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Tennessee lawmakers have passed a bill banning the release of airborne chemicals that critics say is inspired by "chemtrails" conspiracy theories.
The bill forbids "intentional injection, release, or dispersion" of chemicals into the air.
It doesn't explicitly mention chemtrails, which conspiracy theorists believe are poisons spread by planes.
Instead it broadly prohibits "affecting temperature, weather, or the intensity of the sunlight".
The Republican-sponsored bill passed along party lines on Monday. If it is signed by Tennessee's governor, Republican Bill Lee, it will go into effect on 1 July.
The bill's backers were spurred on by a government report released last year on solar geoengineering, which is the idea of cooling the planet by reflecting sunlight back into space. The White House, though, has said that there are no plans "to establish a comprehensive research program focused on solar radiation modification."
Several witnesses who testified before the Tennessee legislature cited debunked conspiracy theories or speculated about secret government geoengineering programmes, according to Scott Banbury, conservation director of the state's branch of the Sierra Club, an environmental organisation.
Their claims were troubling, he said.
"As a serious environmental organisation, if what was in the bill was actually going on we would be calling for a stop to it," he said. "It's not happening."
Geoengineering, weather modification and 'chemtrails'
The legislation focuses on geoengineering, a very broad category which includes mostly theoretical large-scale action to mitigate climate change.
Geoengineering is controversial even among legitimate climate scientists, because of uncertainty around its usefulness and the possibility of unintended outcomes.
Planet-wide climate engineering is distinct from more routine weather modification, such as cloud seeding, which increases rainfall over specific areas and is used in several US states.
"Chemtrails", meanwhile, is a separate, pseudoscientific idea that governments or corporations are spraying chemicals from planes to kill, control or poison people.
Conspiracy theorists point to white plumes of water vapour trailing behind passenger airplanes, commonly called contrails, as proof of sinister and secret plots, but lack evidence for their claims.
The most common claim of proof is "simply that aircraft contrails look 'different', without any comparative analysis," according to a report from a Harvard geoengineering group.
"This as convincing as saying that alien beings walk among us in disguise as people because some people act very strangely," it said.
In recent decades speculation about chemtrails has risen as the number of airline flights - and thus the number of contrails - has surged.
In the debate over the Tennessee bill, lawmakers and witnesses cited a range of both reliable and debunked facts about geoengineering and weather modification, and at least one witness said she believed the White House was engaged in climate experiments but could not provide definitive proof.
The legislation's sponsor, Monty Fritts, called it "a very common-sense thing to do".
Although several lawmakers mentioned chemtrails while the bill was being discussed, during Monday's session Mr Fritts focused on cloud seeding.
"Everything that goes up must come down, and those chemicals that we knowingly and willingly inject into the atmosphere simply to control the weather or the climate are affecting our health," he said.
In a joking response, John Ray Clemmons, a Democrat from Nashville, introduced an amendment that would protect fictional beasts.
"This amendment would make sure that we are protecting yetis, or Sasquatch or Bigfoot, from whatever this conspiracy is that we're passing in this legislation," he said during debate.
"This legislation is not to be taken seriously," he said.
Mr Clemmons told the BBC that several of his fellow lawmakers believe in QAnon theories and conspiracies about vaccines being hidden in food.
"This is unfortunately nothing new," he said. "There's a lot of things we could be doing to reduce living costs for our working families, but we are wasting time with this."
A spokesperson for Mr Fritts said: "Nothing that helps ensure that our air, water, and soil are cleaner could be a waste of time."
"We cannot change what people believe," the spokesperson said about the persistent conspiracy theory allegations. "We can only present the information and let them make up their own minds."
The BBC contacted Governor Lee's office for comment.
Although the Tennessee bill appears to be the first of its kind to pass a state legislature, lawmakers in several other states including Pennsylvania, Rhode Island, Kentucky, Minnesota and New Hampshire have introduced similar legislation.
Mr Banbury, the Sierra Club official, noted that witnesses supporting the bill travelled from outside Tennessee, and several have testified in favour of similar laws in other states.
"As a grassroots organizer I'm impressed that a cadre of the same people have had such influence, and that they can muster up so much power," he said.