United States President Barack Obama and Chinese President Xi Jinping formally joined the Paris climate agreement yesterday at a ceremony in the Chinese city of Hangzhou.
The move by the leaders of the world's two biggest polluters is a major step forward for the deal. Together, China and the US generate nearly 40 per cent of global carbon emissions, not far from the threshold of 55 per cent required for the pact to take effect.
United Nations chief Ban Ki Moon said he was optimistic the agreement will be in force by the end of this year.
