The trail of clouds that billow from an airplane streaking across the sky can be mesmerizing for children and adults alike. Jet engine traffic has become so common that it's not unusual to see several lingering streaks in the afternoon. And though many consider the streaks beautiful against a bright blue sky, others are alarmed about them. Concerns range from the idea that these streaks could exacerbate global warming to more elaborate theories that the government has secretly been dumping harmful substances on the land.
Before we get into the various theories about the possible harmful effects, let's discuss the scientific explanation for these streaks. Jet engines spew out very hot air. And, because water vapor is one of the byproducts of the exhaust, the air is also very humid. However, high in the atmosphere where these jets fly, the air is typically very cold -- often lower than -40 degrees Fahrenheit. Additionally, the atmosphere up there is often of low vapor pressure, or the force exerted by a gas on the surrounding environment.
When a jet engine is spewing out hot, humid air into an atmosphere that is cold and has low vapor pressure, the result is condensation. The water vapor coming out of the engine quickly condenses into water droplets and then crystallizes into ice. The ice crystals are the clouds that form behind the engine. This is why the streaks are called contrails, short for "condensation trails." To help explain it, scientists liken it to seeing your breath on cold days. You may have noticed that puffs of breath dissipate quickly on dryer days. The same is true of contrails: When the atmosphere is more humid, the contrails linger, but when the atmosphere is dry, the contrails disappear more quickly.
This explanation makes sense. But, as author and airline pilot Patrick Smith tells readers, the contrails consist of not just ice crystals and water vapor but also other byproducts of engine exhaust. These include carbon dioxide, nitrogen oxides, sulfate particles and soot [source: Smith]. Some point out that these, in addition to the extra cloud cover, can have negative environmental effects. And conspiracy theorists have nicknamed contrails "chemtrails" under the suspicion that the government is taking advantage of this scientific phenomenon to secretly release other substances into the atmosphere.
The Chemtrail Conspiracy Theories
A U.S. Environmental Protection Agency fact sheet on contrails explains that contrails, even long-lasting ones, are simply trails of condensation and are not harmful. However, conspiracy theorists have become suspicious that the contrails expelled from jets today are thicker and linger longer than they did in the past. So, while they accept that contrails are a natural byproduct of jet engines, their suspicion is that the government has since used that excuse to put other substances in them, creating chemtrails. In addition, conspiracy theorists latch on to anecdotal evidence that connect epidemics of flulike symptoms to instances of contrails. Those who believe that there's something fishy about contrails have come up with several theories to explain what the government could be covering up.
One of the more extreme theories says that the government is intentionally spraying people with harmful substances in order to experiment with the effects -- or even to "weed out" the sick and elderly. However, many reputable scientists dismiss these theories on the grounds that such experiments would be of no real use. The "chemtrails" would be released so high in the atmosphere that unpredictable winds would move them around significantly, making such experiments worthless and unreliable [source: Hodapp]. Others speculate that the government is dumping barium salt aerosol on the land in order to assist in radar mapping for defense purposes [source: Knight].
Still others believe that the government could be experimenting with weather manipulation for defense purposes. This actually isn't as much of a stretch as it may seem. As long ago as the 1950s, the British were able to successfully "seed" clouds with salt, dry ice and silver iodide to make rain (see the sidebar on this page). It would seem that weather manipulation, then, is a very possible and effective military defense tactic. Conspiracy theorists believe it might have connections to HAARP, the High Frequency Active Auroral Research Program, which studies the atmosphere to advance communication and navigation systems.
Another popular theory is that chemtrails are well-intentioned attempts by the government to combat global warming or the depletion of the ozone layer by spraying particles to reflect the sun's radiation. However, if this is true, it's ironic that (non-conspiracy theorist) environmentalists blame contrails for polluting the skies. They say that jet traffic has become so bad that the sheer cloud cover from contrails, which can be seen from space, has been negatively affecting the environment, possibly contributing to global warming.
So, whether you consider the conspiracy hype healthy skepticism or paranoia, contrails (along with the fuel consumption and energy use of the air traffic industry that cause them) are certainly an area of concern for the environment.
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- Hodapp, Christopher, Alice Von Kannon. "Conspiracy Theories & Secret Societies For Dummies." For Dummies, 2008. (Feb. 28, 2011)http://books.google.com/books?id=xAvZkw9muqsC
- Knight, Peter. "Conspiracy Theories in American History: An Encyclopedia, Volume 1." ABC-CLIO, 2003. (Feb. 28, 2011)http://books.google.com/books?id=qMIDrggs8TsC
- NOAA. "What is a contrail and how does it form?" National Oceanic and Atmospheric Administration. (Feb. 28, 2011)http://www.wrh.noaa.gov/fgz/science/contrail.php?wfo=fgz
- Smith, Patrick. "Ask the Pilot: Everything You Need To Know About Air Travel." Penguin, 2004. (Feb. 28, 2011)http://books.google.com/books?id=xqqGGLFa4Z8C
- Tyson, Peter. "The Contrail Effect." Public Broadcasting Station. NOVA. April 2006. (Feb. 28, 2011)http://www.pbs.org/wgbh/nova/sun/contrail.html
- Vidal, John and Helen Weinstein. "RAF rainmakers 'caused 1952 flood.'" The Guardian. Aug. 30, 2001. (Feb. 28, 2011)http://www.guardian.co.uk/uk/2001/aug/30/sillyseason.physicalsciences