THE MOST far-reaching, and controversial, ruling ever issued by the world’s top court—that failing to protect the climate from greenhouse-gas emissions could be deemed an “internationally wrongful act” by a country—had the humblest of beginnings. In 2019, a group of law students at the University of the South Pacific, in Fiji, were set an assignment that snowballed. Asked to think of ways to reduce the inequalities of climate change, they began campaigning to get the International Court of Justice (ICJ) in The Hague to consider what obligations states had to tackle climate change under international law, and what consequences they might face if they failed to meet them. By 2023, at the urging of politicians from Vanuatu and other small island states, the ICJ had agreed to give its legal opinion on the matter at the formal request of the United Nations General Assembly.