Convincing the US to remain in the Paris Agreement is in the mutual interest of China and the US, he said. “There may be those in China who feel it would be easier in ongoing negotiations if the US were not there, but that would be very short-sighted,” Stern said.

On May 26, Trump will make his G7 debut with national leaders from seven major advanced economies, including UK Prime Minister Theresa May, German Chancellor Angela Merkel and newly elected French President Emmanuel Macron, all of whom have committed to a “swift and successful implementation” of the Paris Agreement.

In a phone call with Macron on May 9, Xi vowed to stick to the accord. China and France should “protect the global governance achievements contained within the Paris Agreement on climate change,” Xi told Macron, according to the Chinese foreign ministry. China is not a member of the Group of Seven.

Trump accused China in a November 2012 tweet of perpetuating what he called the climate change hoax. “The concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive,” Trump said on Twitter. In January 2016, as the US presidential race heated up, Trump backed off from this claim, saying it was a “joke”.

Trump’s aides, including his daughter, Ivanka, and son-in-law Jared Kushner, have been divided over whether to abandon the Paris Agreement; the debate among them became intense at the end of April. Another option under discussion is lowering the US’ national determined contribution target under zthe climate agreement.

For US Secretary of State Rex Tillerson, the bottom line is keeping the US in the UN climate talks. In his Senate hearing in January, Tillerson said: “I think it’s 190 countries have signed on. We’re better served by being at that table than by leaving that table.”

Between Xi and Trump, there are no official public records of direct phone calls mentioning the Paris Agreement since the pair’s meeting in Florida in early April. Climate change was not on the public agenda at the time. A representative of China’s National Development and Reform Commission, the government body in charge of climate negotiations, could not be reached for comment.

Climate change had been a pillar of China-US bilateral relations under the administration of former US President Barack Obama. Stern recalled that his counterpart, Xie Zhenhua, China’s special envoy for climate change, “became one of my very good friends during years of working together, sometimes battling each other, but we were always very close”.

When the UN failed to reach a landmark climate deal eight years ago in Copenhagen, Stern talked to Xie about the notion that even though climate change had been “an area of stress and tension” between the US and China, historically, the two nations “had a real opportunity to make this a positive pillar for our relations,” Stern said. “And (Xie) thought the same thing.”

China and the US have experienced climate-negotiation drama together. During the UN climate talks in Copenhagen in 2009, Obama and then-Secretary of State Hillary Clinton reportedly forced themselves into a room where then-Chinese premier Wen Jiabao was holding a secret meeting with leaders from India, Brazil and South Africa.

China has expressed its desire to take the lead in the battle against global climate change. Xie said China is capable of taking a leadership role in the campaign as well as being open toward collaborating with all countries to achieve necessary economic restructuring, reiterating remarks he made earlier this year.

No country can formally seek to withdraw from the Paris Agreement until October 2019. If one does decide to leave, there is a one-year waiting period for the withdrawal to become official. “But if the President says we are leaving, then as a practical matter, it takes effect immediately,” Stern said.