Less than three years ago, he was chatting with fellow law students at the University of the South Pacific in Vanuatu about how they might someday help transform how the world tackles climate change.

Now, as world leaders descend upon New York for the UN General Assembly, Yeo and his fellow Pacific Islands students stand at the brink of ensuring that the world's biggest and smallest countries know their obligation to deal with climate change. To do that, they are closing in on their goal of successfully petitioning the world's highest court - the UN's International Court of Justice (ICJ).

The idea emerged as a law school conversation - what if they could persuade the ICJ to issue an advisory opinion on climate change? Such a thing had been tried before, by Palau’s government in 2012. But Yeo, who comes from the Solomon Islands, and the other students decided that a second effort could succeed if supported by leaders across the climate-vulnerable South Pacific.

And so, the students wrote letters - to island nation officials, legal scholars and environmental advocates - asking for support for their campaign. Now in New York, with dozens of his student colleagues, Yeo is giddy with the possibility of success.

“We never thought that it will ever reach this stage of the campaign,” he told Reuters. “It is truly an amazement to be here.”

An advisory opinion from the ICJ would not be legally binding in any jurisdiction, but it could clarify the international law around what responsibilities governments have to their citizens and other countries in relation to climate change. It could even define climate change as a human rights issue, similar to religious freedom or the right of education.

On Saturday, amid the bustle of midtown Manhattan, young Pacific Islands climate activists will launch a week of publicity promoting their effort, starting with a flotilla of boats lining up along the East River carrying placard-holding climate justice activists up to the United Nations, organizers said.

The activities will end with the government of Vanuatu and allies asking for the issue be put to a vote at U.N. General Assembly.

A successful vote, Yeo said, could result in the assembly referring the request to the ICJ in The Hague as soon as December.

It will be up to Vanuatu and supporting countries to decide exactly how to phrase the request, and what legal question it will ask the court to advise on. But Vanuatu's ambassador to the U.N., Odo Tevi, told Reuters the island nation was likely to focus on states' obligations to climate-vulnerable countries and to future generations.

"In the last five years, we have had two Category 5 cyclones, which wiped out almost 60% of our economy. So we think we also have the moral force to take up this cause," Tevi said.

With climate change accelerating the rise of sea levels, many low-lying island states and coastal communities face increasing risk from storms and flooding in coming years.

Spokesperson Bianca Beddoe of the 39-member Alliance of Small Island States, of which Vanuatu is a member, said the campaign "is a bold, important proposition ... and it will be important for consideration by all countries and the General Assembly.”

LEGAL AND MORAL AUTHORITY

Despite having no binding force, the ICJ's advisory opinions can still carry legal weight and moral authority, experts say. They are used often in diplomacy and in clarifying the law on complex international matters.

Such an opinion is increasingly needed, said ClientEarth lawyer Sam Hunter-Jones, as climate-related litigation ramps up worldwide. As of May, there were more than 2,000 climate-related court cases in play globally - more than double the number filed in 2015, according to the London School of Economics.

An opinion from the court could also bolster a key demand by poor nations for a special U.N. "Loss and Damage" fund to compensate damages already being suffered in climate-related disasters, such as lands being lost to sea level rise or destruction caused by supercharged storms. Or it could “spur international litigation between states, or against states regarding compensation,” Hunter-Jones said.

The students hope their campaign can also inject new life into global climate negotiations that often feel intractable, with wealthy nations resisting ambitious emissions-cutting pledges while also failing to deliver financing to help developing countries through the energy transition, said Fijian law student Vishal Prasad.

They plan to keep up the pressure leading up to the next U.N. climate summit - COP27 - to be held in Sharm el-Sheikh, Egypt, in November.

“Pacific Islanders, young people and all climate-vulnerable countries have so much to lose because of climate change,” Prasad said. And the world is “not moving as fast as we need to be” to prevent the worst of it.