Gov. Jerry Brown was about to leave Mexico’s capital after four days of talks pressing on the environment, and he wasn’t sure, broadly speaking, how his diplomacy might add up.

Meetings held out of public view – dinner with business magnate Carlos Slim and talks with the poet Homero Aridjis and Cuauhtémoc Cárdenas Solórzano, a founder of Mexico’s Party of the Democratic Revolution, among others – were “more critical” on any number of issues, Brown said, than was on display at his official functions.

“Some of the more private guys,” Brown said, were “not that optimistic” that people are interested in climate change.

“California can’t keep pushing a climate change agenda if more states and countries don’t do the same thing,” Brown said. “You can’t do a carbon price all by yourself forever.”

Brown, a longtime advocate for environmental causes, is trying in his third term to export California policies to reduce carbon emissions. His plan is to use his reputation – and that of California – to rally support in other states or countries for policies they can promote together in international climate talks, first this year in New York and Lima and then next year in Paris.

It is the Paris meeting, where countries are expected to adopt a global treaty on climate change, that Brown recently called “the crucial event for the future of the world.”

Yet as substantial Brown’s record on the environment may be, he is only a governor, and it is unclear even to him if he would have a place at a meeting where presidents’ names are called.

“Might not, I don’t know,” Brown said in an interview in the lobby of his hotel. Brown, who set a bag of rice cakes on the table in front of him and wondered if the green tie he was wearing was too bright, said it “depends upon what I’ve been able to do in the meantime, if there’s any particular role.”

“I’m not going to go and just sit on the sidelines.”

Brown is not overly optimistic about the prospects for global warming. He worries about levees collapsing and fresh water running out.

“Well, you’re going to be around for more of this climate change than I am,” the 76-year-old said, “and it ain’t going to be pretty.”

Still, his reception in Mexico was warm, and if Mexican officials want to work with him, Brown said, “That’s something.”

Brown’s wife, Anne Gust Brown, was sitting beside him in the hotel. She said “our best hope is that there’s some technological solution that doesn’t exist, some carbon capture or something that doesn’t exist, because actually inflicting pain on people in the short term is very hard.”

Gust said “businessmen here tend when they think about it and believe in climate change, tended to talk more about technological solutions.”

But Slim is one of the richest people in the world. If he invited Brown for dinner, perhaps he is on board?

“I’m not going to comment,” Brown said. “After being welcomed into his house, I don’t want him to read a nasty story I might not be invited back.”