Kerry said a re-elected Trump could not stop investment and innovation in clean technology, but could frustrate it at a critical time when deep reductions to emissions are urgently needed.

"Acceleration of these markets is the name of the game. That is the key," the former US climate envoy said at a technology summit in London hosted by Microsoft co-founder Bill Gates.

That "urgency and the need to move faster in scale... would be hurt irreparably by the presence of President Trump", he added.

His remarks come ahead of a closely-watched debate between President Joe Biden and Trump, who pulled the United States out of the Paris climate accord and has cast doubt on the science of climate change.

Kerry said that the consequences of the world failing to limit temperature rises were playing out every day in disasters across the globe.

"I think we've got to remember what should what's driving us," he said. "This is life or death, literally."

Since stepping down as climate envoy in March, Kerry has been trying to drum up investment in clean energy and other solutions to drive down the emissions causing global warming.

The world needs trillions of dollars annually to make this happen "and no government has enough money to do this", he said.

"I believe the private sector is the entity that is going to solve this," he said.

Kerry told investors that Trump was "committed to blocking most of what you do" but that market forces would prevail in the end, even if frustrated.

"The marketplace is bigger than any one president or one country," Kerry told AFP.

"And the marketplace has made its decision to go in this direction because we have to (but) also because they think there's money to be made, and it's a better business model. So I'm confident we will continue no matter what."

Kerry 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 2015 Paris climate accord. Biden on taking office in 2021 appointed Kerry to a first cabinet-level role of special envoy on climate.