China and the United States have ratified the Paris climate change agreement, in a move campaigners hope is a step forward in the world's fight against global warming.
China and the United States on Saturday announced they would formally ratify the Paris climate change agreement to cut climate-warming emissions.
The two countries are together responsible for 38 percent of the world's carbon emissions, which are the driving force behind climate change.
They are followed by Russia at 7.5 percent and India at 4.1 percent.
The Paris agreement was adopted last December by all 195 members of the United Nations Framework Convention on Climate Change and the European Union.
It is aimed at dealing with greenhouse gas emission mitigation, adaptation and finance starting in the year 2020.
The deal will enter into force fully only if at least 55 countries representing at least 55 percent of global emissions ratify it. The two countries' announcement is vital as it might turn the Paris deal into reality by encouraging other countries to follow suit.
Bill Hare, chief executive of Climate Analytics, stated, "We expect a surge of ratifications around the UN Climate week later in September."
Before the US and China announced the decision, 23 nations had ratified the agreement, accounting for just over 1 percent of emissions.
#COP21 US and China ratifying Paris Agreement. Two biggest emitters delivering. Important step forward!— Carole Dieschbourg (@DieschbourgC) September 3, 2016
The announcement came as heads of state of the 20 biggest economies, or G20, arrived for a summit in the Chinese city of Hangzhou.
The joint ratification of the Paris accords is a major diplomatic achievement for US President Barack Obama, who ends his term in January.
According to Li Shuo, a climate adviser with Greenpeace, both China and the US are determined to put the treaty into force as soon as possible in order to avoid the risk that any new Republican administration would reject it.
Democratic presidential candidate Hillary Clinton is a strong supporter of the pact, but her Republican counterpart Donald Trump has dismissed man-made climate change as a hoax and says he will abandon the Paris agreement if elected.
The US Republican Party Platform has questioned the legality of the executive order used to ratify the Paris deal, saying it will need the consent of the Senate before it becomes binding.
On the other hand, Obama hailed the move, which he described as "pivotal."
"Just as I believe the Paris agreement will ultimately prove to be a turning point for our planet, I believe that history will judge today's efforts as pivotal," Obama said after he and his Chinese counterpart Xi Jinping handed the ratified documents to UN Secretary-General Ban Ki-moon.
"We have a saying in America that you need to put your money where your mouth is. And when it comes to combating climate change, that's what we're doing. Both the United States and China, we're leading by example," the president said.
Likewise, Xi said the two countries' efforts "speak to the shared ambition and resolve of China and the United States in addressing global issues."
"I have said many times that green mountains and clear water are as good as mountains of gold and silver. To protect the environment is to protect productivity and to improve the environment is to boost productivity," Xi said.
"We will unwaveringly pursue sustainable development and stay committed to green, low-carbon and circular development and to China's fundamental policy of conserving resources and protecting the environment."