California’s hard-charging green governor is shaking things up once again on the world stage.

As President Donald Trump and other world leaders gathered in Hamburg, Germany, for the G20 summit, Gov. Jerry Brown on Thursday made waves by telling the world that Trump — who has decided to withdraw the United States from the 2015 Paris climate accord — does not speak for most Americans when it comes to dealing with environmental concerns.

Then Brown announced that California would host a global summit on climate change in San Francisco in September 2018.

“Yes, I know President Trump is trying to get out of the Paris Agreement, but he doesn’t speak for the rest of America,” Brown said in a video message shown to tens of thousands at the Global Citizen Festival in Hamburg. “We in California and in states all across America believe it’s time to act. It’s time to join together, and that’s why at this Climate Action Summit we’re going to get it done.”

The governor’s latest action on climate change is arguably his most politically aggressive yet — and immediately drew high praise and howls of criticism.

“It’s brazen on several levels,” from “stepping on the president’s trip” to “thinking he speaks for the American people,” said Bill Whalen, a longtime GOP strategist who is now a research fellow at Stanford’s Hoover Institution. The San Francisco summit is not likely to accomplish much, Whalen said, besides gathering people to “collectively thumb their nose at the American president.”

“To what end will this conference change anything other than pumping more carbon in the atmosphere as people fly from all over the world to get here?” Whalen asked. “It’s not going to change climate change policy in America, and it’s not going to change Donald Trump’s mind.”

Brown has vowed to place California, along with its jumbo-sized, world-class economy, at the vanguard of governments trying to meet global warming head on. Last December, Brown said the Golden State would put up “its own damn satellites” if Trump cuts funding for projects that gather climate data from space.

And on Thursday the governor once again threw down the gauntlet. He invited “entrepreneurs, singers, musicians, mathematicians, professors” and others who represent “the whole world” to the summit.

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Jerry Brown: While President Trump is `AWOL,’ China is emerging a climate leader Brown has waged a public campaign to counter Trump since the president declared in June that the U.S. would pull out of the 2015 Paris accord reached by nearly 200 nations to reduce greenhouse gas emissions. Shortly after Trump’s announcement, Brown traveled to China, warning that “disaster still looms” unless governments around the world take urgent action. On that trip, Brown predicted that Trump’s decision to withdraw from the Paris accord would prove to be only a temporary setback, thanks to firm commitments by China, European countries and individual U.S. states to pick up the leadership role vacated by the president.

“President Trump, he’s going off the reservation hopefully for a month, a year, not much longer,” Brown told the Mercury News and East Bay Times before departing for China. “If he stays on his present course, California will just redouble its efforts and the people of the world will have to rise up and take action. And I think in a very paradoxical way, that’s exactly what Trump is stimulating — the very opposite of climate denial is climate activism.”

John Cox, a San Diego County businessman who is one of several Republicans running to succeed Brown, said in an interview Thursday that “there would be screaming across the media everywhere” if a red-state governor had done the same while President Barack Obama was in office.

“Mr. Brown,” Cox said, “has been trying to position himself as a leader on foreign policy from his perch as governor of California.”

The White House did not respond to a request for comment.

In response to the criticism, Brown’s office pointed to a statement the governor made to the New York Times: “It isn’t being cooked up because of Trump. No nation or state is doing what they should be doing.”

According to Brown’s advisers, the September conference will be the first meeting an American state has hosted to support the Paris agreement. Former United Nations climate chief Christiana Figueres — who introduced Brown to festival-goers as “a stubborn optimist from a surprising country” — said the global meeting will send a strong message that the president is not speaking on behalf of all Americans, most of whom believe climate change poses real threats to everyone on the planet.

The annual Global Citizen Festival has drawn huge crowds and featured remarks from Canadian Prime Minister Justin Trudeau, Norwegian Prime Minister Erna Solberg and Argentinian President Mauricio Macri, along with performances from Coldplay, Shakira, Pharrell Williams and others. Newsweek reported Thursday that Trump was not invited.

The San Francisco summit, to take place ahead of the 14th United Nations Framework Convention on Climate Change, will be part of a larger effort around the globe to recruit and lobby governments and municipalities to make good on pledges to fight climate change, according to Brown’s office.

Asked how the event would be paid for and if public money would be used, a governor’s spokesman Thursday responded that the funding details had not been determined.

Earlier this week, Brown joined the leaders of Baden-Württemberg, Catalonia and South Australia — all members of the Under2 Coalition — to urge the G20 to reaffirm its support for implementation of the Paris Agreement and to recognize the role of sub-national governments, states, regions and cities, in leading and delivering on climate action.

“All over the world, momentum is building to deal seriously with climate change,” Brown said in a statement. “Despite rejection in Washington, California is all in. We are fully committed to the Under2 Coalition and the Paris Agreement.”