Pacific Island communities once lived in harmony with the ocean, now their homes are threatened by rising sea levels. Caused in large part by warming global temperatures connected to the burning of fossil fuels for energy production and transport.

"Sea level rise is a huge problem for small island states with limited land for people to live on," Jule Schnakenberg, executive officer of World's Youth for Climate Justice, said, adding that it also limits people's access to fresh water to drink, grow food, and cook with.

Campaigners say it is human rights violations like these that motivated them to lobby governments into taking legal action. Those beginnings have culminated in a United Nations General Assembly decision to ask its highest court, the International Court of Justice (ICJ), for a legal opinion on the obligations of states concerning climate change.

Led by the Pacific Island of Vanuatu, 98 countries from all over the world and 12 international organizations are poised to give oral statements to the ICJ over the next two weeks. Judges at the court will issue an advisory opinion on the issue — and the legal consequences for governments that either fail to act or have taken action that significantly harms the environment.

"For several of us, this is a journey that has taken us five years and we recognize this milestone not as a goal, but rather as a checkpoint, a checkpoint because this is another step in the right direction in this fight for climate justice," said Siosiua Veikune, a campaigner with the Pacific Island Students Fighting Climate Change group.

Hiding behind the Paris Agreement

Whether drought, flooding or storms, the consequences of a hotter world are being felt all over the planet. But it is sea level rise that significantly impacts small island states like those in the Pacific. There, water levels are rising almost twice as fast as the global average, with increases of 10 to 15 centimeters (4 to 6 inches) in the western Pacific since 1993, according to the World Meteorological Organization.

UN assessments put current emissions-reduction targets promised by nations under the International Paris Agreement, on track for a global temperature  rise of up to 2.9 degrees Celsius. That is well above the accord's stated limit of 2 degrees with efforts to keep warming to 1.5 Celsius (2.7 Fahrenheit).

"There is such an unconscionable gap between where state policies need to be and where they are at and what justice and science demands is necessary [to be done] to avert climate catastrophe," Joie Chowdhury, senior attorney at the Center for International Environmental Law (CIEL), told DW.

Legal experts say the advisory opinion will clarify the obligations of states under already existing legislation and go beyond the scope of the Paris Agreement.

"These big polluters are trying to hide behind Paris, essentially saying that is all there is," Margaretha Wewerinke-Singh, who is representing Vanuatu in the ICJ climate hearings, told DW. She says the real question is whether the court will "confirm that there's more than Paris and that these other obligations also apply in parallel." 

The ICJ is one of three courts asked to issue an advisory opinion on the obligation of states concerning climate change. 

In May, the International Tribunal for the Law of the Sea was the first to issue its advisory opinion recognizing greenhouse gases as a form of marine pollution. It highlighted the obligations of states under the law of the sea as additional to those within the Paris Accord.

Following hearings earlier this year, the Inter-American Court of Human Rights is expected to deliver its opinion on the obligations of states to protect human rights concerning climate change before the ICJ issues its opinion.

Besides taking into account the two previous advisory opinions, experts say the ICJ will also consider other significant climate judgements, like the European Court of Human Rights ruling that Switzerland had violated the human rights of its citizens by missing past emissions reduction targets.

"We want to move towards kind of rights-based climate action so that people know they have a human right or many human rights, and that their states have to take all necessary measures [...]and do this on the basis of the best available science [...] and if states don't do that, you have a legal right to hold your government or companies accountable," said Schnakenberg.

A blueprint for climate litigation

Although advisory opinions from the ICJ are not legally binding, they do have political and legal significance.

In October, Ireland's government decided to unilaterally suspend trade with Israel on products originating from the occupied West Bank following an ICJ advisory opinion over the violation of Palestinian people's rights.

Legal experts say the ICJ advisory opinion on climate change could have similar political ramifications – particularly as countries prepare to submit new greenhouse gas emissions reduction targets in the run-up to the next United Nations climate summit in November 2025.

"That would probably be the ideal outcome, that the court just provides the course correction that is needed for the negotiations themselves, so then the ambition is increased," said Wewerinke-Singh.

If that is not the outcome, Chowdhury said the opinion could provide a "legal blueprint" for the international law that applies to climate change for potential litigation through domestic and international courts.

Currently, there are more than 2,000 climate cases taking place globally against states and companies.

"Of course, you're going to have to prove causality and it'll be dependent on a case-by-case basis, but what the court can do is lay out that the legal principle for remedy and reparations does exist under international law," added Chowdhury.

After years of fighting and finally making it to the ICJ hearings at the Hague, Schakenberg says she and the campaigners she is working with in the Pacific and around the world are hopeful.

"Throughout this campaign, we've always said that we are stubborn optimists, and I think we just have to believe that change is possible," she said.

Edited by: Tamsin Walker