Boeing 787 emits incredible contrail - what causes them, and are 'chemtrails' part of a global conspiracy?

The truth

Governments and scientific institutions have, of course, dismissed the theories, and insist those vapour trails which persist for longer than usual, or disperse to cover a wide area, are just normal contrails. The variety of contrails seen in the sky is due to atmospheric conditions and altitude, they say, while grid-like contrails are merely a result of the large number of planes that travel along the same well-worn flight lanes.

"The combination of high relative humidity and a nice sunrise gave this contrail a nice deep colour as the contrail created its own shadow," explainer Lou Boyer, who captured the video above.

Patrick Smith, a US pilot, dismisses the conspiracy theory in his book about air travel, Cockpit Confidential. "Contrails are formed when humid jet exhaust condenses into ice crystals in the cold, dry, upper-level air –­ it's not unlike the fog that results when you exhale on a cold day," he says. "Contrails are clouds, you could say. Water vapour, strange as it might sound, is a byproduct of the combustion within jet engines, which is where the humidity comes from. Whether a contrail forms is contingent on altitude and the ambient atmospheric makeup – mainly temperature and something known as vapour pressure.

"I refuse to devote valuable page space to the so-called 'chemtrail' conspiracy theory. If you know what I'm talking about and wish to argue the matter, feel free to email. If you don't know what I'm talking about, don't worry about it."

In 2000, the Federal Aviation Administration, the US national aviation authority, teamed up with the Environmental Protection Agency (EPA), the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA), to create a detailed report aimed at dispelling the rumours once and for all. It clearly didn't work. The EPA reissued the document as recently as 2015.

The report reads: "Aircraft engines emit water vapour, carbon dioxide, small amounts of nitrogen oxides, hydrocarbons, carbon monoxide, sulfur gases, and soot and metal particles, formed by the high-temperature combustion of jet fuel, during flight. Of these emittants, only water vapour is necessary for contrail formation.

"If the humidity is high (greater than that needed for ice condensation to occur), the contrail will be persistent. Newly formed ice particles will continue to grow in size by taking water from the surrounding atmosphere. The resulting line-shaped contrail extends for large distances behind an aircraft. Persistent contrails can last for hours while growing to several kilometres in width and 200 to 400 meters in height. Contrails spread because of air turbulence created by the passage of aircraft, differences in wind speed along the flight track, and possibly through effects of solar heating." Now you know.

It concluded that "persistent contrails pose no direct threat to public health" but added: "Contrail cloudiness might contribute to human-induced climate change."

So, while "chemtrails" are widely considered a myth, contrails themselves may actually be harming us by contributing to global warming.

There are a couple of other interesting facts about contrails.

Military aircraft will sometimes fly at a particular altitude to avoid producing them, and therefore evade detection.

Also, when a plane is travelling towards an observer on the ground, it may emit a contrail that appears to be vertical. In November 2010, The Pentagon was left baffled by what was reported to be a "mystery missile launch" off the coast of California, but eventually concluded that it was an probably an aircraft contrail.

Six other air travel conspiracy theories

1. Oxygen masks are there to keep you docile

Brad Pitt is to blame for this one. In the film Fight Club, his character Tyler Durden says the following:

"You know why they put oxygen masks on planes? Oxygen gets you high. In a catastrophic emergency, you're taking giant panicked breaths. Suddenly you become euphoric, docile. You accept your fate. It's all right here [points at an emergency instruction manual on a plane]. Emergency water landing – 600 miles an hour. Blank faces, calm as Hindu cows."

This, of course, is nonsense. Those oxygen masks could well save your life – and they definitely don't get you high.

See also: Why there are oxygen masks on planes

2. Denver Airport is hiding a secret military base

Denver International Airport has found itself under intense scrutiny from conspiracy theorists since it opened in 1995. Philip Schneider, a structural engineer turned whistle-blower who died in mysterious circumstances in 1996, claimed that beneath the airport lies a vast underground facility, prompting suggestions that the airport is actually hiding a secret military base or even a concentration camp. And why, ask conspiracy theorists, do the runways form the shape of a swastika?

Even the artwork on display fell under the spotlight. Bizarre murals showing somewhat disturbing and apocalyptic scenes inside the main terminal were said to depict the true agenda of the "New World Order". Apparently.

For more on the odd claims, plus Denver Airport's response, follow this link.

3. The brace position will break your neck

Numerous theories have been proposed about the purpose of the position passengers are told to adopt before an impact. Some have suggested that it is only useful for preserving passengers' teeth, allowing for easier identification (using dental records) after a crash. Another is that the position actually increases the chance of a quick death, by breaking your neck, and is subsequently recommended by airlines to reduce their own insurance bill.

While ongoing compensation payments to a seriously injured passenger may cost more than a single payment to the relatives of a deceased one, such theories have been widely debunked by research.

See also: Does the brace position save lives?

4. Planes disappear in the Bermuda Triangle

The roughly triangular area bounded by Miami, Bermuda and Puerto Rico is where dozens of aircraft and ships are said to have vanished in unusual circumstances, with the disappearances attributed to paranormal or extraterrestrial activity.

Notable incidents include the disappearance of Flight 19, a US Navy bomber, on December 5, 1945, as well as the aircraft sent to search for it; that of a Douglas DC-3 aircraft with 32 people on board in 1948; and a mid-air collision between two US Air Force planes in 1963.

See also: A trip to paradise in the North Atlantic

5. The Wright brothers weren't the first to fly

Some believe the Wright brothers did not in fact build the world's first successful aeroplane. German-born Gustav Whitehead should get the credit, they say, as evidence suggests he took to the sky two years earlier. They add that US institutions will not accept Whitehead's role in the birth of aviation because of their indebtedness to the Wrights' legacy – a 1948 contract between the estate of Orville Wright and the Smithsonian museum means it is legally obliged to call the Wright brothers the first to fly.

6. Amelia Earhart faked her own death

The pioneering aviator Amelia Earhart vanished over the Pacific Ocean in 1937 while attempting to circumnavigate the globe. Various reasons have been given for her disappearance. Some claim she was a spy, and that she was shot down and captured by Japanese forces; some believe she faked her own death; and a few even claim she was abducted by aliens. Earlier this year researchers claimed they had discovered remnants of her aircraft using sonar readings.

The Telegraph, London

See also: Why planes fly at 35,000 feet

See also: Six incredible planes you'll never get to fly on