US President Barack Obama and Chinese President Xi Jinping have entered their countries into the Paris climate agreement, pushing forward global efforts to curb climate change.
Obama and Xi handed over notification that their countries had joined the agreement to UN Secretary General Ban Ki-moon on the sidelines of Group of 20 Summit in Hanghzou, China on Saturday.
China's parliament ratified the Paris climate agreement earlier in the day, but no such action was necessary on the part of the US Congress.
The agreement, whose text was passed by nearly 200 countries in Paris last December, is the first universal action plan intended to mitigate the impacts of climate change and hold the rise in global average temperature to below 2C, compared to pre-industrial levels.
The ratification of the agreement is the third step in implementing the deal agreed in Paris last year and signed by the US, China and hundreds of other nations earlier this year.
The agreement will enter into force 30 days after 55 countries accounting for at least 55 per cent of global greenhouse emissions ratify it.
The move by the two top carbon dioxide emitters to ratify the treaty simultaneously is a major step forward in reaching that goal and continues co-operation between Washington and Beijing on climate that set the stage for the Paris agreement.
Before the US and Chinese move, 24 nations accounting for just over one per cent of global emissions had ratified the agreement.
White House climate adviser Brian Deese said that because the US and China together represent 40 per cent of global emissions it will put the world on a path to full implementation of the agreement.
"The signal of the two largest emitters taking this step together and taking it early should give confidence to the global community and other countries that they too can move quickly," Deese said.
The US and China also agreed on Saturday to work to reach a global agreement this year to phase out the global use of polluting hydrofluorocarbons and to support an international agreement to lower aviation emissions.
