A historic decision by the UN's highest court paved the way for countries to sue each other over issues related to climate change. climate change, such as historic emissions of gases that contribute to global warming.

However, the judge at the International Court of Justice in The Hague, Netherlands, said Wednesday that it may be difficult to determine who is responsible for how much of this climate change.

The ruling is not binding, but experts say it could have far-reaching consequences.

It is a victory for countries most vulnerable to climate change, which came to the court frustrated by the lack of global progress in combating the problem.

“A legal milestone”

The unprecedented case before the International Court of Justice (ICJ) was the brainchild of a group of young law students from the Pacific islands, who are facing the effects of climate change firsthand.

One of those students, Siosiua Veikune, from Tonga, was in The Hague to hear the decision.

“I have no words. It’s very emotional. We are overwhelmed with emotions. It’s a victory that we can proudly take back to our communities,” she told BBC News.

“I will sleep more peacefully tonight. The ICJ recognized what we have experienced: our suffering, our resilience, and our right to a future,” said Flora Vano, from the island of Vanuatu, considered the most vulnerable country in the world to extreme weather events.

“This is a victory not only for us, but for all the affected communities who are fighting to be heard."

The ICJ is considered the highest court in the world and has global jurisdiction. Several lawyers told BBC News that the ruling could be used as early as next week, even in national courts.

Activists and lawyers hope the ruling will pave the way for compensation for countries that have historically burned the most fossil fuels and are therefore most responsible for global warming.

Many poorer countries had backed the case out of frustration that developed nations are failing to deliver on promises to tackle the growing problem.

But developed countries argued that existing climate agreements, including the landmark 2015 Paris accord, are sufficient and no further legal obligations should be imposed.

On Wednesday, the court rejected that argument.

Judge Iwasawa Yuji added that if countries do not develop the most ambitious plans possible to address climate change, it would constitute a breach of the promises they made in the Paris Agreement.

Iwasawa also noted that countries that have not signed the Paris Agreement — or wish to leave, such as the United States — are still bound by international law to protect the environment, including the climate system.

The court's opinion is advisory, but previous ICJ decisions have been followed by governments.

"The judgment is a legal landmark," said Joie Chowdhury, a lawyer at the Center for International Environmental Law (CIEL).

“With this historic and firm judgment, the International Court of Justice breaks with normality and reaffirms that those suffering the devastating effects of climate change have the right to reparation, including compensation,” he added.

What the decision entails

The court ruled that developing countries have the right to claim damages for the effects of climate change, such as the destruction of buildings and infrastructure.

And it added that, when it is not possible to restore part of the country, its government can claim compensation.

This could apply, for example, to a specific extreme weather event if it can be shown to have been caused by climate change, something the judge said will have to be determined on a case-by-case basis.

"This is a huge victory for climate-vulnerable states. It's a huge victory for Vanuatu, which led this case and is going to change the landscape of climate advocacy," said lawyer Stephanie Robinson, representing the Marshall Islands.

It's unclear how much each country would have to pay in damages if a claim were to succeed.

However,An earlier analysis published in Nature estimated that between 2000 and 2019, there were US$2.8 trillion in losses due to climate change, or US$16 million every hour.

During evidentiary hearings in December, the tribunal heard from dozens of Pacific Islanders who were displaced by rising sea levels caused by climate change.

The Marshall Islands highlighted that the cost of its adaptation to climate change amounts to US$9 billion.

“That’s US$9 billion that the Marshall Islands doesn’t have. Climate change is a problem they didn’t cause, but they are forced to consider relocating their capital,” he said. Robinson.

The court also ruled that governments are responsible for the climate impact of companies operating in their countries.

And it specifically stated that subsidizing the fossil fuel industry or approving new oil and gas licenses could constitute a breach of a country's obligations.

According to lawyers consulted by the BBC, developing countries are already considering filing new lawsuits against wealthier, higher-emitting nations based on the ICJ ruling, seeking compensation for their historic contributions to climate change.

If a country wants to bring a case to the ICJ for it to rule on compensation, it can only do so against countries that have accepted its jurisdiction, which neither the United States nor China include.

However, a claim can be filed with any court in the world, national or international, citing the ICJ ruling, explained Joie Chowdhury of CIEL.

A country can therefore choose to take its case not to the ICJ, but to a court to which those countries are legally bound, for example, the federal courts of the United States.

But the question remains whether the ICJ ruling will be respected.

“The ICJ” is an institution subject to geopolitics, which depends on states to abide by its rulings, as it does not have the power law enforcement,” said Harj Narulla, a climate lawyer who represented the Solomon Islands.

Asked about the decision, a White House spokesperson told BBC News:

“As always, President Trump and the entire administration are committed to putting America first and prioritizing the interests of ordinary Americans.”