Governments can be held legally responsible for climate inaction, the world’s highest court said in a landmark decision on Wednesday, opening the door to a cascade of lawsuits. 

In the first decision of its kind, the International Court of Justice held that existing international law obliges all countries — whether they are party to the 2015 Paris climate accord or, like the United States, quitting the treaty — to fight global warming. 

Government inaction, including by failing to regulate companies polluting the climate, “constitutes an internationally wrongful act” that may result in legal consequences including “full reparation to injured states in the form of restitution [or] compensation.” 

Reading out the unanimous opinion, ICJ President Yuji Iwasawa highlighted the “the urgent and existential threat posed by climate change” and laid out a wide-ranging view of what could constitute such a breach. 

“The failure of a state to take appropriate action to protect the climate system from [greenhouse gas] emissions, including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses, or the provision of fossil fuel fuel subsidies, may constitute an internationally wrongful act which is attributable to that state,” he said. 

Climate justice advocates and countries particularly vulnerable to the effects of global warming celebrated the ICJ’s decision as a historic victory in their efforts to seek accountability from major polluters. 

While the opinion itself is nonbinding, it represents the judges’ interpretation of binding international treaties, existing conventions and customary law, and is expected to prove influential in future climate lawsuits. It also opened the door to countries hit by climate disasters and sea-level rise suing big polluters such as the U.S. and the EU.

The court held two weeks of hearings in December, in which many major polluters argued that the existing U.N. climate framework was sufficient as a legal tool. Many poorer, climate-vulnerable countries asked the ICJ for a more sweeping interpretation allowing for potential reparations. The court sided with the latter on Wednesday.

The opinion was the result of a years-long campaign by youth activists from the small island nation of Vanuatu, whose very survival is threatened by sea-level rise and supercharged storms. 

Efforts to fight climate change “aren’t aspirational ideas, as some would have it. The court has just confirmed they are binding duties,” said Ralph Regenvanu, climate minister of Vanuatu. “Today’s ruling, I’m sure, will also inspire new cases where victims around the world, in a legal sense, realize that they can claim their rights and seek accountability.”

Trump-proofing the climate fight

Vanuatu’s request for legal guidance had two parts: First, it asked the ICJ to clarify what countries’ obligations are under international law to reduce emissions; and second, what the legal consequences are for countries whose actions — or inaction — harms the climate. 

The judges noted that existing international climate treaties, such as the Paris Agreement and the overarching United Nations convention, set out “binding obligations” on countries to protect the planet’s climate system from greenhouse gas emissions that drive up the global temperature. 

Those obligations include adopting measures to reduce emissions and prepare for the impacts of climate change, with developed countries — responsible for the bulk of historical greenhouse gas pollution — taking a leading role in these efforts.

But similar obligations exist in unwritten customary law, the judges insisted.

“States have a duty to prevent significant harm to the environment by acting with due diligence and to use all means at their disposal to prevent activities carried out within their jurisdiction or control from causing significant harm to the climate system and other parts of the environment,” the opinion reads. 

Without mentioning the United States, which under President Donald Trump is withdrawing from the Paris Agreement for a second time, the ICJ’s Iwasawa said that not being a member of climate change treaties does not exempt a country from its duty to fight global warming.

“Customary obligations are the same for all states, and exist independently regardless of whether a state is a party to the climate change treaties,” he said. 

Countries also have a duty to cooperate on fighting climate change under international law, the court said. 

Clean environment a ‘human right’

Breaching these obligations “constitutes an internationally wrongful act entailing the responsibility of that state,” the judges said.

Such a breach may lead to legal consequences including, if a causal link can be established between a state’s climate inaction and damage from a climate disaster elsewhere, “full reparation to the injured states.” 

Establishing such a causal link is difficult, Iwasawa acknowledged, “but this does not mean that the identification of a causal link is impossible in the climate change context.” 

Reading out the opinion, Iwasawa offered a broad interpretation of countries’ legal duties in regards to climate change.

Notably, he said the ICJ considers limiting global warming to 1.5 degrees Celsius above pre-industrial levels the “primary goal” countries have agreed to under the Paris Agreement. The accord obliges countries to restrict the rise in temperatures to “well below” 2 C and ideally 1.5 C, but it’s the latter that become a symbol of global climate action. 

The world has already warmed to 1.3 C, and some scientists believe the world has missed the chance to meet the 1.5 C target. 

In general, the court said, global efforts to fight climate change are an essential part of human rights law. 

“The human right to a clean, healthy and sustainable environment is essential to the enjoyment of other human rights,” Iwasawa said. “Under international human rights law, states are required to take necessary measures in this regard.”