In addition to the small island states, countries including Germany, France, Saudi Arabia and Australia will speak at hearing sessions scheduled until Sept. 25.
The tribunal will then issue an advisory opinion, which is not legally binding, but offers an authoritative statement on legal matters that could guide countries as they craft climate protection law.
"Today is indeed a historic day ... As we seek to get answers to a couple of questions to determine the obligations of states parties," Antigua's Gaston Browne said at a news conference following the hour-long hearing.
environment under the United Nations convention on the Law of the Sea, including from greenhouse gas emissions.
"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," said Tuvalu's Natano at the hearing.
Excessive carbon pollution results in damage to the oceans, including coral bleaching and acidification. Low-lying island states like Tuvalu and Vanuatu are also at risk of becoming submerged by water by the end of the century due to slow-onset climate impacts.
"Over 30 years, we have been pleading with the large emitters of greenhouse gases to reduce emissions. But they have not heeded our calls," Browne said, calling for immediate action to reduce global temperatures.
He said the tribunal process was a complementary pathway to the diplomatic actions the island states were taking at the U.N. summits which have yielded slow progress.
"These hearings represent a significant step toward defining the climate-related obligations of states under the U.N. Convention on the Law of the Sea," said Pepe Clarke, oceans practice leader at World Wildlife Fund.
Small island nations have also sought legal clarity on nations' climate obligations in other courts. Vanuatu led a campaign to ask the International Court of Justice (ICJ) to issue an advisory opinion on countries' obligations to address climate change.
The U.N. General Assembly in March voted to refer the case to the ICJ, which will issue an opinion in 2024.