BALTIMORE - At a fiery news conference at the Four Seasons hotel here Tuesday, speakers denounced climate change as a hoax perpetrated by a “global cabal” including the United Nations, the World Economic Forum and many leaders of the Catholic Church.

It might have seemed like a fringe event, except for one speaker’s credentials. John F. Clauser shared the Nobel Prize in physics last year before declaring Tuesday that “there is no climate crisis” - a claim that contradicts the overwhelming scientific consensus.

The event showcased Clauser’s remarkable shift since winning one of the world’s most prestigious awards for his groundbreaking experiments with light particles in the 1970s. His recent denial of global warming has alarmed top climate scientists, who warn that he is using his stature to mislead the public about a planetary emergency.

Clauser, 80, who has a booming voice and white hair he often leaves uncombed, has brushed off these concerns. He says skepticism is a key part of the scientific process.

“There was overwhelming consensus that what I was doing was pointless” in the 1970s, he said in an interview after the news conference. “It took 50 years for my work to win the prize. That’s how long it takes for opinions to change.”

Tuesday’s event was organized by the Deposit of Faith Coalition, a group of more than a dozen Catholic organizations that argues that “those pushing the anti-God and anti-family climate agenda need to be called out and exposed.” Clauser, who is an atheist, needed some convincing to be the keynote speaker, a coalition spokesman acknowledged.

The other speakers included Marc Morano, a former Republican congressional staffer who runs a website that rejects mainstream climate science, and Alex Newman, a journalist for right-wing media outlets who has called for exposing the “climate scam.” Both men took multiple jabs at former vice president Al Gore and his 2006 documentary about the dangers of climate change.

Clauser, who wore a gray blazer with black jeans and Teva sandals, appeared buoyant as he took the stage. He cycled through a PowerPoint presentation that began with the exclamation: “Great news! There is no climate crisis!”

“Much as it may upset many people, my message is the planet is not in peril,” Clauser told an audience of roughly a dozen people in the hotel conference room and others watching online. “I call myself a climate denier,” he added. “I’ve been told that’s not politically correct. So I guess I’m a climate crisis d-word person.”

Clauser bragged that he met privately with President Biden in the Oval Office last year, when the 2022 Nobel Prize winners were invited to the White House. He said he criticized Biden’s climate and energy policies, to which he said the president replied: “Sounds like right-wing science.”

The Washington Post could not confirm this account; a White House spokesman did not immediately respond to a request for comment.

The vast majority of climate scientists agree that global warming will have catastrophic consequences for current and future generations. They warn that heat waves, famines and infectious diseases could claim millions of additional lives by century’s end if humanity does not rapidly reduce emissions from the burning of fossil fuels.

The influence of climate deniers has waned over the past several decades, as the science has become clearer and the impacts of global warming have become starker. But a small group of vocal skeptics - including several prominent physicists - has persisted.

Clauser, who has never published a peer-reviewed paper on climate change, has homed in on one message in particular: Earth’s temperature is primarily determined by cloud cover, not carbon dioxide emissions from burning fossil fuels. He has concluded that clouds have a net cooling effect on the planet, so there is no climate crisis.

Michael Mann, a climate scientist at the University of Pennsylvania, said that argument is “pure garbage” and “pseudoscience.”

The “best available evidence” shows that clouds actually have a net warming effect, Mann said in an email. “In physics, we call that a ‘sign error’ - it’s the sort of error a freshman is embarrassed to be caught having made,” he said.

Andrew Dessler, a professor of atmospheric sciences at Texas A&M University, agreed.

“Clouds amplify warming,” Dessler said in an email, adding, “The scientific community has spent the last century studying [climate change] and, at this point, virtually everything that’s happening has been predicted. John Clauser and his ilk ignore this because they are not advancing serious scientific critiques.”

But Anton Zeilinger, an Austrian physicist who shared the Nobel Prize with Clauser last year, said in an interview that he has “very high respect” for Clauser’s scientific rigor, although he cautioned that he is not an expert on climate science.

In 1972, Clauser conducted groundbreaking experiments on quantum entanglement, a process in which two or more particles are coupled so that any change in one particle triggers a simultaneous change in the other, even if they are separated by vast distances. The experiments confirmed a phenomenon that Albert Einstein had famously referred to as “spooky action at a distance.” They also paved the way for technologies such as quantum computers, which can solve problems too complex for classical computers.

“Einstein, when he proposed his ideas, was considered crazy and an outsider,” said Zeilinger, a professor of physics emeritus at the University of Vienna. “It has happened in science that the majority was dead wrong. I have no idea if that is the case here, but science has to be open to debate.”

Some physicists have made crucial contributions to the world’s understanding of climate change. In 2021, the Nobel Prize in physics was awarded to scientists Syukuro Manabe of the United States and Klaus Hasselmann of Germany for work that laid the foundation for current climate models.

Others have made a name for themselves as climate contrarians.

William Happer, a professor emeritus of physics at Princeton University, has argued that global warming is good for humanity. Under President Donald Trump, Happer served as a senior director on the National Security Council, where he oversaw a controversial initiative to reassess the federal government’s analysis of climate science.

Richard Lindzen, a retired MIT physicist, has similarly criticized what he has called “climate alarmism.” And Steven E. Koonin, a physicist who served as the Energy Department’s undersecretary for science under President Barack Obama, wrote the best-selling book “Unsettled: What Climate Science Tells Us, What It Doesn’t, and Why It Matters.”

“There is a skeptical streak in the physics community regarding climate science,” Nadir Jeevanjee, a research physical scientist at the National Oceanic and Atmospheric Administration, wrote in a recent critique of Koonin’s book.

In an interview, Jeevanjee said that while climate science is based in physics, not all physicists are experts in climate science. But that hasn’t stopped some distinguished physicists from portraying themselves as experts and sowing doubt, he said.

“When they talk, people listen,” said Jeevanjee, who emphasized that he was speaking on behalf of himself and not NOAA. “It stokes the flames of denial.”

Some physicists who reject the scientific consensus on climate change have received funding from fossil fuel companies. Wei-Hock “Willie” Soon, an astrophysicist who claims that variations in the sun’s energy have caused most global warming, accepted more than $1.2 million from the fossil fuel industry from 2005 to 2015 while failing to disclose that conflict of interest in most scientific papers.

Clauser said he does not receive any money from oil, gas and coal interests.

“If I go to Asia, I get a huge honorarium for giving talks,” he said in the interview after Tuesday’s event. “But this conference hasn’t given me an honorarium for coming here. The best I get is airfare and hotel. I’m just living off savings.”

In June, Clauser gave the keynote address at a conference on quantum information science in Seoul, telling the audience that “I don’t believe there is a climate crisis.” The speech came a month after he joined the board of directors of the CO2 Coalition, a group that contends carbon dioxide is beneficial for the planet.

Clauser has not been welcomed everywhere. In July, he was scheduled to deliver a seminar on climate models to the International Monetary Fund’s Independent Evaluation Office, but then the event was “summarily canceled” with no explanation, the CO2 Coalition said in a statement at the time.

On Tuesday, Clauser said he was initially told the event would be reformatted as a debate with an author of a report by the U.N. Intergovernmental Panel on Climate Change. But that idea “never went anywhere,” he said.

Asked for comment, a spokesperson for the office declined to comment on the record and did not respond to follow-up questions about whether the event might be rescheduled.

Clauser’s message also may be reaching a limited audience. Of the roughly dozen people at the news conference in Baltimore, two were journalists and several others were members of the Deposit of Faith Coalition.

Asked about the smaller crowd, Clauser, who has emphysema caused by smoking cigarettes in his younger years, took a puff of his inhaler and shrugged.

“I get a reasonable amount of fan mail, some of which comes from people who claim to be climate scientists,” he said. “Most of it is very positive.”