BONN (Germany) • The office of the official US delegation at the international climate talks here is almost always closed. A sign taped to the door informs the curious that entry is for authorised staff only.

But there is another group of Americans who are happy to be found. They are gathered in a nearly 27,000 sq ft inflatable tent adorned with US flags and red, white and blue signs proclaiming that states, cities and businesses are "still in" the Paris agreement despite President Donald Trump's vow to leave it.

The alternate United States pavilion, with its free espresso truck, tins of themed M&Ms and wireless Internet that tells new users "the US has not gone dark on climate action", has rapidly become a hub of activity at the ongoing United Nations global warming negotiations.

Last Saturday, a line of people waited in the rain to hear former New York mayor Michael Bloomberg, California Governor Jerry Brown and a handful of US senators, all Democrats, declare that much of the US remains committed to reducing planet-warming carbon dioxide emissions.

"We're in," said Mr Bloomberg, who put more than US$1 million (S$1.4 million) towards funding the pavilion, according to his office. "Just because the federal government has chosen not to participate," he added in an interview, "the American public represented by its elected officials at other levels, by corporations, by universities, we understand that there's a problem, and we have to help solve that problem if we're going to have a future in this world."

The duelling US delegations mirror a larger division within the US over climate change. Mr Trump's decision in June to withdraw from the Paris agreement was popular with his supporters.

Yet seven in 10 Americans believe global warming is occurring, according to a Yale University survey, and more than 60 per cent say they are at least "somewhat worried" about its effects.

"There's a debate in the US between the denialists, who pooh-pooh any thought about climate change and the catastrophic dangers it portends, and those who agree with the scientific academies of every country in the world that we're facing an existential threat and we have to do something about it," Mr Brown said last Saturday.

He and Mr Bloomberg announced that the states, cities and businesses that had pledged to abide by the Paris accord were on track to meet the Obama administration pledge to cut emissions at least 26 per cent below 2005 levels by 2025.

The official US negotiating team for now is laying low.

Career State Department officials are managing the technical negotiations, speaking up on issues like demanding more transparency from developing countries on their progress cutting emissions.

The Trump administration's true debut will come when a team from the White House hosts a forum promoting fossil fuels and nuclear energy today.

NYTIMES