President Obama arrived in China today to attend the G-20 summit of major world leaders.
Obama and his Chinese counterpart Xi Jinping handed ratification documents to United Nations chief Ban Ki-moon, who said he was now optimistic the agreement will be in force by the end of this year. For example, the European Union has a "national determined contribution" of cutting emissions 40 percent by 2030 on 1990 levels, and the U.S.by up to 28 percent by 2025 compared with 2005.
"This is not a fight that any one country no matter how powerful can take alone", Mr Obama said alongside Mr Xi just hours after touching down in China on Saturday afternoon.
WWF-US senior vice president for climate and energy Lou Leonard said the move will spur high hopes for the United Nations special event planned for 21 September in NY aimed at securing the early entry into force of the Paris Agreement.
The global economic recovery remained weak and G20 countries should take steps to revive trade and investment, Xi said, pointing to challenges including the refugee crisis, climate change and terrorism.
"The general accepted wisdom was that it would take several years, perhaps a couple of years, for the Paris agreement to enter into force", Brian Deese, a senior adviser to the president who focuses on environmental issues, told reporters Friday.
For the agreement to come into force, at least 55 countries representing 55% of the world's climate emissions must ratify the deal to drive down greenhouse gases.
China had said in April that it would ratify the Paris Agreement, negotiated by representatives of 195 nations in Paris past year, before its hosting of the G-20 summit.
China represents just over 20 percent of global emissions while the United States accounting for 17.9 percent, Russian Federation 7.5 percent and India 4.1 percent.
Obama is expected to meet with China's President Xi Jinping Saturday afternoon.
The Paris deal is the world's first climate arrangement that is comprehensive. They hailed their new era of climate cooperation as the best chance for saving the planet.
China and the United States - responsible for around 40 percent of the world's carbon emissions - today jointly ratified the Paris climate change deal that aims to significantly reduce global emissions, giving hopes that the landmark accord may come into effect by the end of this year.
Beyond economics, there may be friction over territorial disputes in the South China Sea and a U.S.
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. A Chinese official kept reporters and some top White House aides away from the president, prompting a USA official to intervene.
With the agreement, China has committed to, compared to 2005 levels, cut carbon emissions by 60 to 65 percent per unit of GDP by 2030, and source 20 percent of its energy from renewable energies like hydro- and wind power, state-news agency Xinhua said.