Dhaka, Aug. 15 -- Although the International Court of Justice turned 80 this year, there is a sense in which it has never felt younger. In a David-versus-Goliath moment, the tiny Pacific Island state of Vanuatu recently changed international law forever by bringing the world's most important issue before its highest court. The result is an ICJ advisory opinion on "the legal obligations of states in respect of climate change," as requested - at Vanuatu's urging - by the United Nations General Assembly (with 132 states co-sponsoring the resolution).

The questions posed to the ICJ were as simple as they were seismic: What obligations, under international law, do states have to tackle climate change? And what are the legal consequences if th...