On Sunday, Donald Trump told Fox News that “nobody really knows” whether climate change is real. But scientists who staged a rally in San Francisco on Tuesday had a stinging rebuke for the president-elect: It’s real, it’s here, and we are bracing for an epic battle against your policies and appointments.

“The election result was not the one that many of us would like to see, but the battle goes on and must go on,” Michael Mann, director of the Earth System Science Center at Penn State University, said at the rally.

Mann spoke outside the Fall Meeting of the American Geophysical Union, where 26,000 scientists are gathering in the first major convening of climate scientists since the presidential election. He was joined by other climate researchers and activists representing Native Americans and people living in “frontline communities” near polluting refineries, power plants, pipelines, and other fossil fuel infrastructure.

The rally, called “Stand Up for Science,” was organized by ClimateTruth.Org and The Natural History Museum, a self-described “mobile and pop-up museum that champions bold climate action.”

“It’s critical that scientists step forward and make our voices heard, not just for the sake of scientific research but for the sake of the entire planet,” Mann said. “We have our work before us.... This is our home. It’s time to start acting like it.”

Kim Cobb, professor of earth and atmospheric sciences at Georgia Institute of Technology, said hundreds of scientists attending the conference were at the rally.

“We have, for too long as scientists, rested on the assumption that by providing indisputable facts and great data we are providing enough of an attack to counter the forces against science,” she told the crowd. “Obviously, that strategy has failed miserably.”

“We need all scientists who care deeply about their work, the facts, and the truth to shake off all fear that holds them back from engaging in this space,” Cobb said. “It’s time. It’s past time. If we do speak together, I am confident we can change the course of history.”

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In an interview, Beka Economopoulos of the Natural History Museum said, “We’re thrilled there are dozens of scientists getting up from the labs and into the streets, and I anticipate we will see more of this. Our biggest message is the role for scientific institutions standing up for science.”

Economopoulos said the rally underscored points made in recent weeks by thousands of climate scientists who have signed petitions, written open letters to the president-elect, and organized colleagues to take action.

“In the wake of the election, we’ve seen antiscience and climate-denier forces gain unprecedented power, and science is under attack,” she said. “The Trump administration proposes to gut or ax science funding, dismantle our climate and clean energy policies, and has appointed climate deniers with ties to the fossil fuel industry to key cabinet positions and asked for the names in the Department of Energy of all employees who have worked on climate change in what has been referred to as a witch hunt.”

Requests for comment from the Trump transition team were not returned.

Around the world, scientists and activists are bracing for what they say will be Trump’s dismantling of laws and regulations that protect clean air and water, limit greenhouse gas emissions, and restrict drilling and mining offshore and on public land. Other concerns include Trump’s pledge to withdraw from the Paris climate agreement.

(Photo: ClimateTruth.org)

“It’s a nightmare,” Kierán Suckling, executive director of the Center for Biological Diversity, said in an interview. “This is the wealthiest, most corporate, most climate-denying cabinet in the history of our government, and we’re going to be looking at assaults on any efforts to rein in global warming by a unified front throughout the entire federal government.”

His biggest fear? “That this new administration is able to structurally undermine these agencies such that the impact is going to last for decades rather than just the four years [it’s] likely to get,” he said.

First on the chopping block: President Obama’s Clean Power Plan, which requires all new and upgraded power plants to comply with federal Clean Air Act greenhouse gas emissions standards. The rule is enforced by the U.S. Environmental Protection Agency, which will likely be headed by Kansas Attorney General Scott Pruitt, an energy industry ally and climate-change denier.

“It’s the No. 1 target of the head of the EPA because that rule, more than any other, is hated by the oil and gas industry,” Suckling said, adding that industry will overturn many Obama policies simply by taking the government to court.

“A lot will be done through the sue-and-settle tactic,” he said. “Industry will file suits, and the administration will simply settle them. It’s the fastest, easiest way for industry to change policy. The rule-making procedure is long and complicated and has to be approved under scientific legal standards. This way it’s just presto, and Obama energy policies disappear.”

Suckling added that Trump will “undermine the political ability of cities and counties to go forward with fracking bans” and create a free-for-all for fossil fuel extraction on public lands.

“The ‘Keep It in the Ground’ movement has gained some steam in the last four years, but with Trump and his bevy of oil industry executives, we’ll see a huge ramp-up in oil, gas, and even coal mining on public lands,” Suckling said. “We’re rapidly progressing into becoming the United States of Oil.”