Despite a strong rapport between the countries' veteran envoys, expectations for a breakthrough were low when John Kerry and Xie Zhenhua sat down for three days of talks in Beijing through Wednesday.

Kerry claimed progress, if mostly on getting relations back on track, but issues from U.S. politics to the diplomats' job prospects could make further advances difficult. China has not yet published an official reaction to the talks.

"We came here first of all to get back into sync," Kerry told reporters. "That is breaking ground: We were stopped, stymied for almost a year."

With relations at a low over national security issues, U.S. export bans on advanced technologies and China's state-led industrial policies, Washington has been trying to repair ties between the world's two biggest economies.

High-level U.S. visits to China had been halted due to Beijing's anger at a visit by U.S. then-House Speaker Nancy Pelosi in August 2022 to Taiwan, a self-governed island claimed by China. But in recent weeks, Secretary of State Antony Blinken and Treasury Secretary Janet Yellen visited ahead of Kerry, a former secretary of state and Democratic presidential candidate.

'AS GOOD AS IT CAN GET'

Washington and Beijing share a desire to accelerate the transition away from coal and abate methane, a potent greenhouse gas. Kerry said China agreed that a target to keep global temperatures rises within 1.5 Celsius of pre-industrial levels should remain "alive".

China has previous shown scepticism around the ability to achieve 1.5C, favouring the less stringent Paris target of 2C.

"I'm very comfortable we came out at a place where we had China ready and willing to work in an aggressive way - providing someone else or something else doesn't screw it up."

Li Shuo, climate adviser with environmental group Greenpeace in Beijing, said building more resilience into a still "fragile" diplomatic relationship was a crucial element in the talks.

"Overall, this is as good as it can get," said Li, who has been closely following China-U.S. climate diplomacy for more than a decade.

Kerry and Xie focussed on progress headed toward COP28, the annual U.N. climate summit in November.

Questions remain about the longer term, should political winds shift in the United States or the two diplomats leave their posts.

Kerry, powered by orange juice and ice cream sundaes during this week's marathon talks, turns 80 in December. Xie, 73, has been plagued by ill-health, limiting his trips overseas.

The U.S. envoy would not speculate on what would happen if he or Xie stepped down but acknowledged that U.S. politics, heating up before next year's presidential election, would make diplomacy harder.

Republicans who favour a harder line against China have criticised his trip.

NO 'PUSHING PEOPLE AROUND'

"We all understand the difficult situation for John Kerry," said Ma Jun, director of the Institute of Environment and Public Affairs, a Beijing environment group.

"He is passionate on climate, just like his counterpart, Special Envoy Xie," Ma said. "But in America, climate collaboration has been affected by local politics and that does make it quite difficult."

Disputes remain. Premier Li Qiang, meeting Kerry on Tuesday, raised the issue of finance, urging richer countries to make money available as soon as possible.

Top diplomat Wang Yi rejected Kerry's plea to ring-fence climate from broader bilateral disputes, saying climate "cannot be separated from the overall environment of Sino-U.S. relations".

The Communist Party-run People's Daily said last week the "oasis" of climate change cooperation could soon be a desert if the United States did not "meet China halfway" on issues like U.S. trade sanctions on solar panels.

But Kerry told reporters he was still optimistic that diplomacy could bring more rewards in the run-up to COP28 in Dubai.

"You don't come crashing in here and start pushing people around," he said. "You work through it. You talk. You build a relationship."