I wouldn't normally try to disprove this kind of conspiracy theory, but I'm seeing references to it more and more frequently, and more and more people who I encounter seem to be becoming drawn in to some kind of belief that the government is using commercial aircraft to spray the populace, not just in this country, but around the world (predictably, America seems to be rife with this conspiracy theory).
There seem to be two factors driving this theory; the first of which is the predictable mistrust and hatred of the government, and the second of which is the observation that some contrails (the condensation clouds left by aircraft at high altitudes) linger for much longer than others, and so the ones which linger are believed to be part of some government programme to spray the population with chemicals.
There are insurmountable problems with this conspiracy theory, and some of them are described below:
- The most obvious and gaping flaw with the theory from my perspective, is that it is the contrails which linger in the atmosphere which are picked out as chemtrails. This makes no sense, as surely a chemical dispersal system which lingers at high altitude is a poor method of delivering any chemical? If any, wouldn't the contrails which don't linger be more likely to be chemtrails?
- Further to the gaping flaw in scientific understanding above, the phenomenon of variance in contrail duration is well understood by scientists as the result of normal variance in atmospheric conditions. Humid air inhibits evaporation, and so the more humid the atmosphere is, the longer the contrails are likely to last. As with many conspiracy theories, this theory completely ignores and sidesteps fundamental and well established scientific understanding.
- The number of people involved in this kind of conspiracy would be vast. Even just considering the people of, say, the USA, you would have government officials, bureaucrats, chemical companies, their workers, logistics technicians, the airline executives, pilots, flight engineers, aircraft ground crew, airport staff, and probably many others, who all know at least something about what's going on here, and are silent. There has been no compelling evidence presented by anyone in any related field to support the allegations of chemical spraying. Given that the US in particular has an abysmal record of being able to cover up anything for very long, it seems very implausible that they would be able to cover up something like this, which would involve many more civilians than other conspiracy theories. When you consider that this is a global conspiracy, supposedly spanning many governments, it becomes even more implausible that they haven't been caught out red handed yet.