An international court says countries have an obligation to prevent harm from climate change and redress damage caused by greenhouse gas emissions.
Activists welcomed the non-binding advisory opinion issued by a 15-judge panel at the International Court of Justice in the Netherlands overnight as a step in the right direction.
The move to ask the world court to opine on the issue was initiated by Vanuatu University law students who argued the people of Pacific island countries were unjustly bearing the brunt of climate change compared to high-emitting economies.
"The degradation of the climate system and of other parts of the environment impairs the enjoyment of a range of rights protected by human rights law," presiding judge Yuji Iwasawa said, reading out the court's opinion.
The ICJ decision "confirms that states' obligations to protect human rights require taking measures to protect the climate system ... including mitigation and adaptation measures," judge Hilary Charlesworth, an Australian member of the court, said in a separate opinion.
"The ICJ's decision brings us closer to a world where governments can no longer turn a blind eye to their legal responsibilities," Vishal Prasad, director of the Pacific Islands Students Fighting Climate Change, said.
"It affirms a simple truth of climate justice: those who did the least to fuel this crisis deserve protection, reparations and a future".
The 133-page opinion was in response to two questions that the United Nations General Assembly put to the UN court: what are countries obliged to do under international law to protect the climate and environment from human-caused greenhouse gas emissions; and what are the legal consequences for governments when their acts, or lack of action, have significantly harmed the climate and environment?
Vanuatu Minister for Climate Change Adaptation Ralph Regenvanu called the deliberation a "very important course correction in this critically important time".
"For the first time in history, the ICJ has spoken directly about the biggest threat facing humanity," he said at The Hague.
Judge Iwasawa said the two questions "represent more than a legal problem: they concern an existential problem of planetary proportions that imperils all forms of life and the very health of our planet".
"International law, whose authority has been invoked by the General Assembly, has an important but ultimately limited role in resolving this problem," he said.
"A complete solution to this daunting, and self-inflicted, problem requires the contribution of all fields of human knowledge, whether law, science, economics or any other.
"Above all, a lasting and satisfactory solution requires human will and wisdom — at the individual, social and political levels — to change our habits, comforts and current way of life in order to secure a future for ourselves and those who are yet to come."
