Chemtrail conspiracy theory

The chemtrail conspiracy theory posits the erroneous[1] belief that long-lasting condensation trails are "chemtrails" consisting of chemical or biological agents left in the sky by high-flying aircraft, sprayed for nefarious purposes undisclosed to the general public.[2] Believers in this conspiracy theory say that while normal contrails dissipate relatively quickly, contrails that linger must contain additional substances.[3][4] Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management,[3] weather modification, psychological manipulation, human population control, biological or chemical warfare, or testing of biological or chemical agents on a population, and that the trails are causing respiratory illnesses and other health problems.[2][5]

This article is about the conspiracy theory that contrails are deliberate releases of poison. For harmful chemicals emitted by aircraft, see Environmental impact of aviation. For attempts to influence weather with aircraft, see Cloud seeding. For the use of aircraft to apply pesticide and herbicide, see Crop dusting. For the Beck song, see Chemtrails (song).

An Airbus A340's engines leaving a water condensation trail (contrail) – miniature clouds formed by the engine exhaust

The claim has been dismissed by the scientific community. There is no evidence that purported chemtrails differ from normal water-based contrails routinely left by high-flying aircraft under certain atmospheric conditions.[6] Although proponents have tried to prove that chemical spraying occurs, their analyses have been flawed or based on misconceptions.[7][8] Because of the persistence of the conspiracy theory and questions about government involvement, scientists and government agencies around the world have repeatedly explained that the supposed chemtrails are in fact normal contrails.[3][9][10]

The term chemtrail is a portmanteau of the words chemical and trail, just as contrail is a portmanteau of condensation and trail.[11]

History
Multiple concurrent contrails. How long they last depends upon the weather, especially the temperature, humidity, and wind speed.

Chemtrail conspiracy theories began to circulate after the United States Air Force (USAF) published a 1996 report about weather modification.[10] Following the report, in the late 1990s the USAF was accused of "spraying the U.S. population with mysterious substances" from aircraft "generating unusual contrail patterns."[6][12] The theories were posted on Internet forums by people including Richard Finke and William Thomas, and were among many conspiracy theories popularized by late-night radio host Art Bell, starting in 1999.[13][8] As the chemtrail conspiracy theory spread, federal officials were flooded with angry calls and letters.[10][3]

A multi-agency response attempting to dispel the rumors was published in 2000 by the Environmental Protection Agency (EPA), the Federal Aviation Administration (FAA), the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA).[14][15] Many chemtrail believers interpreted agency fact sheets as further evidence of the existence of a government cover-up.[3] The EPA refreshed its posting in 2015.[16]

In the early 2000s the USAF released an undated fact sheet that stated the conspiracy theories were a hoax fueled in part by citations to a 1996 strategy paper drafted within their Air University titled Weather as a Force Multiplier: Owning the Weather in 2025.[17][18] The paper was presented in response to a military directive to outline a future strategic weather modification system for the purpose of maintaining the United States' military dominance in the year 2025, and identified as "fictional representations of future situations/scenarios."[18] The USAF further clarified in 2005 that the paper "does not reflect current military policy, practice, or capability," and that it is "not conducting any weather modification experiments or programs and has no plans to do so in the future."[6][19] Additionally, the USAF states that the "'Chemtrail' hoax has been investigated and refuted by many established and accredited universities, scientific organizations, and major media publications."[6]

The conspiracy theories are seldom covered by the mainstream media, and when they are, they are usually cast as an example of anti-government paranoia.[4] For example, in 2013, when it was made public that the CIA, NASA, and NOAA intended to provide funds to the National Academy of Sciences to conduct research into methods to counteract global warming with geoengineering, an article in the International Business Times anticipated that "the idea of any government agency looking at ways to control, or manipulate, the weather will be met with scrutiny and fears of a malign conspiracies" [sic], and mentioned chemtrail conspiracy theories as an example.[20]

Description

Proponents of the chemtrail conspiracy theory find support for their theories in their interpretations of sky phenomena, videos posted to the internet, and reports about government programs; they also have certain beliefs about the goals of the alleged conspiracy and the effects of its alleged efforts and generally take certain actions based on those beliefs.

Interpretation of evidence
Airbus A380 water-filled tanks simulate passenger weight for different takeoff and landing displacement weights. Similar photographs are sometimes said to show chemtrail planes in action
Ballast barrels with water in a prototype Boeing 747 flight-test plane

Proponents of the chemtrail conspiracy theory say that chemtrails can be distinguished from contrails by their long duration, asserting that the chemtrails are those trails left by aircraft that persist for as much as a half-day or transform into cirrus-like clouds.[4] The proponents claim that after 1995 contrails had a different chemical composition and lasted a lot longer on the sky; proponents fail to acknowledge evidence of long-lasting contrails shown in World War II–era photographs.[8]

Proponents characterize contrails as streams that persist for hours and that, with their criss-cross, grid-like or parallel stripe patterns, eventually blend to form large clouds. Proponents view the presence of visible color spectra in the streams, unusual concentrations of sky tracks in a single area, or lingering tracks left by unmarked or military airplanes flying at atypical altitudes or locations as markers of chemtrails.[3][5][21][22][23]

Photographs of barrels installed in the passenger space of an aircraft for flight test purposes have been claimed to show aerosol dispersion systems. The real purpose of the barrels is to simulate the weight of passengers or cargo. The barrels are filled with water, and the water can be pumped from barrel to barrel in order to test different centers of gravity while the aircraft is in flight.[24]

Former CIA employee and whistleblower Edward Snowden, interviewed on "The Joe Rogan Experience", stated that he had searched through all the secret information of the US government for evidence about (aliens and) chemtrails. According to a CNN report[25] about the webcast[26] he said: "In case you were wondering: ... Chemtrails are not a thing," and: "I had ridiculous access to the networks of the NSA, the CIA, the military, all these groups. I couldn't find anything"

Jim Marrs has cited a 2007 Louisiana television station report as evidence for chemtrails. In the report the air underneath a crosshatch of supposed chemtrails was measured and apparently found to contain unsafe levels of barium: at 6.8 parts per million, three times the US nationally recommended limit. A subsequent analysis of the footage showed, however, that the equipment had been misused, and the reading exaggerated by a factor of 100—the true level of barium measured was both usual and safe.[7]

In May 2014 a video that went viral showed a commercial passenger airplane landing on a foggy night, which was described as emitting chemtrails.[27] Discovery News pointed out that passengers sitting behind the wings would clearly see anything being sprayed, which would defeat any intent to be secretive, and that the purported chemical emission was normal air disruption caused by the wings, visible due to the fog.[27] In October 2014, Englishman Chris Bovey filmed a video of a plane jettisoning fuel on a flight from Buenos Aires to London, which had to dump fuel to lighten its load for an emergency landing in São Paulo. The clip went viral on Facebook, with over three million views and more than 52,000 shares, cited as evidence of chemtrails. He later disclosed that the video post was done as a prank, and consequently, he was subjected to some vitriolic abuse and threats from several conspiracy believers.[28][29]

In some accounts, the chemicals are described as barium and aluminum salts, polymer fibers, thorium, or silicon carbide.[30]

Chemtrail believers interpret the existence of cloud seeding programs and research into climate engineering as evidence for the conspiracy.[31]

Beliefs

Various versions of the chemtrail conspiracy theory have been propagated via the Internet and radio programs.[3] There are websites dedicated to the conspiracy theory, and it is particularly favored by far right groups because it fits well with deep suspicion of government.[4]

A 2014 review of 20 chemtrail websites found that believers appeal to science in some of their arguments, but do not believe what academic or government-employed scientists say;[30] scientists and federal agencies have consistently denied that chemtrails exist, explaining the sky tracks are simply persistent contrails.[3][12][32] The review also found that believers generally hold that chemtrails are evidence of a global conspiracy; they allege various goals which include profit (for example, manipulating futures prices, or making people sick to benefit drug companies), population control, or weapons testing (use of weather as a weapon, or testing bioweapons).[30][32][2] One of these ideas is that clouds are being seeded with electrically conductive materials as part of a massive electromagnetic superweapons program based around the High Frequency Active Auroral Research Program (HAARP).[33][34] Believers say chemtrails are toxic; the 2014 review found that they generally hold that every person is under attack and often express fear, anxiety, sadness, and anger about this.[30] A 2011 study of people from the US, Canada, and the UK found that 2.6% of the sample believed entirely in the conspiracy theory, and 14% believed it partially.[35][30] An analysis of responses given to the 2016 Cooperative Congressional Election Study showed that 9% of the 36,000 respondents believed it was "completely true" that "...the government has a secret program that uses airplanes to put harmful chemicals into the air..." while a further 19% believed this was "somewhat true".[36]

Actions

Chemtrail conspiracy theorists often describe their experience as being akin to a religious conversion experience. When they "wake up" and become "aware" of chemtrails, the experience motivates them to advocacy of various forms.[30] For example, they often attend events and conferences on geoengineering, and have sent threats to academics working in the geoengineering field.[30]

In 2001 in response to requests from constituents, US Congressman Dennis Kucinich introduced (but did not author) H.R. 2977 (107th), the Space Preservation Act of 2001 that would have permanently prohibited the basing of weapons in space, listing chemtrails as one of a number of "exotic weapons" that would be banned.[37][38] Proponents have interpreted this explicit reference to chemtrails as official government acknowledgment of their existence.[21][39] Skeptics note that the bill in question also mentions "extraterrestrial weapons" and "environmental, climate, or tectonic weapons."[37] The bill received an unfavorable evaluation from the United States Department of Defense and died in committee, with no mention of chemtrails appearing in the text of any of the three subsequent failed attempts by Kucinich to enact a Space Preservation Act.

In 2003, in a response to a petition by concerned Canadian citizens regarding "chemicals used in aerial sprayings are adversely affecting the health of Canadians," the Government House Leader responded by stating, "There is no substantiated evidence, scientific or otherwise, to support the allegation that there is high altitude spraying conducted in Canadian airspace. The term 'chemtrails' is a popularised expression, and there is no scientific evidence to support their existence."[40][41][42][43] The house leader went on to say that "it is our belief that the petitioners are seeing regular airplane condensation trails, or contrails."[40]

In the United Kingdom, in 2005 Elliot Morley, a Minister of State for the Department for Environment, Food and Rural Affairs[44] was asked by David Drew, the Labour Party Member of Parliament for Stroud, "what research [the] Department has undertaken into the polluting effects of chemtrails for aircraft," and responded that "the Department is not researching into chemtrails from aircraft as they are not scientifically recognised phenomena," and that work was being conducted to understand "how contrails are formed and what effects they have on the atmosphere."[12][45]

Some chemtrail believers adopt the notions of Wilhelm Reich (1897–1957) who devised a "cloudbuster" device from pipework. Reich claimed this device would influence weather and remove harmful energy from the atmosphere. Some chemtrail believers have built cloudbusters filled with crystals and metal filings, which are pointed at the sky in an attempt to clear it of chemtrails.[46]

Chemtrail believers sometimes gather samples and have them tested, rather than rely on reports from government or academic laboratories, but their experiments are usually flawed; for example collecting samples in jars with metal lids contaminates the sample and is not done in scientific testing.[30][47]

Contrails
Main article: Contrail
Contrails from propeller-driven aircraft engine exhaust, early 1940s

Contrails, or condensation trails, are "streaks of condensed water vapor created in the air by an airplane or rocket at high altitudes."[6] Fossil fuel combustion (as in piston and jet engines) produces carbon dioxide and water vapor. At high altitudes the air is very cold. Hot humid air from the engine exhaust mixes with the colder surrounding air, causing the water vapor to condense into droplets or ice crystals that form visible clouds. The rate at which contrails dissipate is entirely dependent on weather conditions. If the atmosphere is near saturation, the contrail may exist for some time. Conversely, if the atmosphere is dry, the contrail will dissipate quickly.[6]

Exhaust gases and emissions
Wingtip condensation trails

It is well established by atmospheric scientists that contrails can persist for hours, and that it is normal for them to spread out into cirrus sheets. The different-sized ice crystals in contrails descend at different rates, which spreads the contrail vertically. Then the differential in wind speeds between altitudes (wind shear) results in horizontal spreading of the contrail. This mechanism is similar to the formation of cirrus uncinus clouds. Contrails between 25,000 and 40,000 feet (7,600 and 12,200 m) can often merge into an "almost solid" interlaced sheet.[48] Contrails can have a lateral spread of several kilometers, and given sufficient air traffic, it is possible for contrails to create an entirely overcast sky that increases the ice budget of individual contrails and persists for hours.[49]

Contrail testing being carried out on an Airbus A340 and much older Boeing 707[6]

Experts on atmospheric phenomena say that the characteristics attributed to chemtrails are simply features of contrails responding to diverse conditions in terms of sunlight, temperature, horizontal and vertical wind shear, and humidity levels present at the aircraft's altitude.[3][6][5][21] In the US, the gridlike nature of the National Airspace System's flight lanes tends to cause crosshatched contrails, and in general it is hard to discern from the ground whether overlapping contrails are at similar altitudes or not.[6] The jointly published fact sheet produced by NASA, the EPA, the FAA, and NOAA in 2000 in response to alarms over chemtrails details the science of contrail formation, and outlines both the known and potential impacts contrails have on temperature and climate.[19] The USAF produced a fact sheet that described these contrail phenomena as observed and analyzed since at least 1953. It also rebutted chemtrail theories more directly by identifying the theories as a hoax and disproving the existence of chemtrails.[6][3]

Patrick Minnis, an atmospheric scientist with NASA's Langley Research Center in Hampton, Virginia, has said that logic does not dissuade most chemtrail proponents: "If you try to pin these people down and refute things, it's, 'Well, you're just part of the conspiracy'," he said.[3]

Analysis of the use of commercial aircraft tracks for climate engineering has shown them to be generally unsuitable.[50]

Astronomer Bob Berman has characterized the chemtrail conspiracy theory as a classic example of failure to apply Occam's razor, writing in 2009 that instead of adopting the long-established "simple solution" that the trails consist of frozen water vapour, "the conspiracy web sites think the phenomenon started only a decade ago and involves an evil scheme in which 40,000 commercial pilots and air traffic controllers are in on the plot to poison their own children."[51]

A 2016 survey of 77 atmospheric scientists concluded that "76 out of 77 (98.7%) of scientists that took part in this study said there was no evidence of a [secret large-scale atmospheric program] (SLAP), and that the data cited as evidence could be explained through other factors, such as typical contrail formation and poor data sampling instructions presented on SLAP websites."[52][53]

See also

References
  1. Science, Carnegie (12 August 2016). ""Chemtrails" not real, say leading atmospheric science experts". Carnegie Institution for Science. Retrieved 11 May 2019. Some groups and individuals erroneously believe that the long-lasting condensation trails, or contrails, left behind aircraft are evidence of a secret large-scale spraying program. They call these imagined features "chemtrails".
  2. Fraser, Stephen (2009). "Phantom menace? Are conspirators using aircraft to pollute the sky?". Current Science. 94 (14): 8–9. ProQuest 195877531. Some theorists speculate that the goal is population control; some say it's climate modification; others say it's military weapons testing. (subscription required)
  3. Watson, Traci (7 March 2001). "Conspiracy theorists read between lines in the sky". USA Today. p. A.04. Exasperated by persistent questions, the Environmental Protection Agency, NASA, the Federal Aviation Administration and the National Oceanic and Atmospheric Administration joined forces last fall to publish a fact sheet explaining the science of contrail formation. A few months earlier, the Air Force had put out its own fact sheet, which tries to refute its opponents' arguments point by point. "If you try to pin these people down and refute things, it's, 'Well, you're just part of the conspiracy,' " says atmospheric scientist Patrick Minnis of NASA's Langley Research Center in Hampton, Va. "Logic is not exactly a real selling point for most of them."
  4. James, Nigel (2003). "Contrails". In Knight, Peter (ed.). Conspiracy Theories in American History: An Encyclopedia. ABC-CLIO. pp. 197–199. ISBN 978-1-57607-812-9. there are no books on the subject to date. Reports on contrails are carried by dedicated websites...Mainstream news agencies rarely report on concerns over contrails, and when they do it is in terms of anti-government "paranoia". When USA Today ran a contrail story it likened the story to something out of The X-Files, arguing that it was only those who are suspicious of the government who believe that lines in the sky are evidence of malfeasance. Some suggested that they are trying to slow down global warming with compounds that reflect sunlight into the sky.
  5. Schlatter, Thomas (9 March 2001). "Weather Queries: Chemtrail Controversy". Weatherwise. Archived from the original on 9 March 2001.
  6. "Contrails Facts" (PDF). US Air Force. 13 October 2005. Archived from the original (PDF) on 6 March 2013.
  7. Radford, Benjamin (March–April 2009). "Curious contrails: death from the sky?". Skeptical Inquirer. 33 (2): 25.
  8. Kreidler, Marc (1 September 2008). "The 'Chemtrail Conspiracy'". Skeptical Inquirer. 18 (3). ISSN 0194-6730. OCLC 819017418. Retrieved 6 May 2020.
  9. Cama, Timothy (13 March 2015). "EPA confronts 'chemtrails' conspiracy talk". the Hill. Retrieved 10 December 2016. Conspiracy theorists say that government officials or others are using jets to spray harmful chemicals into the atmosphere. They cite the contrails left by jets as evidence of the chemicals. The EPA has added a new notice to its website, which links to a fact sheet explaining that the trails left by jets in the atmosphere are only ice particles and contain no harmful chemicals. "Contrails are line-shaped clouds or 'Condensation trails' composed of ice particles that are visible behind jet aircraft engines under certain atmospheric conditions and at times can persist", says the notice, posted to the EPA’s website Friday. "EPA is not aware of any deliberate actions to release chemical or biological agents into the atmosphere". Theorists have posited that the chemicals are meant to control the climate, to harm humans or to kill them. The fact sheet from the EPA and other federal agencies like the Federal Aviation Administration and the National Oceanic and Atmospheric Administration was first published in 2000, when the chemtrails conspiracy became popular on the Web. An EPA spokeswoman said the agency frequently receives questions about chemtrails.
  10. Smith, Oliver (24 September 2013). "'Chemtrails' and other aviation conspiracy theories". The Telegraph. Retrieved 11 December 2016. So persistent is the chemtrail theory that US government agencies regularly receive calls from irate citizens demanding an explanation...The conspiracy theory took root in the Nineties, with the publication of a US Air Force research paper about weather modification...Governments and scientific institutions have of course dismissed the theories, and claim those vapour trails which persist for longer than usual, or disperse to cover a wide area, are just normal contrails.
  11. "chemtrail". Oxford English Dictionary (Third ed.). Oxford University Press. December 2011.(subscription required)
  12. Paul Simons (27 September 2013). "Weather Eye: contrail conspiracy". The Times. This conspiracy idea took hold in 1996 when the US Government was accused of trying to modify the weather for military means(subscription required)
  13. Reynolds, Jay (1 March 1999). "Those Mysterious Lines in the Sky". Veritas. Archived from the original on 17 August 2000., cited in USAF Contrails page.
  14. "Aircraft Contrails Factsheet" (PDF). United States Environmental Protection Agency. September 2000.
  15. Knickerbocker, Brad (14 March 2015). "EPA debunks 'chemtrails,' further fueling conspiracy theories (+video)". Christian Science Monitor.
  16. Cama, Timothy (13 March 2015). "EPA confronts 'chemtrails' conspiracy talk". TheHill.
  17. "The "Chemtrail" Hoax". Air Force. Archived from the original on 2 December 2002. Retrieved 7 May 2010.
  18. "Weather as a Force Multiplier: Owning the Weather in 2025". Fas.org. 1996. Archived from the original on 16 July 2009.
  19. "Aircraft Contrails Factsheet" (PDF). United States Environmental Protection Agency. Retrieved 30 August 2008.
  20. Poladian, Charles (22 July 2013). "CIA Exploring Geoengineering, Ways To Control Weather, To Reverse Globing Warming: Report". International Business Times.
  21. Thomas, William (Summer 2002). "Stolen Skies: The Chemtrail Mystery". Earth Island Journal. Retrieved 30 August 2008.
  22. Hamilton, Dan (7 April 2009). "Contrails vs. Chemtrails". Fox12 news at nine. Fox12 Idaho KTRV-TV. Archived from the original on 12 April 2009. Retrieved 11 April 2009.
  23. Ferrell, Jeff (21 December 2007). "Chemtrails: Is U.S. Gov't. Secretly Testing Americans 'Again'?". Shreveport, LA. Archived from the original on 31 August 2011. Retrieved 28 July 2009.
  24. Haenggi, Michael (2003). Boeing Widebodies. Zenith Press. p. 15. ISBN 978-1610607070.
  25. Kaur, Harmeet (23 October 2019). "Edward Snowden searched the CIA's networks for proof that aliens exist. Here's what he found". CNN. Retrieved 23 October 2020.
  26. starting minute 30:40 on https://www.youtube.com/watch?v=efs3QRr8LWw
  27. Benjamin Radford for Discovery. 1 May 2014. Viral Video Claims to Prove 'Chemtrails' Conspiracy
  28. "The Man Who Tricked Chemtrails Conspiracy Theorists". Vice. 13 October 2014. Retrieved 6 February 2017.
  29. "Chris Bovey – What are they spraying?" – via Facebook.
  30. Cairns, Rose (March 2016). "Climates of suspicion: 'chemtrail' conspiracy narratives and the international politics of geoengineering" (PDF). The Geographical Journal. 182 (1): 70–84. doi:10.1111/geoj.12116. Preprint available here
  31. Fountain, Henry (15 August 2016). "Scientists Just Say No to 'Chemtrails' Conspiracy Theory". The New York Times. Retrieved 26 August 2016.
  32. "Chemtrails Conspiracy Theory". David Keith Lab, Harvard. Retrieved 16 December 2016.
  33. Poladian, Charles (22 July 2013). "CIA Exploring Geoengineering, Ways To Control Weather, To Reverse Globing Warming: Report". International Business Times. Retrieved 15 March 2014.
  34. Hodapp, Christopher; von Kannon, Alice (2008). "Conspiracy Theories & Secret Societies for Dummies". Archived from the original on 13 July 2011. Retrieved 10 November 2010.
  35. Mercer, A. M.; Keith, D. W. & Sharp, J. D. (2011). "Public understanding of solar radiation management". Environmental Research Letters. 6 (4): 044006. Bibcode:2011ERL.....6d4006M. doi:10.1088/1748-9326/6/4/044006.
  36. Tingley, Dustin; Wagner, Gernot (31 October 2017). "Solar geoengineering and the chemtrails conspiracy on social media". Palgrave Communications. 7. doi:10.1057/s41599-017-0014-3.
  37. "Space Preservation Act of 2001 (2001 – H.R. 2977)".
  38. "Many Kucinich backers are out there – way out". Cleveland.com. 13 March 2001. Archived from the original on 4 November 2007. Retrieved 26 November 2010.
  39. Bethel, Brian (1 July 2008). "Abilene man wants to warn you about the dangers of 'chemtrails'". Abilene Reporter-News. Archived from the original on 26 March 2014. Retrieved 20 October 2008.
  40. "A Petition to the Canadian House of Commons: The Government's Response". Response. Holmestead.ca. Retrieved 13 April 2009.
  41. "37th Parliament, 2nd Sessions Edited Hansard; Number 110 Contents". Publications: Debates: Committees of the House: Petitions: The Environment 1030. Parliament of Canada. 3 June 2003. Retrieved 13 April 2009. Mr. John Herron (Fundy–Royal, PC): Mr. Speaker, I am presenting a petition on behalf of Mr. Brian Holmes of Ontario regarding aerial spraying. Mr. Holmes has collected signatures from across the country from concerned Canadians who believe that chemicals used in aerial sprayings are adversely affecting the health of Canadians. The petitioners call upon Parliament to stop this type of high altitude spraying. The petition has been duly certified by the clerk and I present it at this time.
  42. "Points to Ponder: Access to Information Act". Chemtrails – spraying in our sky. Holmestead.ca/. Retrieved 13 April 2009.
  43. "A Petition to the Canadian House of Commons". Chemtrails – spraying in our sky. Holmestead.ca/. Retrieved 13 April 2009.
  44. "Elliot Morley, former MP, Scunthorpe". TheyWorkForYou. Retrieved 16 April 2017.
  45. "House of Commons Hansard – 8 November 2005: Column 314W–315W". United Kingdom Parliament. 8 November 2005. Retrieved 12 March 2009. Mr. Morley: The Department is not researching into chemtrails from aircraft as they are not scientifically recognised phenomena.
  46. Fleming JR (2010). Fixing the Sky: The Checkered History of Weather and Climate Control. Columbia Studies in International and Global History. Columbia University Press. p. 103. ISBN 9780231144131.
  47. Bowerman, Mary (16 August 2016). "Scientists disprove airplane 'chemtrail' theory". USA Today.
  48. Kuhn, P. M. (September 1970). "Airborne Observations of Contrail Effects on the Thermal Radiation Budget". Journal of the Atmospheric Sciences. 27 (6): 937–942. Bibcode:1970JAtS...27..937K. doi:10.1175/1520-0469(1970)027<0937:AOOCEO>2.0.CO;2.
  49. R.G. Knollenberg (October 1972). "Measurements of the Growth of the Ice Budget in a Persisting Contrail" (PDF). Journal of the Atmospheric Sciences. 29 (7): 1367–1374. Bibcode:1972JAtS...29.1367K. doi:10.1175/1520-0469(1972)029<1367:MOTGOT>2.0.CO;2.
  50. Laakso, A.; Partanen, A. I.; Kokkola, H.; Laaksonen, A.; Lehtinen, K. E. J.; Korhonen, H. (2012). "Stratospheric passenger flights are likely an inefficient geoengineering strategy". Environmental Research Letters. 7 (3): 034021. Bibcode:2012ERL.....7c4021L. doi:10.1088/1748-9326/7/3/034021.
  51. Berman, Bob (2009). "Applying Occam's razor: problem solving isn't always a clean shave". Astronomy. 37 (9): 14. Archived from the original on 13 April 2014. (subscription required)
  52. Shearer, Christine; West, Mick; Caldeira, Ken; Davis, Steven J. (1 January 2016). "Quantifying expert consensus against the existence of a secret, large-scale atmospheric spraying program". Environ. Res. Lett. 11 (8): 084011. Bibcode:2016ERL....11h4011S. doi:10.1088/1748-9326/11/8/084011.
  53. Fritz, Angela (16 August 2016). "Scientists tell the world: 'Chemtrails' are not real". The Washington Post.

Further reading
Abstract: "Bureau of Reclamation cooperated with California Department of Water Resources to design and implement a snowpack augmentation program to increase runoff to Oroville Reservoir. The program involves the collection of data to document physical processes leading to increased precipitation. This report summarizes the main results from 3 yr of in-situ physical studies and statistical analysis of precipitation data collected during 87 randomized seeding cases. Liquid propane released from high elevation sites has proven to be a viable, reliable method of seeding wintertime clouds in the Sierra Nevada."

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