The Democratic governor enjoyed an enthusiastic reception from a packed room of nurses wearing red shirts at the National Nurses United conference in San Francisco. The union was a strong supporter of Brown in his 2010 gubernatorial race and helped him win voter support for his initiative raising the state's sales and income taxes last year.
"You're a hell of a lot more radical, and forward and progressive than I am," the governor said. "I can't push you. You got to push me, but together we'll push our country to a much better place."
Brown referred to recent data that show carbon dioxide was measured at 400 parts per million at the oldest monitoring station in Hawaii, which sets the global benchmark. The last time the worldwide carbon level was probably that high was about 2 million years ago, some researchers estimate.
"The last time that happened ... sea level was 60 foot higher, in other words, we'd be under water right now," Brown said. "The scientific consensus is, we need to take action."
Brown said the nurses should use their organizing might to tell the public that the survival of future generations is at risk.
He said focusing on climate change also could help the union remain relevant, as labor union membership erodes each year.
"If the American labor movement wants to grow instead of shrinking every year, the only way it's going to get there is organizing with not just the immediate, but with the largest sense of what we have to do as men and women of this country," Brown said.
The nurses were later joining a rally at the Golden Gate Bridge opposing the contentious Keystone XL Pipeline.
The union was instrumental to getting Brown into his latest term as governor, staging animated rallies during his 2010 campaign in which people dressed as royalty mocked his wealthy Republican opponent, Meg Whitman.
It was later revealed that the union helped Whitman's former maid, an illegal immigrant, go public with her story, helping sink Whitman's campaign.
"Of all the unions I'm talking to, nobody has a better global vision than nurses," Brown said to big applause. "If you can link your immediate occupational objectives with the larger sense of what we need to do as human beings, you become a very powerful organization."