The climate deal reached in Paris is "the best chance we have to save the one planet we have", US President Barack Obama has said.
He said it could be a "turning point" towards a low-carbon future.
China, the world's biggest polluter, also hailed the deal, as did India. But some campaigners said it did not go far enough to protect the planet.
The Paris pact aims to curb global warming to less than 2C (3.6F) by the end of the century.
Nearly 200 countries took part in tense negotiations in the French capital over two weeks, striking the first deal to commit all nations to cut emissions.