Ninety-seven percent of climate scientists agree that human activities are the leading cause of steadily rising temperatures around the globe.

President-elect Donald Trump, however, has called global warming "bulls**t" and a "hoax," making him soon to be one of, if not the only, world leader to deny the science behind climate change. He's also threatened to defund the Environmental Protection Agency and bring back the flagging coal industry.

Not surprisingly, environmentalists and climate activists are alarmed by what a Trump presidency will mean for efforts to reduce human-generated emissions that are warming the planet.

And they wonder what Trump's policies might mean for California, which is considered a pioneer in efforts to conserve the environment and fight climate change.

Trump has signaled he will roll back progress on climate change at a national level

Under the Obama administration, the United States was on track to regulate carbon dioxide emissions from power plants as part of the Clean Power Plan. The U.S. had also signed onto the Paris climate agreement, which took effect earlier this month, and had pledged to cut greenhouse gas emissions by 26 to 28 percent, compared to 2005 levels, by 2025.

Now the future of both those actions are in question. Trump has said he wants to pull out of the Paris agreement and scrap the Clean Power Plan, while scrapping other Obama environmental regulations.

California has been working to reduce its greenhouse gas emissions since the passage of AB 32 in 2006. The state has already reached the goals envisioned under the Clean Power Plan  and is on track to cut even more.  The state has largely relied on a cap-and-trade program, in which regulators set limits on carbon emissions and allow polluters to buy and sell carbon permits to stay under those limits.

As it stands now, the Clean Power Plan would give California opportunities to trade emissions permits with neighboring states and to be a model for them as they develop their plans to comply with the new regulation.

But the future of the Clean Power Plan is unclear under a Trump administration. The rule has been challenged in federal court. Trump could choose to no longer defend it, and he could appoint a new justice to the Supreme Court who favors overturning it.

California will likely continue with its efforts to reduce greenhouse gas emissions, even without the Clean Power Plan.

Instead, for Californians, Trump’s election means a return to the days of President George W. Bush, when the state operated largely on its own in terms of climate and environmental policy. After all, it was under the Bush administration that California passed AB 32, the first-of-its-kind climate legislation, and it did so precisely because of federal inaction on climate change, according to Cara Horowitz, co-executive director of the Emmett Institute on Climate Change and the Environment at UCLA’s law school.

California’s climate policies are not threatened by a Trump presidency

Passed in 2006, AB 32 required California to reduce its greenhouse gas emissions to 1990 levels by 2020. Since then, the state has reduced its emissions by over 7 percent, as the population has increased by the same amount. This fall, another landmark bill deepened and extended those cuts. SB 32 commits the state to cutting emissions by 40 percent below 1990 levels by 2030.

In the meantime, California has rolled out a suite of programs to help the state meet its emissions reduction goals, the most well known of which is cap and trade. Regulators slowly decrease the cap over time. Polluters who lower their emissions below the cap can make money by selling carbon credits to power plants, refineries and other polluters that can't meet their targets. The program is meant to incentivize efforts to reduce pollution.

Trump can't overturn California's cap-and-trade program (although it is currently embroiled in a state lawsuit challenging its legality).  Nor can he overturn SB 32.

“We’re too committed as a state, and frankly we have too much as a state to back down on our climate policies,” said Horowitz.

From the worst drought in half a millennium, to a long coastline vulnerable to sea level rise, to a wildfire season that is 78 days longer than it was in 1970, Californians "see the effects of climate change every day and we’re very committed to our climate policies, no matter what happens at the federal level," Horowitz said.

Who Trump appoints to head federal agencies will likely have a huge impact on California

Beyond climate, President Trump’s attitudes toward the environment will resonate most deeply in traditional environmental issues: things like clean air, clean water, endangered species, land conservation and energy development.

One way to tell how he’s leaning is to track who is appointed to head agencies tasked with safeguarding or developing those resources, according to Ann Notthoff, California advocacy director at the Natural Resources Defense Council.

Trump has surrounded himself with climate change deniers, oil industry executives, and lawmakers from fossil fuel-dependent states like North Dakota who are eager to expedite production of oil, gas and coal from federal lands.

Notthoff said she is especially keeping her eye on who Trump appoints to head the Department of Interior, which oversees agencies like the National Park Service, the Bureau of Land Management, the U.S. Fish and Wildlife Service and the Bureau of Reclamation.

Trump himself has pledged to increase oil and gas production on federal land, which fell under the Obama administration. That could impact California, the nation’s No. 3 oil state, where 7 percent of oil wells are on federal land, according to the BLM.

Trump's EPA, in particular, will affect clean air and clean water in California

Trump has threatened to eliminate the EPA entirely, although he recently walked back that comment, saying he wants to focus the agency on ensuring clean air and water. But there are many ways to do this, some of which are top-down and regulatory, while others are more voluntary and market-based.

One of the ways the EPA has traditionally ensured clean air and drinking water is creating emissions and concentration standards that polluters have to meet, enforcing them with penalties, and passing stricter ones over time. Horowitz worries a Trump EPA will let that approach slide, becoming business- and industry-friendly at the expense of public health. “It’s very clear he’s one of those Republicans who sees environmental protection and business interests at odd with each other, as opposed to things that can and should co-exist,” she said.

California is legally allowed to pass state standards that are stricter than federal ones, but Horowitz says that’s difficult. “Without a really robust federal partner, we could see California’s progress on air quality slipping.”

California benefits from federal support for renewable energy, which a Republican-controlled Congress could cut off

Last December, lawmakers cut a deal to extend federal tax credits for the wind and solar industries through 2017 and 2019 respectively. The deal would need congressional approval to be extended. And it could even be cut off prematurely, writes solar energy columnist Christian Roselund.

Trump has previously expressed his distaste for federal subsidies for clean energy. According to a memo released in late October, Trump pledged to “cancel all wasteful climate spending,” according to the Washington Post. Investors are clearly already worried: Solar stocks plunged following news he had won the election.

This has huge implications for California, which has nearly half of the solar power generation in the country.

“Subsidies at the federal level can all have a role to play in how effectively we deploy clean energy, how much it competes on a playing field with fossil fuels,” Notthoff said.

However, as with climate change policy, state policies encouraging solar development will not be affected by this election.

California’s newly minted National Monuments likely to stay in place

Under the Antiquities Act, President Obama created a number of national monuments in California in the past eight years, including the San Gabriel Mountain National Monument in 2014. Experts say it’s highly unlikely that President Trump would reverse those designations because they've mostly received bipartisan support, and it's unclear the Antiquities Act allows presidents to strip monument designations from locations that already have it.