Thousands of scientists worldwide left their labs to take to the streets on Saturday along with students and research advocates in a push back against what they say are mounting attacks on science.
The March for Science, coinciding with Earth Day, took place in about 600 cities.
It was an event intended to promote the understanding of science and defend the discipline from proposed government budget cuts and threats to global agreements such as the Paris Agreement on climate change.
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.
Marchers in Geneva carried signs that said, "Science - A Candle in the Dark" and "Science is the Answer."
In Berlin, several thousand people participated in a march from the one of the city's universities to the Brandenburg Gate. "We need to make more of our decision based on facts again and less on emotions," said Meike Weltin, a doctorate student at an environmental institute near the capital.
The protest put scientists, who generally shy away from advocacy and whose work depends on objective experimentation, into a more public position.
Signs and banners at the Washington, DC, rally reflected anger, humour and obscure scientific references, such as a seven-year-old's "No Taxation Without Taxonomy." Taxonomy is the science of classifying animals, plants and other organisms.
On a more serious side, Pam Haddad, a social worker from Pennsylvania, said science saved her life.
"I think it's been made clear by the government that they want to make a lot of cutting of science funding. Cancer research saved my life five years ago," Haddad told Al Jazeera.
"It's important to show solidarity. If one person shows up, no one pays attention. But if we all come, they can't ignore us."
|Pam Haddad [Cajsa Wikstrom/Al Jazeera]|
Scientists involved in the march said they were anxious about political and public rejection of established science such as climate change and the safety of vaccine immunisations.
Speakers in Washington included Bill Nye, a TV personality known as "the Science Guy", and Mona Hanna-Attisha, a pediatrician and public health campaigner who first called attention to the high levels of lead in the drinking water of Flint, Michigan.
"Flint is what happens when we dismiss science," she said, referring to the 2014 crisis.
US President Donald Trump has vowed to slash budgets for research at top US agencies, including the National Institutes of Health (NIH), NASA, the National Oceanic and Atmospheric Administration, and the Environmental Protection Agency (EPA).
Trump's head of the EPA, Scott Pruitt, claimed last month that carbon dioxide is not the main driver of global warming, a position starkly at odds with the international scientific consensus on the matter.
Nipa Shah, a physician, told Al Jazeera that budget cuts to science agencies were troubling.
"I think it's very important to stand up for science and that the current political climate is worrisome with cuts to NIH, cuts to EPA, things that I think are really important. I'm a physician and I think vaccines are important, I think research is important, and I just want to make a stand. I think every little bit counts," said Shah.
|Dr Nipa Shah [Cajsa Wikstrom/Al Jazeera]|
Trump said in an Earth Day statement his administration is "committed to keeping our air and water clean, to preserving our forests, lakes and open spaces and to protecting endangered species".
But that won't be done in a way that harms "working families", he said.
The US government is "reducing unnecessary burdens on American workers and American companies, while being mindful that our actions must also protect the environment", Trump added.
Library curator Micah Messenheimer said it was "scary" what the politicians are up to. "I believe in facts and I think we're in a country and a situation where that's not a given any more," he told Al Jazeera.
"We have a president and Congress who dismiss scientific facts and things like climate change. They're not passing legislation to improve the environment, they're making things worse. By disbelieving in facts we create a situation where it's hard to have anything that's real. We're in a political situation where lying has become the prevalent mode of acting."
|Micah Messenheimer [Cajsa Wikstrom/Al Jazeera]|
Stephanie Groleau is marine safety engineer for the US Coast Guard. She said it's not only the politicians but the media that is to blame for the lack of respect for scientific reason.
"One of the things that bothers me right now is that most Americans don't really understand what a scientific consensus is and the media is not helping. For example with climate change, there's a scientific consensus - 99 percent of scientists agree that climate change is real, 1 percent doesn't.
"But the media, in order to try and appear neutral, will have one person represent 'climate change is real' and one person represent 'climate change is not real'," Groleau told Al Jazeera.
"So when regular Americans are watching that on TV, they think it's a 50-50. When facts are being discussed, not opinions, it's not 50-50."
|Stephanie Groleau [Cajsa Wikstrom/Al Jazeera]|
Source: Al Jazeera and news agencies