The International Court of Justice (ICJ) has been tasked with crafting a so-called advisory opinion on countries' obligations to prevent climate change and the consequences for polluters whose emissions have harmed the planet.
Experts say this is the most significant in a string of recent rulings on climate change in international law, with major potential repercussions for states and firms around the world.
Climate-vulnerable countries and campaign groups hope it will have far-reaching legal consequences in the fight against climate change, unifying existing law, shaping national and international legislation, and impacting current court cases.
"It will be the compass the world needs to course correct," said Vishal Prasad, director of the Pacific Islands Students Fighting Climate Change.
"It will give new strength to climate litigation, inspire more ambitious national policies and guide states toward decisions that uphold their legal duties to protect both people and planet," said Prasad.
But some critics argue the ruling will be toothless, as ICJ advisory opinions are not binding and major polluters can choose simply to ignore it.
- 'Acts and omissions' -
The UN, pushed by tiny island state Vanuatu, asked the court to answer two questions.
First, what obligations do states have under international law to protect the Earth's climate from polluting greenhouse gas emissions?
Second, what are the legal consequences for states which "by their acts and omissions have caused significant harm to the climate system and other parts of the environment?"
The second question was explicitly linked to the damage that climate change is causing to small, more vulnerable, countries and their populations.
This applies to countries facing increasingly damaging weather disasters and especially to island nations under threat from rising sea levels like those in the Pacific Ocean.
- 'David Vs Goliath' -
In what was termed a "David versus Goliath" battle, advanced economies and developing nations clashed at the ICJ during December hearings on the case.
The iconic Peace Palace in the Hague, the seat of the ICJ, played host to more than 100 oral submissions -- the largest number ever, many from tiny states making their first appearance.
"This may well be the most consequential case in the history of humanity," said Vanuatu's representative Ralph Regenvanu, opening the two weeks of hearings.
"The outcome of these proceedings will reverberate across generations, determining the fate of nations like mine and the future of our planet," he told the 15-judge panel.
Major polluters argued the UN Framework Convention on Climate Change (UNFCCC) was sufficient and new guidelines on countries' obligations were not necessary.
US representative Margaret Taylor said this framework was "the most current expression of states' consent to be bound by international law in respect of climate change".
Taylor urged the court "to ensure its opinion preserves and promotes the centrality of this regime".
Meanwhile, the speaker from India was even more explicit.
"The court should avoid the creation of any new or additional obligations beyond those already existing under the climate change regime," said Luther Rangreji.
The United States under President Donald Trump has since pulled funding for the UNFCCC and withdrawn from its landmark pact, the Paris climate agreement.
- 'Watery graves' -
But smaller states said this framework was inadequate to mitigate climate change's devastating effects.
"As seas rise faster than predicted, these states must stop.
"This court must not permit them to condemn our lands and our people to watery graves," said John Silk from the Marshall Islands.
After bitterly fought UN climate talks in Azerbaijan in November, wealthy countries agreed to provide at least $300 billion a year by 2035 to help developing nations transition to clean energy and prepare for an increase in extreme weather.
The vulnerable nations argued this is simply not enough and urged the ICJ to push for more.
"This is a crisis of survival. It is also a crisis of equity," said Fiji's representative Luke Daunivalu.
"Our people... are unfairly and unjustly footing the bill for a crisis they did not create.
"They look to this court for clarity, for decisiveness and justice."
World's major courts take growing role in climate fight
Paris (AFP) July 21, 2025 -
The world's top court is poised to tell governments what their legal obligations are to tackle global warming, and possibly outline consequences for polluters that cause climate harm to vulnerable countries.
Wednesday's highly anticipated advisory opinion by the International Court of Justice comes in the wake of landmark international decisions that experts say together have the potential to significantly shape climate action.
- How has climate litigation evolved? -
Andrew Raine, deputy director of the UN Environment Programme's law division, said frustration over the pace of climate action had spurred people, organisations and countries to turn to the courts.
"When political systems fall short, the law is increasingly seen as a tool for driving ambition and enforcing commitments that have been made," he told AFP.
These have been bolstered by increasingly precise and detailed climate science, including from the UN's IPCC climate expert panel.
Almost 3,000 climate cases have been filed up to the end of 2024, in nearly 60 countries, according to the Grantham Research Institute, using data compiled by the Sabin Center for Climate Change Law.
While not all have been successful -- and some have tried to slow climate progress -- there have been notable cases in recent years that have pushed states to do more.
Urgenda, an environmental organisation in the Netherlands, notched a win at the Dutch Supreme Court in 2019, with justices ordering the government to reduce its greenhouse gas emissions by 25 percent by the end of the following year.
And in 2021, the German Constitutional Court found that the government's failure to sufficiently cut planet-heating pollution placed an unacceptable burden on future generations.
Raine said that litigation was increasingly crossing borders, with 24 cases brought before international or regional courts, tribunals or other bodies.
"This marks a turning point and it reflects the transboundary and shared nature of the climate crisis," he said.
- Why have recent cases been deemed historic? -
Two in particular have been hailed as watershed moments that will help shape how courts, governments and businesses understand and act on their climate responsibilities.
Last year, an advisory opinion by the International Tribunal for the Law of the Sea said carbon emissions can be considered a marine pollutant and that countries have a legal duty to take measures to reduce their effects on oceans.
The tribunal made clear that the work of defining countries' obligations is not limited to the Paris climate agreement or the UN body that runs climate change negotiations.
Major polluters have argued that the UN framework is sufficient and against courts taking climate decisions.
Another major advisory opinion was issued this month, with the Inter-American Court of Human Rights reaffirming the right to a healthy climate system and acknowledging the rights of nature.
But perhaps the court's most profound statement was to place protection against irreversible climate harms on the same level as international prohibitions on genocide and torture, said Cesar Rodriguez-Garavito, Professor of Law and Director of the Climate Law Accelerator at New York University.
The court said "massive and serious harm to the climate system through emissions, through deforestation and so on, is absolutely forbidden by international law," he said.
In his view this made it the strongest statement yet by any international court on states' duty to avoid causing severe ecological destruction.
All eyes are now on the ICJ.
- What could be the impact? -
Vanuatu, one of many low-lying islands threatened by sea level rise, has asked the ICJ to give its opinion on states' obligations to reduce emissions.
But the potentially more controversial request is what -- if any -- legal consequences there might be for major polluters who cause severe climate damages.
"These are questions of global justice," said Rodriguez-Garavito, potentially touching on contentious issues of "reparations for climate harms" to those least responsible for emissions.
While advisory opinions like the ICJ are not legally enforceable, Raine said they carry significant weight.
"They clarify how international law applies to the climate crisis, and that has ripple effects across national courts, legislative processes and public debates," he said.
"It doesn't force states to act, but it shows them where the law stands and where they should be headed."
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