribunal’s climate justice reasoning possible.
Scientific evidence as evaluative enabler of the five pillars of climate justice
Climate justice in international law requires more than moral commitment, as well as requiring evidence. The Advisory Opinion demonstrates how scientific evaluation makes climate harm legally visible, responsibility measurable, and legal obligations adaptive. This triple evaluative function operationalizes climate justice without reducing it to the abstract principle of climate justice. The UNU Institute for Environment and Human Security identifies five key dimensions of climate justice[7]: recognitional, procedural, distributive, restorative and transformative justice. Each dimension represents a different just way in climate governance.[8] These dimensions should be adopted in law with an evidentiary infrastructure instead of abstract moral aspirations.
The Advisory Opinion illustrates precisely how evaluation furnishes this infrastructure:
Recognitional justice: The Tribunal’s quantification of marine harm renders small island states’ vulnerability legally visible. Evaluation thus grants vulnerable actors’ epistemic authority to define climate harm on the global stage.
Procedural justice: By relying on IPCC findings, the Tribunal imports evaluative norms of transparency and systematic review into the judicial sphere, reinforcing participatory and accountable climate governance.
Distributive justice: IPCC metrics theoretically link emissions to marine harm, satisfying OECD-DAC and World Bank evaluative standards. Yet this does not mean that scientific attribution automatically produces legal obligation or material remedy. Evaluation here in the Advisory Opinion thus serves a dual function: measuring causal responsibility while exposing the accountability gap between scientifically established harm and politically realized reallocation.
Restorative justice: The IPCC’s projections of irreversible change establish the forensic foundation required for reparation. Based on that, the Tribunal’s evaluation of damage magnitude, duration and irreversibility creates the legal predicate for restorative finance and institutional remedies.
Transformative justice: By linking the obligations under the Convention to the IPCC’s iterative cycles, the Tribunal gives international law a more adaptive character. States’ climate-related duties should not remain fixed at a single point in time, compelling continuous reassessment as new risks emerge. The Convention is thereby transformed from a static treaty into an evidence-based governance framework that simultaneously advances climate action and a fairer international community.
The enabling processes are shown below:
Historical legal pathway: how science interacted with the international environmental law system
The role of scientific evidence in climate advisory opinions did not emerge in a vacuum. International environmental law has long used assessment to act under scientific uncertainty. A useful precedent is the ozone regime.
The ozone regime is remarkable as it happened to first address a long-term problem which effects are not evident for decades hence.[9] It required decisions based on probabilities, flexibility of being adapted to new sciences assessments and maximum international cooperation.
The 1985 Vienna Convention created a framework for scientific cooperation, systematic observation, and information exchange. The 1987 Montreal Protocol went further by institutionalizing periodic assessment. Article 6 requires parties to review control measures based on available scientific, environmental, technical, and economic information.[10] The history shows that evaluation can be part of law-making itself as it identifies risk, justifies precautionary action, and allows legal obligations to evolve as knowledge improves. The 1990 London Amendment strengthened controls on CFCs and halons and expanded regulation to additional substances based on “the most recent scientific evidence” at that time.[11]
In this sense, the Tribunal concluded that States must take all “necessary measures” to control marine pollution associated with anthropogenic GHG emissions and said that what constitutes necessary measures “should be determined objectively” taking into account, among other things, “the best available science”.[12] It now helps define the content of state obligations.[13] The Tribunal also affirmed that duties of scientific cooperation under the Convention, also apply to GHG-related marine pollution.[14] The tribunal act anticipatory as it urged States to take preventive measures even in the absence of absolute scientific certainty.[15]
Conclusion: evaluation for climate justice
The Advisory Opinion is not merely a legal document about the law of the sea. It reveals something far more useful for evaluators: it shows how rigorous, credible evaluation of evidence can turn abstract vulnerability into enforceable justice.
For evaluators, the Advisory Opinion offers three interconnected lessons:
Evaluation as a recognition tool. Just as IPCC reports made small island states visible to the court, evaluations can make differential vulnerability visible across gender, geography, age, disability, or displacement status, performing recognitional justice in the process.
Process integrity builds credibility. The Tribunal trusted the IPCC not merely for its conclusions but for its transparent, peer-reviewed, multi-stakeholder procedures. This illustrates a broader principle: the legitimacy of evidence depends on the integrity of the producing process. For evaluators, the lesson is that credible evidence depends on methods suited to the purpose. Where participatory evaluation is appropriate, credibility can be further strengthened by engaging affected communities in defining indicators, interpreting findings, and validating recommendations. In that case, the process remains open to scrutiny and methodological challenge.
Evaluation should remain responsive to new evidence. The Advisory Opinion clarified that the measures expected of States must reflect the best available science as it develops. It reads the Convention considering evolving science, reminding us that evaluation should not be limited to end-of-project reporting. For evaluators, the parallel is limited but useful: evaluation should create opportunities to revisit findings and assumptions when conditions change.
Ultimately, the ITLOS Opinion reminds us that evaluation is not a back-office compliance exercise. When it is independent, credible, and useful, evaluation becomes part of the infrastructure of justice. The emerging hierarchy of scientific evidence in climate litigation places IPCC Assessment Reports at the top following the Advisory Opinion.[16] For future evaluation practice, the challenge is to balance scientific authority with responsiveness to emerging evidence, so that courts do not overlook fast-developing climate harms.
Junhua Qu is an Energy Analyst at Pratus Group. Her professional experience spans energy modelling, climate policy analysis, carbon markets, and biodiversity protection across both NGO and private-sector contexts. With a continued interest in energy transition, climate governance, and SDG evaluation, she has participated in SDG evaluation workshops organized by EvalYouth China.
Dr. Lan Wu is a Lecturer at the Faculty of Law, Ocean University of China, where she teaches environmental and natural resources law. Her research focuses on the legal and regulatory frameworks essential to facilitating the clean energy transition amidst the global climate crisis. Dr. Wu holds a PhD from The Chinese University of Hong Kong and previously served as an Energy and Climate Fellow at UNDP China. Her recent work includes identifying regulatory barriers and crafting innovative legal solutions to advance climate action and sustainable energy governance. She has published book chapters on related topics with De Gruyter and Palgrave Macmillan.
AI Disclaimer : AI tools were used solely to bring the blog to the required length and to correct grammatical issues. The blog's content, ideas, and narrative were authored by the human writer, not generated by AI.
References
[1] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 46.
[2] UNCLOS Article 286-288 (1), 293 and Article 16 and 21 of Annex VI.
[3] Organisation for Economic Co-operation and Development (OECD). “Evaluation Criteria.” Development Co-operation, Evaluation and Effectiveness, https://www.oecd.org/en/topics/sub-issues/development-co-operation-evaluation-and-effectiveness/evaluation-criteria.html, OECD, accessed 24 May 2026; World Bank Group. World Bank Group evaluation principles. https://ieg.worldbankgroup.org/world-bank-group-evaluation-principles, accessed 24 May 2026.
[4] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 51.
[5] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 49, 50, 54-61.
[6] Organisation for Economic Co-operation and Development. (2023). Glossary of key terms in evaluation and results-based management for sustainable development (2nd ed.). OECD Publishing. https://doi.org/10.1787/632da462-en-fr-es.
[7] See for example,Weiss, E.B. In Fairness to Future Generations, Hotei Publishing: Leiden, The Netherlands, 1988; Schlosberg, D. (2004). Reconceiving Environmental Justice: Global Movements And Political Theories. Environmental Politics, 13(3), 517–540; Schlosberg, David and Lisette B. Collins. From environmental to climate justice: climate change and the discourse of environmental justice. Wiley Interdisciplinary Reviews: Climate Change 5 (2014) 359–374; Newell, P., Srivastava, S., Naess, L. O., Torres Contreras, G. A., & Prize, R. (2021). Toward transformative climate justice: An emerging research agenda. Wiley Interdisciplinary Reviews: Climate Change, 12(6).
[8] United Nations University Institute for Environment and Human Security. (2025). 5 key dimensions of climate justice. https://unu.edu/ehs/article/5-key-dimensions-climate-justice, United Nations University, accessed 24 May 2026.
[9] Vienna Convention for the Protection of the Ozone Layer. (n.d.). https://legal.un.org/avl/ha/vcpol/vcpol.html
[10] Laboratory, N. C. S. (n.d.). NOAA CSL: Scientific Assessment of Ozone Depletion: 2014. https://csl.noaa.gov/assessments/ozone/2014/preface.html.
[11] Cordis, C. (1992, February 25). Montreal Protocol: Amendment increases CFC/halon controls. CORDIS | European Commission. https://cordis.europa.eu/article/id/748-montreal-protocol-amendment-increases-cfchalon-controls/de.
[12] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 243.
[14] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 312–320.
[15] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Advisory Opinion, 21 May 2024, para 212 and 213; Torre-Schaub, M. (2024, December 19). Why climate science matters for international Law. Climate Law Blog. https://blogs.law.columbia.edu/climatechange/2024/06/06/why-climate-science-matters-for-international-law/.
[16] Walker-Crawford, N., Reyes, J. J., Petkov, N., Palazzo Corner, S., Grantham Research Institute on Climate Change and the Environment, & Grantham Institute - Climate Change and the Environment. (2026). Science in the courtroom: evidentiary needs in climate litigation. Grantham Research Institute on Climate Change and the Environment, London School of Economics and Political Science and Grantham Institute - Climate Change and the Environment, Imperial College London. https://doi.org/10.21953/researchonline.lse.ac.uk.00137472.
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