Tens of thousands of scientists and their allies marched through Manhattan Saturday to protest President Donald Trump’s approach to science, including his job picks for top regulatory posts and proposed funding cuts to research and enforcement.

The March for Science, coinciding with Earth Day, was set for more than 600 locations worldwide, including Stony Brook and Washington, D.C., the anchor city, from the Brandenburg Gate to Gainesville, Florida.

“Science Is Not a Liberal Conspiracy,” read one sign at the Manhattan protest. “Stop the War on Facts.”

“I don’t know that there’s anything that cuts closer to home than life or death,” Peter Haugen, 45, a psychologist from New Jersey, said of Trump’s proposed budget cuts to the National Institutes of Health: 18.3 percent, about $5.8 billion, cuts he said would imperil the fight against disease and illness.

Christina Lowenstein, 55, of Manhattan, stood on Broadway handing out pink pro-science paper caps with cat ears in the style of the hats worn by pro-Hillary Clinton supporters critical of Trump.

“We can’t believe we even have to say that we’re in favor of science, quite frankly,” she said.

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The pageant of scientists, many wearing white lab coats, parading through the streets is rare: the profession rarely pickets, instead seeking to stay apolitical.

But Saturday, as the crowd passed Trump International Hotel and Tower across from Central Park, thousands chanted: “Evil!” “Shame! “Hey-hey, ho-ho, Donald Trump has got to go!” and “Impeach!”

“What do we want? Evidence-based science! When do we want it? After peer review!” read a T-shirt worn for the occasion.

Kevin Lin, 31, who has a doctorate in math with a dissertation in the relationship between algebraic equations and geometry, said the Trump-led GOP was bad for climate-change research and pollution control.

“As long as we are focused on short-term profits, we are going to forget about the long-term issues,” said Lin, who went to graduate school at University of California, Berkeley, and now works as a software engineer.

Biochemist Megan Bourassa, 32, of Great Neck, marched down Broadway with a sign spaced to accentuate some elements from the Periodic Table: “LET US PAUSE 4 A MOMENT OF Sc I E N Ce,” for instance, with “Sc” was boxed to represent “Scandium”; “I” for “Iodine,” etc.

Bourassa, who holds a doctorate from Stony Brook University, said she’s troubled by Trump’s appointees, especially Rick Perry as secretary of energy, whose chief jurisdiction is the nation’s nuclear weapons. In 2011, he said he wants to abolish the agency.

“He basically wanted to shut it down and now he’s in charge of it!” she said.

Meanwhile, on the campus of her alma mater, about 500 people marched for three miles to support strict environmental regulations and affirm the scientific consensus that human action causes climate change.

“Climate change is bigger than anything,” said Bill Bauer, 71, of Dix Hills. “To think that the next generation might be impacted, I just can’t believe that 100 percent of parents aren’t concerned . . . how can you say it’s a hoax?”

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With Bauer was his daughter, Cassie Bauer, 29, of Stony Brook, who held a sign: “There is No Planet B.”

Trump responded to the Earth Day marchers protesting his skepticism of science and deep cuts to science funding with a statement saying he was committed to protecting the environment as long as it did not hinder economic growth.

In Manhattan, David Shire, 29, a doctoral student studying marine microbiology at Rutgers, stood on a corner near a police barricade holding a white board: “MAKE AMERICA SMART AGAIN For Once. 14% of population CAN’T READ.” “AGAIN” was crossed out.

Shire said he fears Trump’s proposed cuts would stymie the people who train to make vital scientific discoveries,many of whom are funded by the government.

“If you’re a professor and you want to take on a new student, you need money to pay for their research,” Shire said.

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Hofstra Urban ecology major and sustainability minor Kylie O’Toole, originally from Wrentham, Massachusetts, said she didn’t want to protest against Trump per se.

Holding a handmade sign playing off Hillary Clinton’s 2016 campaign slogan “I’m with HER,” an arrow pointing to a sparkled globe of earth, O’Toole said, “I like being with my people and see that I have support. It shows you’re not alone in your opinion.”

On the west side of the Trump building in Manhattan, Jim MacDonald, 67, an actuary from Flushing, Queens, taunted the demonstrators, holding up a “Thank God for Trump” sign. He said he resents what in his view is just the latest excuse to relitigate a grudge against the winning president he voted for.

“I’m angry, because these people are pretending to have a science march,” the Republican said, “when really it is this week’s anti-Trump march.”

With Jean-Paul Salamanca and Tom Brune