This treaty, ratified by 157 countries and which created the tribunal, imposes a "specific obligation to take all necessary measures to prevent, reduce and control marine pollution caused by anthropogenic emissions of greenhouse gases", said the tribunal based in Hamburg, Germany, in an opinion that was made public.

States will have to do everything to "reduce their emissions", "protect and preserve the marine environment from the impacts of climate change and ocean acidification" and "restore" ecosystems that have been destroyed, the tribunal explained.

The groundbreaking decision gives a new vision to the concept of "marine pollution" cited in the Convention, by including greenhouse gases.

The tribunal's opinion, which is advisory and not binding, will influence the interpretation of the treaty by national courts in the signatory countries, as well as by international justice.

Island States (Antigua and Barbuda, Bahamas, Niue, Palau, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Tuvalu and Vanuatu), threatened by rising sea levels, had appealed to this tribunal to force polluting countries to accelerate the fight against global warming.

Their leaders defended the case in the Hamburg court last September.

Signed in 1982, the United Nations Convention on the Law of the Sea requires signatory States to "take measures to prevent, reduce and control pollution of the marine environment and to protect and preserve that environment".

"Marine pollution" is defined as any "human introduction, directly or indirectly, of substances or energy into the marine environment (...) which has or is likely to have harmful effects".

According to this definition, "greenhouse gas emissions constitute marine pollution", the tribunal decided.

In recent years, there has been a proliferation of lawsuits against government inaction on climate, sometimes forcing policy decisions.

The International Court of Justice (ICJ) is also analysing a request from Vanuatu to clarify the "obligations" of States in relation to climate change.

In January 2023, Colombia and Chile requested an opinion from the Inter-American Court of Human Rights on the obligations of States to combat climate change under international human rights law.

In April of this year, the European Court of Human Rights heard three climate-related complaints, one of which was filed by a group of young Portuguese people. The Court partially upheld a complaint by elderly women against Switzerland.

Read Also: International Court of Justice hears South Africa and Israel this week (Portuguese version)