Frustrated by the glacial global efforts to tackle climate change that are wrecking their homelands, 27 law students at the University of the South Pacific decided to, in their words, "get the world's biggest problem before the world's highest court".

Vishal Prasad, director of the campaign (Pacific Island Students Fighting Climate Change), admits to a mix of feelings at the culmination of a youth-led journey that started in 2019 on the other side of the world.

"Emotional, scared, nervous, anxious," Prasad told AFP outside the gates of the iconic Peace Palace in The Hague, where Wednesday's landmark ICJ ruling will be handed down.

"It's just a mix of all of that at the moment," said the 29-year-old Fijian, the driving force behind the civil society movement pushing for the court opinion.

The ICJ will lay out what responsibilities countries have to prevent climate change and whether penalties should be imposed on nations that have failed to do so.

But getting the top UN court to issue a so-called advisory opinion is no easy task -- the ICJ has delivered only 29 since its founding in 1946.

Only the UN General Assembly can request an advisory opinion from the 15 judges, which aims to clarify a particular point of international law.

Prasad's first task was to persuade Pacific Island leaders to join forces and flex their joint diplomatic muscle at the United Nations.

Led by Vanuatu, the Pacific Island Forum agreed at a conference in Fiji to take the issue to the UN General Assembly.

That's when Prasad's campaign went from regional to global and he moved to New York.

- 'Historic moment' -

Months of shuttle diplomacy followed, culminating in 2023 when the General Assembly agreed to request the ICJ opinion -- shifting the focus to The Hague.

During two weeks of hearings at the Peace Palace in December 2024, representatives from many Pacific Islands, including Prasad himself, addressed the judges, often for the first time in their country's history.

The vaulted Great Hall of Justice, used to hosting dry legal arguments from robed lawyers in wigs, saw a succession of Pacific Islanders, many in colourful traditional dress, deliver impassioned pleas for survival.

"Huge, huge moment. Historic moment," said Prasad of the hearings.

Prasad has seen first-hand the "heartbreaking" impact of climate change on his native Fiji and described the issue as "existential" for many Pacific Islanders.

Whole communities relocated, hospitals flooded at high tide; he said the scene from many low-lying islands was "like a horror movie".

"Climate change is not just an academic exercise... It's something you live day-to-day," he told AFP.

"It's an existential problem for young people in countries like Kiribati, in Tuvalu, in Marshall Islands. They're witnessing the effects of climate change every high tide," he added.

He believes the campaign's power comes from the fact that it is led by younger generations, who stand to lose the most from the changing climate.

"Before we can talk about anything else, we need to address the problem of climate change," he said.

"We need to protect our homes. We need to protect our identity and culture, because nothing exists if we're not able to save that."

He is hoping for an ICJ judgement that clarifies states' obligations on climate change and serves as a guideline for future global negotiations.

Prasad said the Pacific Island culture celebrates the concept of "wayfinding" -- "you need to correct your course if you are going wrong".

"And the ICJ... has a role similar to that, to course correct the world into meeting our targets, meeting our goals, so that we're on a path to a better future for all of us," he added.