China ratified the Paris climate change accord on Saturday, with the US expected to do so later in a joint stand against global warming by the world?s two biggest polluters.
The accord sets ambitious goals for capping global warming and funnelling trillions of dollars to poor countries facing an onslaught of damage as a result of climate change.
It will come into effect 30 days after at least 55 countries, accounting for 55 percent of global greenhouse gas emissions, have ratified it.
China is responsible for around a quarter of the world?s emissions, with the US in second place on more than 15 percent, so their participation is crucial.
China?s legislature, the National People?s Congress, voted to adopt ?the proposal to review and ratify the Paris Agreement?, the official Xinhua news agency said.
US President Barack Obama is due to arrive in China later Saturday for a G20 summit in the eastern city of Hangzhou, and is expected to announce the formal joining of the accord with President Xi Jinping.
Campaigners welcomed the move.
?China and the US, the two largest developing and developed country economies and emitters, joining the Paris Agreement shows that the global community can come together to address the threat of climate change,? said Alvin Lin of the US-based Natural Resources Defense Council.
?Both countries are transforming their economies to grow through clean energy rather than fossil fuels, so their citizens can benefit from a cleaner environment and be competitive in the green economy,? he told AFP.
? Pressure on G20 leaders ?
The two giants are expected to use the summit, a gathering of the world?s leading developed and emerging economies, to pressure others to do so.
?Xi and Obama should seize the opportunity to lead the world?s 20 wealthiest nations by joining and building on the Paris agreement,? said Greenpeace East Asia?s senior climate policy adviser Li Shuo.
It is time for the Paris accord to ?move from agreement to action?, he added. ?Political ambition must keep up with rising sea levels faced by vulnerable communities around the world.?
The Paris pact calls for capping global warming at well below two degrees Celsius (3.6 degrees Fahrenheit), and 1.5 C (2.7 F) if possible, compared with pre-industrial levels.
Until Saturday only 24 of the 180 signatories had ratified it, including France and many island states threatened by rising sea levels but who only produce a tiny proportion of the world?s emissions.
For China, ratifying the agreement fits with Beijing?s domestic political agenda of being seen to make efforts to clean up the environment, after years of breakneck industrial development led to soaring air, water and ground pollution.
The scourge is estimated to have caused hundreds of thousands of early deaths, and is the source of mounting public anger.
Under the Paris accord, Xinhua said, China will have to cut its carbon emissions per unit of GDP by 60-65 percent from 2005 levels by 2030 and increase non-fossil fuel sources in primary energy consumption to about 20 percent.
Neither of those requirements implies a commitment to cut absolute levels of emissions, although China is also obliged to have them peak by 2030.
During the negotiations over the Paris deal Beijing stressed the concept of ?differentiated responsibilities? ? the idea that developed countries should shoulder the lion?s share of the burden as they have polluted most since the Industrial Revolution.
China previously committed to its emissions peaking ?around 2030?, a declaration made on an earlier visit by Obama, when he announced a target for the US to cut its own emissions 26-28 percent below 2005 levels by 2025.