Recently I stumbled into a conversation about contrails (or chemtrails depending on your point of view). I believe some conspiracy theories are true, but we must look at each one separately and assess the plausibility of the claims and the quality of the arguments.
I dislike a lot of things about governments – especially after the past 3 years. I believe that governments (and their accomplices) are capable of doing unbelievably stupid and reckless things. Do I think it is possible that some governments are secretly spraying chemicals or doing climate control experiments? Yes – it is possible. But to make a stronger claim than that we need good quality evidence and good quality arguments.
Firstly, let’s look at the phenomenon involved here. It is white lines in the sky – like those shown in the picture below (source: metoffice.gov.uk).
The conventional explanation for these lines is that they are condensation trails (contrails) from aircraft engines.
Contrails
Water is a by-product of aircraft engine exhaust and under suitable atmospheric conditions (eg. pressure, temperature, humidity), the water vapor left behind as the aircraft speeds along will condense and form what is essentially a cloud. Over time contrails smear, disperse, or simply evaporate [1] (see note 2).
There’s an obvious potential for bias here. When an aircraft is at 35,000 ft it is very difficult to see – and you cannot hear it. Most of the time we won’t be aware of aircraft passing by high overhead or nearby. But when the conditions are right for contrails, then you will start noticing them. A contrail can last for many hours, so it won’t take many aircraft passing by at high altitude to create white lines crisscrossing the sky.
Some people have said there seem to be more of these trails now than there used to be. There are a few possible innocent explanations for that, one of which is that there are more aircraft in operation now than there used to be. But it isn’t a new phenomenon – there are pictures of aircraft contrails going back many decades. I can remember seeing them as a boy.
Chemtrails
So, what is the chemtrails theory? The idea is that those white lines are trails of chemicals being sprayed to control the weather, climate change mitigation, or some sinister purpose. I wouldn’t be surprised if there has been a resurgence of interest in chemtrails during Covid because people didn’t expect to see aircraft during lockdowns (or maybe had more time to look at the sky), and frankly our governments have recently given us good reason to trust them even less.
My explanation of contrails doesn’t rule out the chemtrails theory. Probably most chemtrails believers would agree that the lines are caused by aircraft. The real question is – what is in the lines? Is it simply water condensation and a few other aircraft engine by-products? Or is it something governments aren’t telling us about?
I can remember a few years back there was a large-scale aerial spraying program carried out in parts of Auckland to eliminate a moth which was considered a threat to agriculture [2]. I remember that Aucklanders weren’t happy about it at the time. There have been some infamous cases of aerial spraying elsewhere such as that of Agent Orange used during the Vietnam war [3].
Cloud seeding (with silver iodide or some other chemical) to make it rain has been around for years. Apparently, it hasn’t produced compelling results [4].
More worryingly, under the heading “geoengineering” are climate change related proposals, such as injecting certain chemicals into the stratosphere to reflect away sunlight [5].
There is no question that spraying substances from planes is possible, and that it has been done in the past. Should we be worried that governments might be up to something now? They seem to have forgotten that they serve the people who elected them, and that they have a duty to be truthful, transparent and accountable. Climate change hysteria has clearly returned after taking a temporary backseat to Covid hysteria, so the potential for stupid and reckless policies is real. As with Covid, they are so obsessed with climate change that they will not listen to dissenting views.
For these reasons we should be alert – but it doesn’t mean that the white lines people are seeing in the sky are government geoengineering projects.
Inference to the best explanation
We have good reasons to be concerned about what our governments are up to. But we should also try to be rational because that will make it more difficult for our concerns to be dismissed.
There is a principle in science called inference to the best explanation. As the name suggests it just involves deciding which of the possible explanations best fits the observations or evidence. But it’s also important to be prepared to change your preference if the evidence changes.
The main evidence that we have here is the observation of white lines in the sky. These observations fit well with both the ordinary aircraft contrails explanation and the secret government project explanation. If you are skeptical of the chemtrails theory you might be surprised at me saying that – but remember that if it was true that the government was spraying chemicals into the atmosphere then it might look similar to ordinary aircraft contrails (see note 1).
So if both explanations seem to fit quite well with the observations, how do we decide which is best?
Even if we only have this much evidence, there are some principles which can help us choose one option over the other. There is a principle called Occam’s Razor which says that all else being equal then we should choose the simpler explanation. A similar principle attributed to astronomer Carl Sagan is that extraordinary claims require extraordinary evidence.
Of the two explanations we are currently considering, I think you’d have to agree that ordinary aircraft contrails is the simpler and less extraordinary one. So that is the one we should prefer (pending further evidence that might change our minds).
But there may be things we can do to gather more evidence. For example, we may be able to see the aircraft travelling along at the head of the contrail so we may be able to satisfy ourselves that it’s just a commercial jet passing over. Or we can try matching up the lines with an aircraft tracker app. Or maybe check if it might be military aircraft doing training flights. We could also try to find specific evidence supporting the geoengineering explanation.
Contrails from ordinary commercial aircraft operations or secret government geoengineering project? People are suspicious of governments. But that fact alone is not evidence.
Note 1. I have oversimplified things here for the sake of the article. There are other factors we could consider such as which option best explains the large number of lines. Also, it isn’t really an either/or question – it could be true that most lines are contrails but there are also secret government experiments going on.
Note 2 (added 5th May). To be clear, I am not making the claim that aircraft exhaust contains only water. We should certainly be concerned about whether aircraft exhausts are polluting/harmful, but that is a different topic to the one I am discussing in this article.
References:
[1] https://en.wikipedia.org/wiki/Contrail
[2] Plant pesticides in New Zealand. https://en.wikipedia.org/wiki/Pesticides_in_New_Zealand
[3] Agent Orange in Vietname war. https://en.wikipedia.org/wiki/Agent_Orange#Use_in_the_Vietnam_War
[4] Cloud seeding. https://en.wikipedia.org/wiki/Cloud_seeding
darryl.betts 
Great post. There is actual evidence though that chemtrails are a real thing, and I’d be careful of citing Wikipedia. That being said, you made some very valid points.
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