I finished my Master’s in (international) law only ten years ago. Yet, it seems the next generation of law students are now graduating in subjects we could not even have imagined when I was in law school. Artificial intelligence (AI) law is an obvious example, but climate law is another emerging field that stands out to me in particular. “Back in my day”, we could choose International Environmental Law as an elective. It offered a broad overview of principles, declarations and agreements addressing issues such as pollution and biodiversity loss. I remember feeling rather underwhelmed by the course, as it seemed to lack the kind of tangible, enforceable obligations I had encountered in other areas of international law. Today, that picture looks different. International environmental law seems to have evolved into a broader and more robust field, encompassing emerging areas such as climate law.
Climate law, and the related wave of climate litigation, refers to the legal frameworks, policies and court actions aimed at addressing climate change. It includes rules on greenhouse gas emissions, renewable energy mandates and adaptation measures, as well as lawsuits holding governments and corporations accountable for failures to mitigate or adapt to climate risks. What makes the field particularly dynamic is the way it intersects with human rights, trade law and investment law. In just a few years, climate change has moved from scientific reports into courtrooms around the world. International tribunals such as the International Court of Justice (ICJ) and the International Tribunal for the Law of the Sea (ITLOS) have been asked to articulate, in clear legal terms, what States are required to do in response to human-made climate change.
So, if the world’s highest courts have spoken, is the legal battle won? Not quite. Advisory opinions have clear limits. They interpret the law, but they do not order specific States to change their policies or pay compensation. Nor do they, by themselves, give individuals direct access to the ICJ or ITLOS. In other words, advisory opinions set the rules of the game, but they do not play the game for us. The International Court of Justice has clarified States’ obligations under international law to tackle climate change, much like the International Tribunal for the Law of the Sea (ITLOS) did before it. Yet these opinions are non-binding guides, not direct orders with immediate enforcement. For binding case law that actually forces change, we turn to national courts.
That dynamic is visible in two recent cases from one city: The Hague (the Netherlands). The ICJ, which resides in The Hague, issued its advisory opinion on climate change in July 2025, outlining states’ duties at the global level. Those same duties were taken up last week by the District Court of The Hague in the Bonaire case, where residents of the small Dutch Caribbean island challenged the Dutch state for failing to protect them against climate impacts. In their ruling, the The Hague District Court found violations of human rights by the government of The Netherlands and explicitly relied on the ICJ’s advisory opinion to order more ambitious emission reductions and concrete adaptation measures tailored to Bonaire’s specific vulnerabilities, including rising sea levels and extreme heat. The case shows how international legal guidance can be translated into enforceable obligations under domestic law. The Bonaire judgment is not an isolated development. Climate litigation of this kind has been growing worldwide for years, with an estimated 400+ climate change-related cases in various courts.
If you are interested in how climate science, international opinions from ICJ and ITLOS, and domestic rulings like the Bonaire case fit together, the rest of this piece offers a deeper dive into those building blocks of climate litigation.
From science to law: the role of the Intergovernmental Panel on Climate Change (IPCC)
To understand how international climate obligations are articulated in legal terms, one key actor sits in the background: the Intergovernmental Panel on Climate Change (IPCC). The IPCC is a UN body that does not conduct its own experiments. Instead, thousands of scientists review and synthesise existing research to produce periodic assessment reports on how the climate is changing, what drives those changes, and what impacts can be expected. These reports have consistently concluded that greenhouse gas emissions from human activities are “unequivocally” driving global warming, and that the most severe impacts, i.e. flooding, heatwaves, sea level rise and ocean change, are often borne by communities that have contributed least to the problem.
When international courts have been asked to address climate change, they have treated IPCC findings as the most authoritative scientific source available. In doing so, they have effectively translated climate science into legally relevant facts: anthropogenic emissions are causing serious harm; vulnerable states and communities are disproportionately affected; and limiting warming to around 1.5°C is not merely a political aspiration, but a necessary benchmark for assessing whether States are meeting their legal obligations.
What international courts have said so far
Both the International Court of Justice (ICJ) and the International Tribunal for the Law of the Sea (ITLOS) were approached through the advisory opinion procedure. In this process, a court responds to legal questions submitted by States or UN bodies. There is no dispute between parties, no binding order to change policies or pay compensation, and no formal “winner” or “loser”. Advisory opinions are therefore non-binding. Nevertheless, they carry significant legal authority: they clarify the content of existing international law and reflect the collective view of all judges of the court.
In its advisory opinion requested by a group of small island States, ITLOS concluded that greenhouse gas emissions can qualify as “pollution of the marine environment” under the UN Convention on the Law of the Sea. This finding triggers a stringent duty of due diligence. States must take all necessary measures to prevent, reduce and control such pollution, act on the basis of the best available science, and assess their conduct against the objective of limiting warming to 1.5°C.
The ICJ, for its part, confirmed that States have obligations under general international law and relevant climate treaties to prevent significant climate harm. It made clear that failure to act consistently with the 1.5°C benchmark may engage international responsibility. Both courts explicitly recognised the unequal distribution of emissions and impacts: some States contribute far more per capita, while the gravest consequences are often experienced by countries and communities with minimal historical responsibility.
Climate litigation at home: turning clarification into enforcement
While these advisory opinions clarify what international law requires, they do not by themselves compel States to act. That translation work happens at the national level. Zooming in from The Hague to domestic courts reveals a long-standing and growing body of climate litigation. Researchers now count hundreds of climate cases worldwide, spanning trial courts, supreme courts and constitutional courts. Claimants rely on a wide range of legal tools, human rights law, tort law, constitutional duties and environmental legislation, to argue that governments and companies are failing to meet their obligations to prevent dangerous climate change.
The Bonaire case: international law applied at home
Last week [January 2026], a court in The Hague delivered judgment in a case brought by eight residents of Bonaire, together with Greenpeace Netherlands. Bonaire is a low-lying Caribbean island that forms part of the Kingdom of the Netherlands and is highly exposed to sea level rise, stronger storms and coral reef loss. The claimants argued that the Dutch government was failing both to reduce emissions adequately and to protect the island’s inhabitants from the foreseeable impacts of the climate crisis.
The court agreed, finding that the State was acting unlawfully towards Bonaire’s residents. It ordered the Netherlands to draw up and implement a specific climate adaptation plan for Bonaire by 2030 at the latest, and to set new binding emission reduction targets for the Dutch economy within 18 months, based on a fair share of the remaining global carbon budget consistent with the 1.5°C limit. The judgment also criticised the unequal treatment between residents of the European Netherlands and those living on Bonaire, framing this disparity as discriminatory and incompatible with human rights obligations.
Why this matters
The significance of the Bonaire case lies not just in its outcome, but in what it shows about the interaction between international and national legal systems. It demonstrates how abstract international obligations, clarified by the ICJ and ITLOS and grounded in IPCC science, can be translated by domestic courts into concrete, enforceable requirements: timelines, plans, targets and standards of fairness. It also highlights climate justice within a single State, where residents of a distant, formerly colonised territory invoke national courts to demand protection equivalent to that enjoyed in Europe.
Finally, timing matters. The Bonaire judgment was delivered after the major advisory opinions of the ICJ and ITLOS, and it already reflects the growing tendency of domestic courts to draw on international case law and climate science when assessing whether States are doing enough. Climate litigation now operates on two interconnected tracks: international clarification and domestic enforcement. As the Bonaire case illustrates, it is at the national level that those clarified obligations most quickly translate into changes that affect people’s daily lives.
Disclaimer: The views and opinions expressed in this article are solely those of the author, Eva van Heukelom, and do not necessarily reflect the official policy or position of any affiliated organisations, institutions, or entities. The analysis and conclusions presented are based on the author’s independent research and interpretation. While every effort has been made to ensure the accuracy and reliability of the information provided, no guarantee is given regarding its completeness or applicability to any particular situation.
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