In May 2024, the International Tribunal for the Law of the Sea (ITLOS) gave its legal opinion. This was in response to a request from a group of small island nations who are deeply and immediately affected by climate change.

The Tribunal made a groundbreaking decision: greenhouse gas emissions from human activity are a form of marine pollution. This is a crucial step because it places the main cause of climate change directly under the rules of the UN Convention on the Law of the Sea (UNCLOS), a treaty ratified by most of the world’s countries.

Under these rules, countries must take “all necessary measures” to prevent, reduce, and control this pollution. The court clarified that this duty sets a “stringent” standard. It requires nations not just to make plans, but to create and enforce effective environmental laws and policies. These policies must be based on the best available science, explicitly linking them to the Paris Agreement’s goal of limiting global warming to 1.5°C.

The World Court’s Opinion: A Global Rulebook for Climate Action (July 2025)

Following the ITLOS ruling, the International Court of Justice (ICJ) issued an even broader opinion in July 2025. This came after a request from the UN General Assembly, championed by the island nation of Vanuatu and a global coalition of countries.

The ICJ confirmed that every country has a binding legal duty to protect the climate system. This duty comes not just from one source, but from a web of international laws, including treaties, international customs, and human rights, that work together and reinforce each other.

What Must Countries Do?

The ICJ outlined several key obligations for all states. These duties are not optional; they are legally required and demand a high standard of effort from every nation.

• Meet Climate Goals: Countries must take real, measurable action to help meet the 1.5°C temperature goal of the Paris Agreement. Their Nationally determined contributions (NDCs) must reflect the “highest possible ambition,” meaning each country must do its absolute best based on its capacity. These plans must also show clear progression and improvement over time.

• Prevent Harm: All countries have a fundamental duty to prevent significant harm to the climate system. This duty exists under customary international law, meaning it applies to every single state, regardless of which specific environmental treaties they have signed. It requires a “stringent” standard of care in all actions.

• Regulate Pollution: This duty covers government actions and failures to act, especially concerning fossil fuels, including production, use, and subsidies. It also means countries have a legal responsibility to regulate private companies within their borders to control emissions and prevent pollution.

• Protect Human Rights: The Court formally recognised the human right to a clean, healthy, and sustainable environment. It declared that a stable climate is essential for enjoying other basic human rights, such as the right to life, health, food, and water, all of which are threatened by climate-related disasters like floods, heatwaves, and droughts.

What Happens if Countries Fail to Act?

The ICJ made it clear that there are serious legal consequences for countries that fail to meet their obligations. A state that breaks its climate duties has committed an “internationally wrongful act” and is legally responsible for the damage it causes.

The state must then:

• Stop the harmful action (such as ceasing to fund a new fossil fuel project).

• Offer guarantees that it will not happen again.

• Provide full reparation for the injury caused. This can include restoring damaged ecosystems (restitution), paying financial compensation for losses (compensation), or formally apologising for the harm done (satisfaction).

Crucially, the court said these duties are owed to the international community as a whole (erga omnes). This means all countries have a recognised legal interest in protecting our shared climate and can hold a polluting state accountable, preventing other nations from simply looking away.

Why These Rulings Are Important

Together, these opinions from the ITLOS and ICJ provide an authoritative legal charter for global climate action. They strengthen the legal basis for lawsuits, brought by citizens, youth groups, and other nations, based on human rights and clarify the tough, non-negotiable duties states have.

By specifically mentioning fossil fuels and setting a high bar for action, these rulings are expected to heavily influence future legal challenges and drive more ambitious, science-based, and accountable climate policies around the world.