They believe human actions are changing the environment. They believe we need to take urgent action to save the planet for future generations. So why do so many chemtrail conspiracy theorists think climate change is a big hoax?

For weeks, attacks on teenage climate activist Greta Thunberg have been the most popular posts on the most popular Facebook page for the chemtrail conspiracy theory. At nearly 183,000 members, the page is a stronghold for people who believe the government or other agencies are spraying chemicals out of planes for nefarious purposes (perhaps mind control, perhaps weather control, depending on which believer you ask). And as Thunberg and American school children rally for climate action, they’re becoming a favorite target of the conspiracy crowd.

Thunberg, a 16-year-old Swedish climate activist, is the most visible young person demanding environmental action from world leaders. Late last month, she addressed the United Nations in a fiery speech that drew scorn from the right—notably President Donald Trump and Russian President Vladimir Putin.

Trump retweeted a post calling the high schooler an “actress” who was “getting the best education socialism can steal,” but the comments on conspiracy Facebook pages were far more vitriolic. After weeks of photoshops likening Thunberg to Hitler and worse, some members of the largest chemtrail group thought it had gone too far.

“Admin - if you continue to let people troll Greta on here you’re a gutless swine,” one user, who typically posts chemtrail theories wrote on the page last week. The page’s administrator hit back in a long post accusing Thunberg of being part of a New World Order plot to “lead us all to literal slavery.” The Hitler photoshops resumed in the comments section.

Despite their shared interest in the weather, chemtrail believers and climate activists have little common ground. That, according to Peter Ditto, a professor of psychological science studying motivated reasoning at the University of California Irvine, can be chalked up to conservative politics

Ditto said climate denialism often functions “like a team sport.” Although there’s no moral argument against accepting climate data, “for other reasons, probably economic, the Republican party and conservative thinkers have decided they don’t want to believe [climate change], that it’s threatening to them,” Ditto said. “There’s such a team, tribal mentality in the United States right now that people just line up and say, ‘My side doesn’t believe that… believing that is almost tantamount to treason, or betrayal.’”

Some chemtrail believers incorporate more left-leaning fears, like suspicion of agricultural giant Monsanto, into their thinking. But Facebook groups for the movement show a prevailing and growing alignment with the right. (The chemtrail theory has considerable overlap with the anti-vaccination movement, which has flourished in some liberal enclaves but also has a growing fanbase on the far right.)

“Climate change denialism is a huge feature of conspiracy theories, especially on the right (but not exclusively),” said Anna Merlan, author of Republic of Lies: American Conspiracy Theorists and Their Surprising Rise to Power. “It ties in neatly with a suspicion of world governments and ‘official stories’ and especially distrust of anything that calls for worldwide solutions, like the Paris agreement.”

The United Nations, where Thunberg spoke last month, is a popular demon in conspiracy circles, especially when it comes to environmental policy. In 1992, the U.N. passed Agenda 21, a nonbinding environmental agreement that found a foe in American right-wing and anti-environmental interests from the start. Members of conspiratorial groups like the John Birch Society suggested the environmental guidelines were actually a U.N. plot to chip away at American independence. Those fears trickled up through the right, bursting into the mainstream in 2012 when conservative pundit Glenn Beck wrote a dystopian novel called Agenda 21 and the GOP officially adopted a resolution condemning Agenda 21 as “erosive of American sovereignty.” (The chemtrail group admin cited Agenda 21 in his post justifying attacks on Thunberg.)

Young climate activists stand at an unfortunate meeting point of conspiracy theories. Asking world leaders for climate solutions gets them branded as puppets in a New World Order scheme. And even pointing out the reality of climate change puts them at odds with an evolving set of conspiracy theorists and figures on the right.

“Climate denialism is an older idea that's constantly seeing new updates,” Merlan said. “Rush Limbaugh has been shouting about global warming being a lie for years and years, and Alex Jones has been a longtime skeptic too, but I constantly see new conspiracy communities tying into it, like QAnon, since it fits their other political viewpoints.”

Among those newer conspiracy communities is Natural News, a site that began as a hub for organic food junkies but morphed into an Infowars-on-ketamine conspiracy site over the past decade. Despite the site’s purported love of nature, it regularly denounces climate change as a hoax. (Two of its top headlines on Thursday: “NASA admits that climate change occurs because of changes in Earth’s solar orbit, and NOT because of SUVs and fossil fuels” and “Climate change hoax COLLAPSES as new science finds human activity has virtually zero impact on global temperatures.”)

Climate denial (and lately, anti-Thunberg memes) also crops up among the Flat Earth community, which believes the planet is a flat disc, probably covered by a dome. For some Flat Earthers, climate denial is part of a cohesive worldview that claims most of the world’s ills are actually hoaxes. This set of Flat Earthers claim that the people involved in covering up Earth’s true pizza-like shape are also lying about climate change and the existence of free, unlimited energy. It doesn’t help that climate change is sometimes called “global warming.”

Like chemtrail believers, Flat Earthers often take a keen interest in the environment. But they interpret climate data in a way that supports their theory. When news outlets reported about the breakoff of a massive Antarctic ice shelf this week, Flat Earthers eagerly shared the story because its picture of a sheer cliff of ice looks like the ice wall that many Flat Earthers believe surrounds the flat planet.

Not all Flat Earthers believe climate change is a hoax, however. Last July, the Flat Earth Society tweeted that “it would be nothing short of irresponsible to question something with so much overwhelming evidence behind it, and something that threatens us so directly as a species.”

Conspiracy theorists aren’t the only ones reluctant to accept data that challenges their beliefs. We’re all guilty of it, to a degree, Ditto said.

“When people get information that challenges them, they tend to take it harder. It’s an idea I call motivated skepticism,” he said. “People are more skeptical of information they want to believe than information they do, so they have harder standards for things that challenge their political beliefs. That’s a very fundamental phenomenon.”

Conspiracy theorizing is a different mental process, he said. “People look for patterns, see patterns and data that aren’t there.”

Merlan noted that conspiracy theories can also act as a balm for people faced with a complicated problem like climate change. “Climate change denialists functionally preach that we all just need to ignore scientists, experts and activists—or maybe accuse them of being globalist tools or brainwashed by a Satanic Cabal—and do absolutely nothing else,” she said.

In that sense, the attacks on Thunberg mirror last year’s attacks on teenagers who rallied for new gun legislation following a massacre at Parkland, Florida’s Marjory Stoneman Douglas High School. Some conspiracy theorists accused the teenage survivors of being involved in a Deep State plot to seize their guns. Others claimed the shooting never happened at all.

“It's like false flag conspiracy theories about gun control in that way,” Merlan said of climate denialists, “and like those, it encourages inaction and apathy at the worst possible time for it.”