With Donald Trump poised to enter the White House in a few weeks, America's role in the fight against climate change looks threatened. The president-elect and confessed climate-change skeptic's cabinet and agency picks similarly deny the existence of climate change, and have strong ties to the fossil fuel industry. Trump has also signaled he may withdraw from the Paris climate agreement.

But in California, America's most populous state and a leader on climate protection, those driving the transition say even a Trump presidency can't stop an energy revolution that's already in full swing.

Talking to the media, Alberto Ayala, deputy director of the California Air Resources Board (CARB), is adamant: "It won't change anything for us. And California isn't the only state that thinks so."

Even as California's economic power more than doubled since 1990, greenhouse gas emissions fell by 23.5 percent.

With some locations in California not having seen rain for four years, climate change is a reality in the state

Cities forge the way forward

Cities like Palo Alto are showing how it's done. As far back as the 1960s - when roads were being expanded elsewhere - Palo Alto introduced a comprehensive network of bicycle paths.

Over the last 15 years, it has reduced its water consumption by 40 percent, while the economy boomed and the population expanded.

Mayor Patrick Burt says Palo Alto has proved switching to renewables makes economic sense

But perhaps its most notable achievement is on emissions. "Since 1990, we've been able to cut our greenhouse gas emissions by more than 35 percent," Mayor Patrick Burt says.

That's been possible because Palo Alto bought in the local energy provider and set clear business targets. Since last year, 100 percent of the city's electricity supply has been covered from renewable sources, the mayor says.

And that sends a message to other cities, that switching to renewable pays - even here in the United States. "We have made the transition to renewables, at a cost more than 30 percent lower than what the neighboring energy supplier that has fossil fuels in the mix charges," Burt explains.

A question of economics

Over half of the United States' million solar power installations are located in California. More than half of the 500,000 electric cars on American streets are in cities like Los Angeles, San Francisco and San Diego.

Debbie Raphael, director of the San Francisco Department of the Environment, says these developments show just how much local efforts can achieve. "The cities in the US gave up waiting for Washington a long time ago," she says.

And Craig Lewis, Executive Director for the Clean Coalition, an energy transition group based in northern California, says this is just the beginning: "The Californian electro-mobility revolution is picking up speed. The rest will follow - because it has to follow."

Palo Alto's mayor believes that just as renewables are now winning the price war in the power sector, the greener option will prove to also make the most economic sense in fields like transport.

San Francisco environment chief Debbie Raphael says cities aren't waiting on Washington to go green

"With our last agreement, we bought solar power at 3.7 cents per kilowatt-hour," Burt says. That makes electricity from coal-fired power stations twice as expensive as its solar competitor.

But will a President Trump, who appointed key figures from the fossil fuel sector to his cabinet, bow to the laws of the market economy?

Grounds for optimism

Jigar Shah, an investor in green start-ups and mature solar businesses, says a look at past American heads of state gives grounds for optimism. "George W. Bush advanced wind and solar energies like no other US president." That took many observers by surprise.

And employment figures - well beyond California itself - reveal the risks Trump would take if he tried to undo progress made thus far.

Hundreds of thousands of American jobs rely on the renewables sector

The US solar industry currently employs 240,000 people, compared to 70,000 who work in the coal sector. A coal renaissance would likely lead to job losses elsewhere - raising serious questions for the administration.

Palo Alto is sending clear signals on which direction its economy is to move in. The city has confirmed its decision to reduce greenhouse gases by 80 percent by 2030.

And the list of start-ups the city wants to help achieve this goal don't look like they're about to give up.