Their encounter underlined the extent to which Trump, as he pursues an "America first" foreign policy, is being sidelined on the world stage. Xi spent nearly an hour talking to Brown, one of the administration's loudest, most powerful critics on the environment.
They discussed global warming and green technology in the Great Hall of the People, a granite-columned building on Tiananmen Square reserved for high-level dignitaries, political gatherings and ceremonial occasions.
"It's highly significant that the governor of California can meet with the president of China and talk about the foremost issue of our time," Brown said, sounding especially jovial on the third day of his weeklong China tour. "It's very clear he welcomes an increased role on the part of California."
Xi emphasized the state's unique economic impact and encouraged California to promote ties on the local level in science, innovation and green development, according to a statement from China's Foreign Ministry.
Brown started his trip with visits to the southern Chinese cities of Chengdu and Nanjing, where he repeated his grim warnings about climate change and signed agreements on clean energy.
Xi "has definitely given the green light for more collaboration between China and California and, I would say, other states through this subnational-level arrangement," Brown said.
The leaders' discussion appeared as much about symbolism as substance.
"He vaults over the parochial sense of governor to governor, and he vaults into the world of state to nation," said Orville Schell, director of the Asia Society's Center on U.S.-China Relations in New York, who wrote a 1978 biography of Brown.
The meeting built on a relationship that started when Xi's father met Brown in California nearly 40 years ago during his first round as governor. Brown greeted Xi when Xi visited Los Angeles in 2012 as China's vice president. They spoke again in Rancho Mirage during a 2013 summit with
California has worked with China on environmental issues for years, including zero-emissions vehicles and air pollution control. Chinese officials recently asked the state for guidance with a carbon emissions trading market they plan to launch this year.
"China is making a substantial contribution, as are other places in the world, and we are stepping up the effort," Brown said.
The two met soon after the top U.S. diplomat in China resigned in protest of Trump's Paris decision. Embassy spokeswoman Mary Beth Polley confirmed the departure of David Rank — a career diplomat since 1990 who was set to be replaced by Trump's pick for ambassador — but said only that it was a personal decision.
Their conversation also took place on the first day of an international clean energy forum in Beijing, where the Paris decision threatened to turn a mundane meeting of global energy ministers into a raucous debate about national sovereignty and renewed ambitions for an ailing planet.
This is China's first time hosting the Clean Energy Ministerial, which began amid the city's characteristic sheen of haze. The eighth annual event resembles something between a trade show and a leadership conference. Clean tech companies camp out in over-lighted booths. Energy leaders swap ideas at lengthy panels.
The U.S. organized the first ministerial in 2010, an attempt to salvage opportunities after the 2009 Copenhagen climate talks fell apart. San Francisco hosted the event last year.
The attendance list now clearly illustrates America's climate divide. On one side is the liberal Brown; on the other, Perry, a big-oil conservative and former Texas governor who supports the fossil fuel industry. The split gives China an opening to portray itself as an alternative global leader on green energy.
"Hosting the ministerial is a big statement about where China has pledged its future and a kind of assertion of leadership," said Isabel Hilton, a founder of Chinadialogue, a website that focuses on environmental issues.
Perry arrived at the forum defensive. Trump's decision lumped the U.S. with Syria and Nicaragua, the only other countries that were eligible to sign the Paris agreement but didn't do so. China and the Obama administration negotiated the deal, and China has vowed to stay in it.
"We're not stepping back and we haven't created a void," Perry told reporters on Monday in Tokyo en route to the meeting. "I hope China will step in and attempt to take the mantle away. It would be a good challenge for them."
The green push belies another truth: China is the leading emitter of greenhouse gases and the biggest global funder of new coal-powered projects. More than 60% of its energy use is tied to fossil fuels.
But the nation has also become the largest investor in renewable energy, and the world's biggest producer of solar power. It plans to pour $361 billion into clean energy by 2020.
"They've realized that climate change is not just a burden; it can be turned into an opportunity," said Xu Yuan, a climate change expert and professor at the Chinese University of Hong Kong.
America's green tech companies also see opportunity.
"China's economy is huge, their role in the world is huge, and they're going to be leaders in this space by orders of magnitude," said Jim Wunderman, chief executive of the Bay Area Council, an advocacy group for the region's businesses, which helped host the ministerial last year and brought a delegation to Beijing during Brown's visit.
The governor's presence here helps make meetings possible, Wunderman said. "He carries the flag for the state."
Meyers is a special correspondent.
Times staff writer Jon Kaiman and researchers Nicole Liu and Gaochao Zhang in the Times' Beijing bureau contributed to this report.
4:19 p.m.: This article has been updated with background information.