Gov. Jerry Brown led a group of U.S. political and business leaders visiting Germany this week to make a sales pitch to the rest of the world: that most Americans don’t support President Trump’s agenda on climate change — or lack thereof.

For the first time since Trump vowed to pull out of the 2015 Paris climate agreement, the international community is meeting to discuss how to go about cutting greenhouse gas emissions, an effort that’s only become harder with America’s new outsider status. Even Syria, the other holdout on the climate deal, revealed last week it’s now on board.

But over the course of a week and a half and four countries, with a chartered jet and a handful of staffers, Brown has sought to reassure the more than 190 nations participating in this month’s U.N. climate summit that, even without the White House, American cities and states can make progress fighting global warming.

“We are here to forge partnerships,” Brown said in a telephone interview Monday from Bonn, Germany. “People are very glad America is represented. It’s not just California, but Virginia, Washington, Oregon … There’s just a plethora of actors that are here and that, I think, is encouraging to other countries and other regions.”

While Brown and other big-name American climate advocates, including former Vice President Al Gore and ex-New York Mayor Michael Bloomberg, don’t officially speak for the United States, they and dozens of others from the U.S. occupy a massive inflatable tent with a stage and seating outside the conference, decorated by American flags and the hashtag “#WeAreStillIn.” Witnesses described long lines to get in over the weekend.

The group is in stark contrast to the official U.S. delegation, a panel of career government workers that has kept a relatively low profile. The faction gave one of its few presentations Monday, focusing on the benefits of clean coal and other fossil fuels.

Meanwhile, Brown has extolled the virtues of a green economy at more than a dozen events, heralding the success of a coalition of 14 states, including California, that’s on track to meet a goal of reducing greenhouse gas emissions by at least 26 percent by 2025 from 2005 levels. That was the target set by the Obama administration when the U.S. was committed to the Paris accord.

While the coalition is unlikely to carry the rest of the country past the goal line, a report unveiled last week by an alliance of U.S. cities, states and businesses, known as America’s Pledge, underscored the significance of the local effort. If the U.S. institutions that are committed to cutting greenhouse gas emissions were a sovereign nation, they’d be the third largest economy in the world.

Brown, who has little more than a year left in his final term in office, has pushed hard during his governorship for stricter California climate policies, while lobbying other nations and states to do the same.

His current trip has taken him to Vatican City, Belgium, Norway and finally Germany, where he said the mission was as important as anything he’s done.

“We’re talking about real destruction, not some political sidebar,” he said. “The fact that you have a Republican Party in denial and a president that has invented this notion that climate change is a hoax, it’s so far-fetched. It’s hard to believe that a human being said that, but Donald Trump did.”

At a meeting of the European Parliament last week, Brown went as far as calling for California and the European Union to consider linking their cap-and-trade programs. Such a partnership, while logistically challenging, could create a carbon trading market that severely limits the greenhouse gas emissions of industry on a global scale.

Perhaps Brown’s most notable contribution during his travels, observers say, is highlighting what can be done at the local and regional level — without federal support — to make emissions cuts while being economically viable. California is home to dozens of climate-fighting programs, from renewable energy mandates to clean fuel standards to green building codes.

Lou Leonard, senior vice president for climate change and energy at the World Wildlife Fund, said not having the U.S as a signatory to the Paris accord is disappointing, but added that the work of Brown and others outside Washington goes a long way.

“What’s been achieved so far has been achieved by the work at the city and state level,” Leonard said. “There’s reason to believe that this sub-national approach to delivering on the Paris agreement can work.”

But not everyone thinks Brown is doing as much as he can. During a Saturday speech in Bonn, the governor was heckled by a group of protestors concerned that he’s done too little to restrict oil drilling and fracking at home.

Brown acknowledged Monday he has to be reasonable in his approach to cutting greenhouse gas emissions, especially in a state with 32 million vehicles that are largely dependent on fossil fuels.

“I agree we have to get off oil,” he said. “But just to put up a sign and interrupt a climate meeting and toss out a few jingles, that doesn’t shed any light or serve any cause.”

This week, the goal of keeping worldwide temperatures from increasing more than 2 degrees Celsius, as laid out in the Paris agreement, only got tougher. A report released by the Global Carbon Project, a group tracking greenhouse gas emissions, indicated that levels of heat-trapping carbon dioxide are likely to grow in 2017, after a three-year plateau.

The report found that progress is being undercut by fossil fuel pollution in countries with growing industries, such as India and China.

Even before the bad news, the 175 parties signed on to the Paris deal were struggling to reduce greenhouse gas emissions enough to reach the 2-degree goal. The conference in Bonn is expected to address what contribution each participant needs to make and how to track that progress.

“Paris was a love affair. Now you have to make the marriage work,” said Dan Kammen, a professor of energy at UC Berkeley who has long followed international efforts to address climate change.

Brown’s European visit is paid for by the nonprofit California State Protocol Foundation, with some of his aides receiving money from the nonprofit Climate Registry and Climate Action Reserve, according to spokesman Evan Westrup.

Antonio Tajani, president of the European Parliament, praised the governor for making the trip even as Trump and his top officials stayed home. The small Washington contingent is there because the U.S. can’t legally pull out of the Paris pact until 2020.

“The approach of Mr. Trump is not necessarily as helpful as it might be,” Tajani said. “But we are delighted to have Gov. Brown here because this shows there is a strong commitment from the U.S.”

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com

Twitter: @kurtisalexander