Climate Change an 'Existential Threat', Says World's Top Court

The International Court of Justice delivered a landmark opinion on the obligations of states in respect of climate change, marking a historic win and a turning point for the world’s most vulnerable nations and communities.

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Climate change poses an “existential problem of planetary proportions,” threatening “all forms of life and the very health of our planet,” the world’s top court has said.

The International Court of Justice (ICJ), the principal judicial organ of the United Nations, delivered its long-anticipated advisory opinion on the obligations of states in respect of climate change on Wednesday. It ruled that government actions driving climate change are illegal and states are legally bound to cut their emissions and compensate vulnerable nations for the harm they have caused.

Presenting the opinion at the Peace Palace in The Hague, the court’s President Yuji Iwasawa said greenhouse gas emissions are “unequivocally” caused by human activities.

“The consequences of climate change are severe and far-reaching. They affect both natural ecosystems and human populations. These consequences underscore the urgent and existential threat posed by climate change,” said Judge Iwasawa.

Judge Yuji Iwasawa, President of the International Court of Justice. Photo: UN Photo/ICJ-CIJ/Frank van Beek. Courtesy of the ICJ.

Before the court’s 15 judges were two fundamental questions: What are states’ obligations under international law to address climate change for present and future generations? And what are the legal consequences under these obligations for states failing to do so?

Judge Iwasawa said the questions “represent more than a legal problem: they concern an existential problem of planetary proportions that imperils all forms of life and the very health of our planet.”

What follows are some of the main arguments presented by the court.

Clear Legal Duties Under Entire Corpus of International Law

In analyzing states’ obligations under international law, the court considered the entire corpus of international law, including the UN Charter, climate change treaties (the UN Framework Convention on Climate Change, the Kyoto Protocol and the Paris Agreement); other environmental treaties, and international human rights law. This contradicts major polluters’s arguments that UN climate agreements serve as the sole or principal framework for interpreting the extent of states’ climate responsibilities.

The judges concluded that states are required under international laws to reduce emissions, prevent harm, and collaborate to safeguard vulnerable populations. They also stressed that these obligations encompass the full range of activities resulting in greenhouse gas emissions, from fossil fuel usage to extraction, subsidies and regulatory oversight.

Lex Specialis

Importantly, the court rejected the lex specialis argument raised by many developed states, which suggests that the specific treaty regimes related to climate change – such as the UNFCCC and the Paris Agreement – should be considered as the primary or only source of law for determining states’ obligations in relation to climate change.

Big polluters have repeatedly envoked the argument to claim that climate agreements protect them from accountability for climate harms, Sébastien Duyck, Senior Attorney in the Climate & Energy Program at the Center for International Environmental Law, pointed out.

Paris Agreement

In relation to the Paris Agreement, the court affirmed recognized the 1.5C target to be the only relevant limit and recognized that the climate treaty establishes “stringent” mitigation obligations for states to protect the climate and other parts of the environment from anthropogenic greenhouse gas emissions.

It also dismissed an argument put forward by big polluters that national climate action plans, known as Nationally Determined Contributions (NDCs), are discretionary. Instead, the court affirmed that NDCs – which states are required to update every five years – must collectively be capable of realizing the objectives of the agreement.

“The court concludes that rather than being entirely discretionary, as some participants argued, NDCs must satisfy certain standards under the Paris Agreement. All NDCs … must, when taken together, be capable of realizing the objectives of the Agreement which is set out in Article 2,” said Judge Iwasawa.

Importantly, the court noted that obligations under customary international law still apply to countries not party to specific UN climate treaties. This seems to be directed at the US, which withdrew from the Paris Agreement earlier this year.

Human Rights

In regards of human rights, the court affirmed that the human right to a “clean, healthy, and sustainable envirnoment” is “essential” for the enjoyment of human rights – something that developing countries have long campaigned for.

“The environment is the foundation for human life, upon which the health and well-being of both present and future generations depend. The protection of the environment is a precondition for the enjoyment of human rights, whose promotion is one of the purposes of the United Nations as set out in Article 1, paragraph 3, of the Charter,” said Judge Iwasawa, reaffirming a universal right first recognized by the UN General Assembly in 2022.

Timeline of the International Court of Justice Advisory (ICJ) Advisory Opinion on climate change. Image: Martina Igini/Earth.Org.

Young activists from various climate change-battered Pacific Island nations organized under the Pacific Island Students Fighting Climate Change (PISFCC) launched a global campaign for an advisory opinion back in 2019 as they seeked climate justice and legal pathways to hold big polluters accountable for their actions. For them, an advisory opinion is “the most authoritative and constructive route available for an independent clarification of the legal implications of climate change under international law.”

The Pacific Islands are at the forefront of climate change, threatened by a triple whammy of accelerating sea level rise, ocean warming and acidification despite being responsible for less than 1% of total global greenhouse gas emissions.

Earth.Org’s Editor-in-Chief Martina Igini interviews Vishal Prasad, Director of PISFCC.

“Today the world’s smallest countries have made history,” said Vishal Prasad, Director of PISFCC. “The ICJ’s decision brings us closer to a world where governments can no longer turn a blind eye to their legal responsibilities. It affirms a simple truth of climate justice: those who did the least to fuel this crisis deserve protection, reparations, and a future. This ruling is a lifeline for Pacific communities on the frontline.” 

Grounded in binding international law, the opinion is set to spark a chain reaction that accelerates climate litigation on a global scale.

“When a court like the ICJ recognizes new connections between conduct and legal norms, like the idea that failing to curb fossil fuels-related emissions can violate international legal obligations, it does not stop there. That recognition opens the door for further legal claims,” said Senior Attorney Sebastien Duyck.

World’s Top Courts Increasingly Involved

A growing number of cases, mostly involving government defendants but also corporate defendants, are reaching top courts such as supreme or constitutional courts, according to a recent report by London-based Grantham Research Institute on Climate Change and the Environment.

The ICJ is the third international court asked to clarify states’ obligations on climate change in recent years, alongside the Inter-American Court of Human Rights (IACtHR) and the International Tribunal on the Law of the Sea (ITLOS).

In its May 2024 advisory opinion, the ITLOS – a UN court on maritime law – said carbon emissions can be considered a marine pollutant, and furhter stated that countries must “take all necessary measures to prevent, reduce and control marine pollution from anthropogenic [greenhouse gas] emissions.”

The ruling also made clear that the work of defining countries’ obligations is not limited to the Paris Agreement or the UNFCCC – the UN body on climate change, something that major polluters like the US and China have repeatedly contested while also arguing against courts taking climate-related decisions.

Meanwhile, the IACtHR – Latin America’s top human rights court – ruled that states and corporations have binding obligations under international law to address the climate crisis as a human rights emergency, and placed irreversible climate harms on the same level as internationally-recognized crimes like genocide and torture. Notably, a section of the opinion addressed environmental defenders, affirming states’ binding obligations not only to protect those who defend land, climate, and human rights but also to investigate those acts, punish those responsible, and ensure access to justice.

Experts described the IACtHR opinion as “the most important and progressive document yet released by an international court on the climate crisis.”  

While representing only a small proportion of climate cases, international courts’ opinions, while non-binding, carry significant legal weight and moral authority and are poised to shape the future of climate litigation, informing both domestic courts and international political processes.

The ITLOS ruling was referenced in at least one court proceeding in the UK, though its real impact on climate litigation has yet to be tested, according to the Grantham report.

Featured image: ICJ/ICJ Frank van Beek. Courtesy of the ICJ.

Check out our analysis of the ITLOS and IACtHR advisory opinions.