The world’s top greenhouse gas emitters denied they had any obligations beyond the UN framework convention on climate change (UNFCCC) and the 2015 Paris agreement. The court resoundingly rejected that argument, saying a range of other treaties applied, including the UN convention on the law of the sea, the Vienna convention for the protection of the ozone layer, the Montreal protocol, the convention on biological diversity and the UN convention to combat desertification.

Customary international law also applied, it said, including principles of sustainable development, common but differentiated responsibilities, equity, intergenerational equity and the precautionary principle. States also had a duty to work together to protect the climate, the court said