As natural disasters and extreme environmental conditions became more commonplace around the world this summer, scientists pointed repeatedly to a shared driver: climate change.

Conspiracy theorists pointed to anything but.

Some claimed falsely that the record-smashing heat waves blistering parts of North America, Europe and Asia were normal, and that they had been sensationalized as part of a globalist hoax. Others made up tales that cloud-seeding airplanes or a nearby dam, rather than torrential rains, had caused the unusually intense flooding in northern Italy (and in places like Vermont and Rwanda).

The devastating wildfire on Maui this month produced especially ludicrous claims. Social media that racked up millions of views blamed the blaze on a “directed energy weapon” (the evidence: years-old footage not recorded in Hawaii). And as Florida braced this week for Hurricane Idalia, some people claimed incorrectly online that such storms are not affected by fossil fuel emissions.

The unfounded claims that now regularly follow natural disasters and dangerous weather, contradicting a preponderance of scientific evidence, can often seem frivolous and fantastical. They persist, however — attracting large audiences and frustrating climate experts, who say the world has little time to evade a global warming catastrophe.

The claims can start with blog posts paid for by the oil and gas industry, or from rumors shared among neighbors. Online forums are filled with comments in multiple languages that reject both the science behind fossil fuel emissions and the scientists’ authority. Sometimes, they are amplified by top politicians and pundits — the Republican presidential candidate Vivek Ramaswamy, for example, called climate change a “hoax” during the first primary debate last week.

“It’s really one of the worst challenges we have to deal with,” said Eleni Myrivili, the chief heat officer for the United Nations human settlements program.

After holding a similar role for the city of Athens, which was threatened by a ruinous spate of wildfires this month, Dr. Myrivili said climate misinformation was “one of the most painful things because it’s like adding insult to injury.”

Outright climate deniers are a minority: 74 percent of Americans believe global warming is happening, versus 15 percent who do not, according to a survey conducted in the spring by the Yale Program on Climate Change Communication and the George Mason University Center for Climate Change Communication. However, while 61 percent understand that humans are mostly at fault — the consensus of nearly all of the scientific community — 28 percent say the phenomenon is a largely natural evolution.

Experts said the tactics and tenor of climate denial had evolved. For decades, the oil and gas industry spent billions of dollars waging a coordinated and highly technical campaign to influence public opinion against climate science, and then climate action. Recently, conspiracy theorists and extremists have operated in a more decentralized way, generating revenue through deceptive clickbait about global warming.

“Those two universes of actors have collided with each other in the online space and basically found a marriage of convenience,” said Jennie King, head of climate research and policy at the Institute for Strategic Dialogue, a think tank that studies online platforms. “You have the informal and the formal, the traditional and the very digital now occupying the same ecosystem and ramping it up to new extremes.”

The consequences from global warming are complex. Natural disasters and extreme weather events would still occur without it, albeit on a smaller scale, for example. That helps fuel many false narratives, said Susannah Crockford, an environmental anthropologist at the University of Exeter in England.

Dr. Crockford, who studies climate denial, said she was sympathetic to the urge to concoct explanations that shifted responsibility away from climate change toward a boogeyman like arsonists or “the elite.”

“Blaming a specific enemy makes it easier to fight — you just have to get rid of the bad people that are making this happen, and then the problem goes away,” Dr. Crockford said.

Climate Action Against Disinformation, a coalition of dozens of groups combating false narratives, analyzed claims about wildfires over the past three years. In a report last month, the organization demonstrated how such claims are recycled and adapted for the zeitgeist. The Black Lives Matter movement and antifa protesters were scapegoats when wildfires erupted in California, Oregon and Washington in 2020. By the time Canada faced its own wildfires this summer, Prime Minister Justin Trudeau was being baselessly linked to eco-terrorist activity.

In Maui, fears that predatory developers would swoop in after the fire quickly warped into unsupported claims that wealthy real estate investors had caused the blaze. Video of Hawaii’s governor saying the state might acquire land in Lahaina to protect it for locals was manipulated and offered as misleading proof that his plan was to buy land to create a technologically advanced “smart city.”

One YouTube video shared unfounded claims that Oprah Winfrey had a hand in starting the inferno on the island, hoping to seize land from Indigenous residents. As proof, the video’s host noted that Ms. Winfrey had recently bought a sizable plot on Maui (she has lived part time on the island for 15 years) and that her holdings had escaped this month’s inferno (her home was miles away from the closest blaze). The host added another supposed red flag: In one interview about the fire, Ms. Winfrey failed to appear sufficiently sad.

Ms. Winfrey did not respond to a request for comment.

County officials in Maui had warned for years about the risk of climate change causing more frequent and intense wildfires. Experts later suggested that the Lahaina blaze had been stoked by worsening drought conditions, low humidity and gales linked to a hurricane hundreds of miles away.

Global warming, however, did not factor into the false theories that surged through social media. One TikTok user said that “some people caught pictures of the lasers coming down and starting the fire on Maui.” As evidence, she shared two images: one from the SpaceX Instagram account showing the company’s Falcon 9 rocket launching from California in 2018, the other from a five-year-old photo posted to Facebook after a controlled flare from an oil refinery in Ohio. (Other images claiming to capture a “direct energy weapon” at work in Maui show transformer explosions in Chile and Louisiana.)

Climate activists are concerned that social platforms and technology like artificial intelligence will help produce and hasten the spread of misinformation about natural disasters and extreme weather.

This year, researchers found ads from retailers, electronics manufacturers and airlines accompanying YouTube videos that falsely claimed that the rainforest was too humid to catch fire or that the world was cooling. (YouTube has said it removes ads from videos denying climate change.) A report this month from Pomona College found that, within six months of Elon Musk’s taking over Twitter, nearly half of users who had regularly discussed the environment were no longer active.

Scientists and other climate change experts are being besieged by personal attacks, including claims that they are shills for a globalist cabal or other shadowy forces, said Ms. King of the Institute for Strategic Dialogue. Eroding trust in experts traps everyone in an “antechamber of discussion,” bickering about credibility rather than taking action.

“The danger is not that people hold unpalatable views in and of themselves,” she said. “It’s more our inability to have a good-faith conversation about these absolutely critical issues in the years ahead.”