Veteran US diplomat and politician John Kerry said Wednesday he planned to keep working to address climate change including by encouraging the private sector as he steps away from his envoy role.

Kerry said he believed the time was right to move on after the COP28 summit last month in Dubai, where the world for the first time as a whole called for an eventual transition away from fossil fuels responsible for global warming.

"I think we had a terrific outcome in Dubai, and I think it's a game-changer," he told AFP at the World Economic Forum in Davos, Switzerland.

"Now we have to make sure that the private sector people really step up," he said.

Kerry said he would "continue to work hard using other tools" on climate.

He said he would be supporting President Joe Biden's reelection campaign although he would not be taking a formal role.

Biden on taking office in 2021 appointed Kerry to a first cabinet-level role of special envoy on climate. It was a sign of the high priority his administration placed on the issue as the planet shatters warming records and endures increasing numbers of natural disasters.

After he took on the role, Kerry developed an unusually warm relationship with his Chinese counterpart Xie Zhenhua, who even brought his grandson to Dubai to meet the US negotiator.

Kerry welcomed Xie for a long weekend in California before the Dubai summit, culminating in a joint statement between the world's two largest carbon-emitting nations that helped form a basis for COP28.

Tensions have eased between the United States and China over the past year, but the level of friendliness is highly unusual between the two powers, which have sharp differences on a wide range of issues.

Xie also stepped down after COP28, saying he was retiring.

Kerry, who turned 80 during the Dubai summit, served as secretary of state and a senator and was the Democratic Party's unsuccessful candidate for president in 2004 against George W. Bush.

As the top diplomat under president Barack Obama, Kerry helped negotiate the breakthrough 2015 Paris climate accord from which Republican president Donald Trump -- who is seeking a comeback against Biden -- withdrew the United States.