The climate talks that concluded last December were a great success, but it will be decades before we can judge whether the Paris Agreement itself is ultimately successful. What can be said is that the accord provides a good foundation for meaningful progress on climate change, and represents a dramatic departure from the past 20 years of climate negotiations.I have long viewed the dichotomous distinction between Annex I and non–Annex I countries in the Kyoto Protocol as the major stumbling block to progress. The protocol included mandatory emissions-reduction obligations for developed countries, but none for developing countries. That made progress impossible, because significant growth in emissions since the protocol came into force in 2005 has been entirely in the large developing countries — China, India, Brazil, South Korea, South Africa, Mexico, and Indonesia.