Top Oceans Court Says Nations Must Reduce Greenhouse Gas Emissions

The world’s highest court dealing with the oceans issued a groundbreaking opinion on Tuesday that said excessive greenhouse gases were pollutants that could cause irreversible harm to the marine environment and must be cut back.

The advisory opinion by the court, the International Tribunal for the Law of the Sea, is not binding, but it stated that, legally, nations must take all necessary measures to reduce, control and prevent marine pollution caused by human-made greenhouse gas emissions.

The 21 judges on the tribunal were unanimous in their opinion, and experts say it could lead to more wide-ranging claims for damages against polluting nations.

The stance taken by the tribunal, which is sometimes called the Oceans Court, is also likely to affect how other international and national courts address the growing dangers posed by climate change.

The seas are vulnerable because the burning of fossil fuels releases greenhouse gases like carbon dioxide into the atmosphere, warming the world and contributing to a rise in sea levels by melting glaciers and ice sheets. Climate change also contributes to the heating and acidification of ocean waters, which affects marine life and the food chain, among other dangers.

The request for an advisory opinion was made by a group of small island nations that are already affected by rising sea levels as their coasts erode or become inhabitable and fresh water for drinking and planting crops turns saline. The court’s opinion applies to the more than 165 countries that ratified the United Nations Convention on the Law of the Sea, which includes large polluters such as China, Russia and India, but not the United States. (The Senate would not ratify the pact.)

The convention is the legal framework that covers the uses of the oceans and their resources, including the obligation to to protect the marine environment.

The opinion issued on Tuesday effectively expanded the definition of marine pollution to include greenhouse gases. The convention, which was negotiated in the 1970s, does not mention these emissions and their adverse effects on the world’s oceans, which are based on more recent science.

“We did not know how serious these emissions were in the 1970s,” said David Freestone, the co-author of a World Bank report last year on the legal dimension of sea-level rise who has followed the hearings and debates at the court. “At that time, people were concerned about acid rain.”

Scientists say that protecting the ocean’s role on the planet is overdue. Seas cover 70 percent of the earth’s surface and provide half of the world’s oxygen. They also absorb almost all of the excess heat generated by greenhouse gases and are warming faster than predicted, bringing more climatic changes.

Key questions addressed by the court included whether excessive greenhouse gases constitute “pollution of the marine environment” and, if so, whether countries can be held to account for that pollution. The judges said yes to both.

Leaders of the island nations that brought the case argue that existing climate accords have not made enough progress to prevent lasting damage to the oceans. They say that while they contribute only a small fraction of global emissions, they are already bearing the brunt of catastrophic effects of the changing climate.

“We got everything we asked for; we now have an authoritative definition of the obligations of states to avert irreversible harm,” said Payam Akhavan, the lead lawyer for the group of island nations, adding that the court “cited the best available science.”

The judges also appeared to side with the island nations that had long sought help in vain, saying that larger polluting nations had a greater responsibility than small and vulnerable states and should provide financial help and technical assistance to them.

Activists present in the court, which is in Hamburg, Germany, sent a volley of messages applauding the decision. “For the first time, an international court has recognized that the fate of two global commons — the oceans and the atmosphere — are intertwined and imperiled by the climate crisis,” Joie Chowdhury of the Center for International Environmental Law wrote.

Activists are increasingly taking on governments and energy companies for climate damages and have recently achieved rulings in their favor. In April, Europe’s highest human rights court unexpectedly sided with about 2,000 Swiss women over 64 years old who sued their government for not doing enough to prevent climate change. They said that their health was at risk during heat waves related to global warming.

Two other institutions, the International Court of Justice and the Inter-American Court of Human Rights, have also been asked for advisory opinions on the legal implications of climate change. Their opinions are due later.