BONN, Germany — The office of the official American delegation at the international climate talks here is almost always closed. A sign taped to the door informs the curious that entry is for authorized staff members only.
But there’s another group of Americans who are happy to be found. They are gathered in a nearly 27,000-square-foot inflatable tent adorned with American flags and red, white and blue signs proclaiming that states, cities and businesses are “still in” the Paris agreement, despite President Trump’s vow to leave it.
The alternate American pavilion, with its free espresso truck, tins of themed M&M’s and wireless internet that tells new users “the U.S. has not gone dark on climate action,” has rapidly become a hub of activity at the United Nations global warming negotiations taking place this week. On Saturday, a line of people waited in the rain to hear Michael R. Bloomberg, the former mayor of New York, Gov. Jerry Brown of California and a handful of United States senators, all Democrats, declare that much of America remains committed to reducing planet-warming carbon dioxide emissions.
“We’re in,” said Mr. Bloomberg, who put more than $1 million toward 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 dueling American delegations here mirror a larger division within the United States over climate change. Mr. Trump’s decision in June to withdraw from the Paris agreement was popular with his supporters. On Thursday, the State Department and the Interior Department sent high-level political officials to address a conference in Texas sponsored by the Heartland Institute, which rejects the scientific consensus that climate change is occurring and primarily caused by human emissions. Scott Pruitt, the administrator of the Environmental Protection Agency, sent a video message of support.
“We have tremendous natural resources, from coal to natural gas to oil, to generate electricity in a very cost-effective way,” Mr. Pruitt told the conference. “We should celebrate that and be good stewards.”
Yet seven in 10 Americans believe global warming is occurring, according to a Yale University survey, and more than 60 percent say they are at least “somewhat worried” about its effects.
“There’s a debate in the United States 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,” Governor Brown said 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 percent below 2005 levels by 2025.
Former Vice President Al Gore, a longtime champion of strong action on climate change, said Mr. Trump represented a minority view on the subject.
“President Trump does not speak for the country as a whole on the climate issue,” Mr. Gore said. “Of course he’s our president, of course he has the authority that any president has. But on this issue he is very much out of sync with the country as a whole.”
According to a new report from America’s Pledge, a group led by Mr. Bloomberg and Mr. Brown, if the institutions working to meet the Obama targets were a separate country, they would be the third-largest economy in the world after the United States and China. Even as the Trump administration plans to roll back federal climate change policies like the Clean Power Plan, the study found, falling clean technology prices, the low price of natural gas and local carbon-cutting efforts have already cut domestic greenhouse gas emissions by 11.5 percent between 2005 and 2015.
The official American 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 Monday when a team from the White House hosts a forum promoting fossil fuels and nuclear energy. Speakers will include executives from Peabody Energy, a coal company; NuScale Power, a nuclear engineering firm; and Tellurian, a liquefied natural gas exporter.
Christiana Figueres, a former United Nations climate envoy who spent her morning with the shadow American delegation, said the Trump administration was sending the wrong message to a conference aimed at decarbonizing the global economy.
“Coal is to be thanked for all of its hard work and it now deserves to be retired. It is of retirement age and needs to be put in the retirement home,” Ms. Figueres said.
Jim Lakely, a spokesman for the Heartland Institute, said he hoped United Nations climate delegates would also hear his group’s message. “Carbon dioxide is not a pollutant and it is not the driver of global warming,” he said. “So there is no moral case for restricting the use of fossil fuels, especially because that is vital to raising the quality and length of life of the world’s poorest people.”
Diplomats from other countries said they were glad to see governors, mayors and other Americans still committed to the Paris agreement making their presence felt. But they also said they weren’t sure which voice of American policy they should believe.
“Unfortunately there’s no connect between those processes,” said Dr. Ian Fry, lead negotiator for Tuvalu, a South Pacific island threatened by rising seas. “It’s just two worlds, unfortunately.”
An earlier version of this article referred incorrectly to a climate change advocacy group led by California Gov. Jerry Brown and Michael R. Bloomberg, the former New York mayor. It is America’s Pledge, not America’s Progress.