States have legal duty to cut greenhouse emissions, says top maritime court

Greenhouse gases are pollutants that are wrecking the marine environment, and states have a legal responsibility to control them, an international court has stated in a landmark moment for climate justice.

Wealthy nations must cut their emissions faster than their developing peers, the court also decided.

The statements were part of an advisory opinion on climate change issued on Tuesday by the international tribunal for the law of the sea (Itlos). The tribunal is responsible for interpreting and upholding the 1982 UN convention on the law of the sea (Unclos), an international treaty representing 169 countries.

It is the first time such a document has been issued by an international court.

Eselealofa Apinelu, the former attorney general of Tuvalu and now High Commissioner to Fiji said it was a historic moment for small island states in their quest for climate justice. “It is an important first step in holding the major polluters accountable for the sake of all humankind.”

The opinion was requested by the Commission of Small Island States on Climate Change and International Law (Cosis), a group of nine Caribbean and Pacific island nations led by Antigua and Barbuda and Tuvalu, who are particularly vulnerable to climate breakdown and had become frustrated with the pace of international talks.

In its unanimous opinion, the tribunal stated that the oceans are warming and becoming more acidic as a direct result of carbon dioxide emitted from human activities, resulting in harm to living resources and marine life, hazards to human health and hindrance to marine activities such as fishing.

Although Unclos does not specifically refer to climate change, the tribunal concludes that anthropogenic greenhouse gases are clearly a form of pollution, and states that have signed the convention are therefore legally required to prevent, reduce and control it “by all means necessary”.

In their submissions to the tribunal, most countries accepted that greenhouse gases were a form of pollution, but they disagreed on how exactly governments should have to respond to that threat.

The tribunal says their actions should be decided “objectively” based on the best available science. “In determining necessary measures, scientific certainty is not required,” it says.

It adds that states have a “stringent” duty of due diligence, under which they have to put in place legislation, administrative procedures and enforcement mechanisms to regulate activities emitting greenhouse gases – including from the private sector.

Wealthy countries such as the UK and Australia, as well as those in the EU, had contended that climate change was already being dealt with at an international level through the United Nations Framework Convention on Climate Change, which resulted in the Paris agreement in 2015. Under this agreement, countries set their own climate targets and there is no international mechanism for ensuring that they stick to them.

But the tribunal said following the Paris agreement was not enough; the law of the sea imposed specific legal obligations on states and there were consequences for those that did not comply.

Joie Chowdhury, a senior attorney at the Center for International Environmental Law, said: “It’s the first time an international court has unequivocally affirmed that states do not have unfettered discretion, but specific obligations under international law to act urgently, ambitiously and equitably, to protect oceans from the drivers and impacts of climate change.”

The tribunal also says that wealthier nations must shoulder a bigger portion of the burden and support developing states with funding and technical assistance.

Payam Akhavan, a professor of international law at the University of Toronto and a legal adviser to Cosis, said he hoped that states meeting at the Cop29 climate conference in November and subsequent international climate talks would “revisit the assumptions that they have had about whether their conduct is sufficient to meet their international obligations”.

As well as cutting emissions from land-based sources, the tribunal says states must control greenhouse gases from international shipping and aviation. This was welcomed by Opportunity Green, an NGO that tries to hold the shipping industry accountable for its emissions.

Itlos is the first of three courts to produce an advisory opinion on climate change. The international court of justice (ICJ) was tasked last year with giving its view on states’ legal duties on the climate emergency, and the inter-American court of human rights held the first of several hearings into its own opinion in April.

While the document is not in itself legally binding, such opinions are highly influential and set the framework for future climate lawsuits.

And although not every country has signed the convention on the law of the sea – the US is notable by its absence – the Itlos opinion is expected to influence that being produced by the ICJ, to which states are now submitting their final written statements.

Gaston Browne, the prime minister of Antigua and Barbuda, said he hoped the three parallel opinions would create a “harmonious message” that it was time for action. He added: “We stand at a pivotal moment in history.”