Protesters in Denver. Picture: David Zalubowski/AP

THOUSANDS of scientists, students and research advocates rallied in the US, Europe and Australia on Saturday to conveying a global message of scientific freedom without political interference.

The rallies began in Australia and New Zealand where thousands marched in support of science, the first of more than 500 marches globally triggered by concern over the rise of “alternative facts”.

The March for Science demonstrations come amid growing anxiety over what many see as a mounting political assault on facts and evidence and fears that research is being excluded from policymaking.

Supporters of science and research gather to take part in the March for Science protest in Sydney. Picture: Peter Parks/AFPSource:AFP

Vocal protesters in Sydney wearing white lab coats called on politicians to support the scientific community, carrying banners reading “without science, it’s just fiction” and “we need thinkers not deniers”.

Hundreds streamed onto the Washington Mall in Washington DC for a festive day of music, speeches and teach-ins by scientists disturbed by the rise of so-called “alternative facts” around crucial issues like climate change following the election of Donald Trump.

The marchers sought to present a united front, particularly against the Trump administration’s roll back of environmental protection policies and apparent lack of support for climate change.

Ice photographer and filmmaker James Balog, who says he has watched trillions of tons of ice melt, told the Washington crowd that talking about the science of climate change in the face of the Trump administration and climate change deniers is “a battle between objective reality and ideological fiction.”

People carry signs through Times Square in New York. Picture: Bryan R. Smith/AFPSource:AFP

“We didn’t choose to be in this battle, but it has come to the point where we have to fight because the stakes are too great,” said climate scientist Michael Mann, who regularly clashes with politicians.

President Donald Trump, in an Earth Day statement hours after the marches kicked off, said that “rigorous science depends not on ideology, but on a spirit of honest inquiry and robust debate.” Standing on the National Mall with thousands soaked by rain Saturday, Mr Mann said that like other scientists, he would rather be in his lab, the field or teaching students. But driving his advocacy are officials who deny his research that shows rising global temperatures.

A marcher in Miami. Picture: Alan Diaz/APSource:AP

In Gainesville, Florida, more than 1,000 people stretched through the city’s streets.

“Most people don’t know how much funding for the sciences supports them in their lives every day. Every medical breakthrough, their food, clothing, our cellphones, our computers, all that is science-based,” said Pati Vitt, a plant scientist at the Chicago Botanic Garden. “So if we stop funding scientific discoveries now, in 10 years, whatever we might have had won’t be, we just won’t have it.”

Protesters in Times Square during the March for Science in New York. Picture: Bryan R. Smith/AFPSource:AFP

At the event in Nashville, Tennessee, where marchers shouted “science, not silence,” lawyer Jatin Shah brought his sons, a five-year-old who wants to be a dentist and six-year-old who plans to be a doctor. Shah worries about the boys’ futures if money is cut for the sciences.

“I fear that we’re not going to have the planet that you and I grew up on unless we find new ways to make this earth as liveable as possible for as long as we can,” Shah said. “And we’re not going to have as intellectual a society as we should. We need as many people as possible to be educated in the sciences.”

People there carried signs that said “there is no planet B,” “make America think again” and “climate change is real, ask any polar bear.”

A protester holds a placard as scientists and science enthusiasts march through central London. Picture: AFPSource:AFP

Marchers in Geneva held signs that said, “Science — A Candle in the Dark” and “Science is the Answer.”

In Berlin, several thousand people participated in a march from one of the city’s universities to the landmark Brandenburg Gate. “’We need to make more of our decisions based on facts again and less on emotions,” said Meike Weltin, a doctorate student at an environmental institute near the capital.

In London, physicists, astronomers, biologists and celebrities gathered for a march past the city’s most celebrated research institutions. Supporters carried signs showing images of a double helix and chemical symbols. In Spain, hundreds assembled in Madrid, Barcelona and Seville.

Thousands of demonstrators attend the demo in Berlin. Picture: Markus Schreiber/APSource:AP

Organisers portrayed the march as political but not partisan, promoting the understanding of science as well as defending it from various attacks, including proposed US government budget cuts under Mr Trump, such as a 20 per cent slice of the National Institute of Health.

Mr Trump’s statement on Saturday said his administration was “committed to advancing scientific research that leads to a better understanding of our environment and of environmental risks.”

The rallies set for more than 500 cities were putting scientists, who generally shy away from advocacy and whose work depends on objective experimentation, into a more public position.

Scientists said they were anxious about political and public rejection of established science such as climate change and the safety of vaccine immunisation.

“Scientists find it appalling that evidence has been crowded out by ideological assertions,” said Rush Holt, a former physicist and Democratic congressman who runs the American Association for the Advancement of Science.

“It is not just about Donald Trump, but there is also no question that marchers are saying ‘when the shoe fits’.”

Judy Twigg, a public health professor at Virginia Commonwealth University, was aiming one of her signs at the president. The sign showed the periodic table of chemical elements and said: “You’re out of your element Donny (Trump).”