“I’m on the side of the angels,” the former Jesuit seminarian said in an interview before flying on Friday to China, where he will rally support for his climate policies next week. “I’m going to do everything I can, and people are going to join with me.”

Brown, now 79 and in his final term, has long championed environmental causes, promoting conservation and smog-related policies when he was governor before, from 1975 to 1983, and overseeing a dramatic expansion of California’s greenhouse gas reduction standards since returning to office in 2011. Roughly 170 jurisdictions, including Canada and Mexico, have endorsed Brown’s nonbinding agreement embracing efforts to limit global temperature rise to below 2 degrees Celsius, the threshold beyond which many scientists predict catastrophic consequences.

But world leaders, not governors, sign international agreements with the force of law, and for years, Brown was relegated to a supporting role. Only after the election of Trump, who has called climate change a hoax, did Brown’s climate diplomacy find new prominence as a counterweight to a Republican-held White House.

“If Obama was still in office, this phenomenon would not be occurring,” said former California Gov. Gray Davis, Brown’s onetime chief of staff. “But Jerry keeps pushing … People, when they think of climate change, see Jerry Brown as a legitimate alternative [to Washington]. It’s not make believe. It’s real.”

For a politician, Davis said, “Timing is everything in life.”

Brown, who has called climate change the “existential threat” to humanity, has at times questioned whether it is too late to avert calamity. While campaigning for Hillary Clinton last year, he said it would be “game over” for climate change if Trump were to win.

But last week, when it remained unclear whether Trump would withdraw from the Paris agreement, Brown predicted that the president is a political “realist” and that progress on the issue may be “not as disastrous as we thought a few months ago.” Trump had visited the Vatican, where Brown spoke about climate change in 2015, and was pressed by European leaders to remain in the accord.

If Brown, like the Europeans, was seeking to nudge Trump with his remarks, he abandoned all niceties after news of Trump’s decision emerged.

Following Trump’s Rose Garden announcement Thursday, Brown told reporters, “Today’s announcement is tragic in a fundamental way. But it’s also, I guess, to be expected.”

He called the withdrawal “insane” and said, “California will resist.”

Brown and the governors of New York and Washington said they would establish a coalition of states committed to upholding the Paris accord, while 27 California state senators sent a letter to Brown, urging him to convene a climate summit with “like-minded states and subnationals from around the world, to ensure that we continue to charge ahead without forfeiting all of our historic progress to date.”

California has long served as a model on climate change policy, sharing extensive regulatory experience with bureaucrats abroad. Severin Borenstein, an energy economist at University of California, Berkeley, said, “What California does isn’t just sort of closely watched. In some cases, it is just photocopied into other states and other countries.”

But Trump’s disengagement from international climate politics has left open a political opportunity for Brown, with climate-minded politicians abroad running into resistance in Washington seeking other partnerships in the United States. Even if Trump had moved to remain in the Paris accord, his rejection of mainstream climate science was broadly seen as increasing the significance of climate change efforts at the local and state level, with California at the forefront.

“The absence of a real federal policy has created a vacuum, a hunger overseas for what are Americans doing on climate change. And into that hunger, Jerry Brown offers a menu,” said David Victor, professor of international relations at the University of California, San Diego, and author of the book “Global Warming Gridlock.” “He’s just kind of nominated himself. But I think that’s the nature of the business.”

In his feud with Trump, Brown has been aided by the president’s myriad domestic controversies and low public approval rating – and by the freedom a governor can exercise in his final term.

When he last visited China, in 2013, California was emerging from a budget crisis and Brown devoted much of his attention to trade-related concerns. This time, he is expected to focus almost exclusively on climate, participating in a global climate summit and meeting with high-level Chinese officials, possibly including President Xi Jinping.

Earlier in his governorship, said Orville Schell, director of the Center on U.S.-China Relations at the Asia Society in New York, Brown “had just sort of begun to clean up the financial mess in the state, and he was just beginning to look out. But he hadn’t fully developed this idea, which is now in sort of full fledge, that California ought to start acting like a country.”

“He didn’t have the pretention that the state should or could play a global role,” said Schell, who wrote a biography of Brown in 1978 and remains in contact with him. “It’s relatively recently that he’s thought, ‘My God, I’m a pilot of a supertanker in its own right that’s bigger than most countries in the world. Let’s put this baby to the test.”

Brown, who ran unsuccessfully for president three times but is now seeking no higher office, has little to lose. His public approval rating remains high in a heavily Democratic state that contributed significantly to Trump’s loss of the popular vote last year, and the state Legislature has pushed forward with a raft of climate legislation to gird against Trump administration policies.

Earlier this week, the state Senate passed one bill requiring utilities to obtain 100 percent of their electricity from renewable sources by 2045 and another folding Obama-era water, air and endangered species standards into state law, preserving them in California, regardless of reversals at the federal level.

According to a Public Policy Institute of California poll in February, more than 6 in 10 Californians support state action to address global warming. Bill Whalen, a research fellow at Stanford University’s Hoover Institution and former speechwriter for Gov. Pete Wilson, said Brown “could basically go to Beijing and dance on table tops and there wouldn’t be much hell to pay back home.”

Still, Trump is capable of punishing force in any collision with Brown. Earlier this year, the president directed administration officials to begin dismantling Obama’s Clean Power Plan, and his administration has left open the possibility that it could revoke California’s authority to set its own, more rigorous clean air standards under a federal waiver from the Clean Air Act.

Defending a massive cut proposed by Trump to the Environmental Protection Agency, White House Budget Director Mick Mulvaney dismissed climate change programs as “a waste of your money” and said the administration is “not spending money on that anymore.”

Brown demurred this week when asked if he considers himself a leader in the climate-related resistance to Trump, saying, “I’m not going to characterize my role here.” But he lamented the passage of time since he attended a landmark climate summit in Rio de Janeiro in 1992.

“Now we’re 25 years later, we’re four presidents later, and it’s time we got going,” he said. “People know what the science is telling them, and we’re not going to make it in any kind of prosperous way if we don’t reverse this carbon dependency.”

As for what he will tell Chinese officials about his adversary back home, Brown said, “I don’t think I’ll have much to say about the president.”