An international ocean court is expected to issue an advisory opinion on Tuesday on whether countries have a responsibility to reduce emissions and fight climate change - a judgement that could give legal leverage to future climate cases.
In its first-ever climate-related judgement, the International Tribunal for the Law of the Sea (ITLOS) in Hamburg, Germany, will decide specifically whether carbon emissions absorbed by ocean should be considered marine pollution, and whether nations are obligated to protect marine environments.
The court's opinion was requested by a group of island nations facing climate-driven sea-level rise.
"This is really an epic David and Goliath contest; it's the smallest of nations on Earth ... invoking the power of international law against the major polluter," said Payam Akhavan, the group's lead counsel in the proceedings, during a news briefing last week.
While the tribunal's opinion in the case will not be legally binding, it will be able to help guide countries in their climate policy and will be able to be used in other cases as legal precedent.
In the case hearings in September, China, the world's biggest carbon polluter, had challenged the islands' request, arguing that the tribunal does not have general authority to issue advisory opinions, saying its position was taken to avoid the fragmentation of international law.
"If ITLOS were to find that such an obligation exists, Beijing's response would most likely be to characterize this as falling outside of its proper scope of authority," Ryan Martinez Mitchell, law professor at the Chinese University of Hong Kong, told Reuters.
A decision that classifies greenhouse gas emissions as a form of pollution could focus attention on states' existing obligations to protect marine environments under U.N. Convention on the Law of the Sea, Akhavan said.
Some activists and environmental lawyers said they hoped for an opinion that pushes countries at the upcoming U.N. climate summit, COP29, in Baku, Azerbaijan, to set more ambitious climate targets.
"There will be clarity in terms of international law coming in and saying, well actually, legally, this is also a requirement," said lawyer Lea Main-Klingst for the legal charity ClientEarth.
The decision could also influence two upcoming legal opinions by the Inter-American Court on Human Rights, and the International Court of Justice - which are also considering states' climate obligations.
Already last month, the European Court of Human Rights issued a historic ruling in favour of plaintiffs who argued that Switzerland was violating their human rights by not doing enough to combat climate warming.
"This is about making international law work for us," said Vishal Prasad, campaign director for the group Pacific Island Students Fighting Climate Change. "It's about advancing the gaps that exist in the Paris agreement."
