The UN maritime court will on Monday hear a landmark case brought by a group of small island states seeking protection of the world's oceans from catastrophic climate change.
The nine island states have turned to the International Tribunal for the Law of the Sea to determine if carbon dioxide emissions absorbed by the oceans can be considered pollution, and if so, what obligations countries have to prevent it.
Ocean ecosystems create half the oxygen humans breathe and limit global warming by absorbing much of the carbon dioxide emitted by human activities.
But increasing emissions can warm and acidify seawaters, harming marine life.
The counties have pointed to the international treaty UNCLOS that binds countries to preventing pollution of the oceans.
The UN treaty defines pollution as the introduction by humans of "substances or energy into the marine environment" that leads to harm to marine life.
But it does not spell out carbon emissions as a specific pollutant, and the plaintiffs argue these emissions qualify.
"Entire marine and coastal ecosystems are dying in waters that are becoming warmer and more acidic. The science is clear and undisputed: these impacts are the result of climate change brought on by greenhouse gas emissions," said Tuvalu's Prime Minister Kausea Natano.
"We come here seeking urgent help, in the strong belief that international law is an essential mechanism for correcting the manifest injustice that our people are suffering as a result of climate change."
- Marine heatwave -
The push for climate justice won a big boost when the UN General Assembly in March adopted a resolution calling on the International Court of Justice to lay out nations' obligations on protecting Earth's climate and the legal consequences they face if they fail to do so.
The move at the UN had been led by Vanuatu, which also counts among the plaintiffs in Monday's case in Hamburg, Germany.
Small islands like Vanuatu are particularly exposed to the impact of global warming, with seawater rises threatening to submerge entire countries.
"Without rapid and ambitious action, climate change may prevent my children and grandchildren from living on the island of their ancestors, the island that we call home. We cannot remain silent in the face of such injustice," said the Prime Minister of Antigua and Barbuda, Gaston Browne.
"We have come before this Tribunal in the belief that international law must play a central role in addressing the catastrophe that we witness unfolding before our eyes," he added.
Across the two-thirds of the planet covered by seas, nearly 60 percent of ocean surface waters experienced at least one marine heatwave in 2022, according to the annual State of the Climate report led by scientists from the US National Oceanic and Atmospheric Administration.
This is 50 percent more than pre-industrial levels and "the highest in the modern atmospheric record and in paleoclimate records dating back as far as 800,000 years", the report published this month noted.
The world's oceans also set a new temperature record in August. Average sea surface temperatures reached an unprecedented 21 degrees Celsius (69.8 degrees Fahrenheit) for over a week, according to the EU's Copernicus Climate Change Service, after months of unusually high temperatures.
Other plaintiffs in the ITLOS case include The Bahamas, Niue, Palau, St Kitts and Nevis, St Lucia as well as St Vincent and the Grenadines.
Thirty-four other state parties will also participate in the court hearing, with sessions scheduled through to September 25.