That, along with Trump’s appointments of a climate-change skeptic to lead the Environmental Protection Agency and a current oil executive to be secretary of state, has rattled the science community. Scientists called the actions an assault on hard data. “Ice has no agenda, it just melts,” read one of their posters.

“If you told me I would be here five years ago, I wouldn’t believe you,” said Kim Cobb, a professor at Georgia Tech’s School of Earth and Atmospheric Sciences. “We have for too long as scientists rested on the assumption that, by providing indisputable facts and great data, that we are providing enough of an attack against the forces against science. Obviously that strategy has failed miserably.”

Despite Trump’s assertions, there is broad scientific evidence that climate change is real and is driven by human activity. Since 1998, the Earth has had its 10 warmest years since record-keeping started in 1880. Industrial manufacturing and the use of fossil fuels are two of the biggest drivers of global warming, an Intergovernmental Panel on Climate Change report said.

The speakers — scientists and activists — waved signs in a plaza near Yerba Buena Gardens and said they were incredulous that Trump would deny hard facts and evidence. A vein of fear ran through the speeches: that their life work would be disavowed, or that they would soon be ostracized for it. Recently, the Department of Energy denied a request by Trump’s transition team to list employees who had attended climate-change meetings.

“We are at a moment in history where we have to do something,” said Naomi Oreskes, a history of science professor atHarvard University. “This is a frightening moment. We have seen how the reins of the federal government are being handed over to the fossil-fuel industry.”

Laura Nielsen Lammers, an associate professor at UC Berkeley’s department of environmental science, policy and management, said she worries about how her 7-month-old infant son’s life will be impacted by an administration focused on denying climate change.

“More than ever, people are concerned about the fate of the planet,” she said. “We need solid science. As a new mom, I’m honestly really scared. ... I’m hoping more awareness will prevent huge funding attrition to study areas like clean water and air.”

The group publicly encouraged their colleagues to fight for their research and beliefs.

Peter Frumhoff, director of science and policy at the Union of Concerned Scientists, said evidence has served as the bedrock for public policies. He worried that will no longer happen.

“The president-elect himself says nobody knows if climate change is real,” Frumhoff said as the crowd booed loudly. “Science and evidence is at risk. It is on us to ensure it is protected.”

Lizzie Johnson is a San Francisco Chronicle staff writer. Email: ljohnson@sfchronicle.com Twitter: @LizzieJohnsonnn