That choice marked a turning point for California. Under Democratic and Republican governors in the decades since, the state has approved pace-setting policies to require utilities to generate more of their electricity from renewable sources like solar and wind, promote electric vehicles and lower-carbon fuels, encourage conservation by “decoupling” utility profits from the amount of power they sell, and reduce total carbon emissions by 2020 to their level in 1990.

Brown is now finishing his fourth and final term as governor with a flourish. (He was elected in 2010 and 2014 after initially serving from 1975 through 1982.) Earlier this summer, the state announced it had met its 2020 carbon-reduction goal four years early. (He’s already signed legislation mandating another 40 percent reduction by 2030.) This week, Brown signed breakthrough legislation—authored by Kevin de Leon, the state Senate Democratic leader who is challenging Dianne Feinstein for a U.S. Senate seat—that commits the state to generating all of its electricity from carbon-free sources by 2045. He also signed a bill that attempts to block Trump’s plan opening six areas off the California coast to offshore oil drilling. And beginning Wednesday, he’s hosting government, business, and grassroots activists from around the world for a climate summit in San Francisco.

“We have a real program here that’s viable, difficult, but it’s very practical [and] very realizable,” Brown told me in an interview this week. “This is not about trying to get on a horse and flaunt whatever achievements we’ve got [in California]. We’ve got too far to go to be complacent or look backward.”

Yet looking backward is one way California can point the way forward: As Trump and his allies portray climate action as an economic threat, California’s record remains perhaps the most powerful rebuttal. “California is showing that climate policy can be … compatible with economic growth,” says Ann Carlson, a law professor at the University of California, Los Angeles.

Next 10, a nonprofit San Francisco–based research group, recently quantified the gains in its annual California Green Innovation Index report. From 2006 through 2016, the group reported, the state’s economy grew 16 percent and its population expanded by more than 9 percent. Yet over that same period, California cut its carbon emissions by 11 percent. Even as it squeezed emissions, California passed the United Kingdom to become the world’s fifth-largest economy.

California has succeeded most in transforming its electric-power sector. Reflecting its commitment to efficiency, the state’s per-person electricity use is down more than 7 percent since 1990 (while it’s increased more than 8 percent in the rest of America). Solar, wind, geothermal, and other renewables now account for about 30 percent of that electricity’s generation; the bill Brown signed this week commits the state to doubling that share by 2030, en route to carbon-free power by 2045. “California is showing that the transition can happen faster and cheaper than anyone thought possible,” Carlson said.