Contrails v Chemtrails: The Science That Debunks The Conspiracy

Contrail over Kildare. Image Author

Contrail over Kildare. Image: Author

There are those who claim that the trails we see behind aircraft high in the sky are not the normal condensation of water vapour from the hot exhaust gases but are in fact chemicals that are being deliberately sprayed upon us by government agencies for some dark and sinister reasons. When asked to prove their claims, however, their response is invariably either just a video or blog of someone else making the same unsubstantiated claim, or a simple “Well why don’t you prove that they’re NOT chemtrails!”. Proof has been given time and time again but ok, here it is one more time, using only sound scientific methods and no political mumbo-jumbo.

Actually, it should not be for me or any reasonably-minded person to reprove something that has always been a normal and scientifically-accepted fact of life. If others come along and claim that it is something totally new and different then it is actually up to them to provide evidence that proves beyond doubt that the original theory is wrong. The simple fact is that this evidence does not exist, but this does still not deter them from making these claims and denouncing anyone who tries to argue against them.

I am not denying that geo-engineering, still just a theoretical exercise, could be easy enough to try out, given the right modifications to an appropriate aircraft, or that cloud-seeding experiments have been carried out (but these only consist of silver iodide crystals from burning flares and not actual dumping of material). I am actually totally against the whole idea of trying to geo-engineer our way out of what is really not a problem, in my opinion. In any case, it would be such an inefficient method of poisoning us, as the resulting concentration of chemicals in the air would be the equivalent of only half a teaspoon in 4 billion Olympic-size swimming pools! (See my calculations at the end of this article).

What I AM denying is the claim that the trails we see from normal commercial airliners, both with our own eyes and in the photos of our readers, are chemtrails, as is claimed by a certain number of conspirators every time a reader shares a photo with us. Using such sites as it is so easy to check at any minute of the day what planes are flying overhead, generating the contrails we are seeing. To claim that these planes are not just innocent airliners but are being used for dumping harmful chemicals requires specific proof.

Has anyone ever seen a refueling truck loading anything other than fuel into the tanks as you board a plane? Have you ever spotted nozzles on the wings spraying these chemicals as you look out the window as you fly along? Do you think the airlines are in on this and agree to carry the extra weight of these substances? No, I didn’t think so.

Anyway, what are contrails (CONdensation-TRAILS)? They are plumes of ice-crystals formed by the condensation and freezing of water vapour in the exhaust-gases of an aircraft flying at high altitudes and under the right conditions. As fuel (petrol, diesel, avgas, Jet-A1, kerosene, natural gas, etc.) is a hydrocarbon, burning it produces carbon dioxide (CO2) and water vapour (H2O), along with other materials, such as nitrogen oxides, sulphates, hydrocarbons, soot, metal particles, etc. This applies to planes as it does to trains, cars, trucks, buses, motorbikes, lawnmowers, boilers, etc. Different fuels contain different additives and produce different levels of these by-products, but they all produce CO2 and water vapour. That is basic Junior Cert chemistry and something that cannot be denied. The difference with planes is that they operate in conditions very different to these other vehicles.

I am now going to take the main arguments that the conspirators use in their claims that the clouds we see can not be simple contrails, and will give a scientific explanation of why they are wrong and what is actually happening. In each case I will first give some simple analogies to illustrate the reason, then give a deeper scientific explanation. That way no one can claim it’s above their comprehension.

But first, some definitions:

Dewpoint: The temperature at which condensation (fog/cloud) will occur if air is cooled enough. Humid air has a higher dewpoint than dry air. The relative humidity is 100% when the dewpoint and temperature are equal.

Relative humidity: The amount of water vapour in the air, expressed as a percentage of the total amount of water vapour the air can hold at that temperature and pressure. Warm air can hold a lot more vapour than cold air. 100% means the air is totally saturated and condensation (fog/cloud) will form.

Conspiracy Claim 1.“Contrails only last for seconds but these ones lasted for hours, therefore they must be chemtrails”.

ACTUAL REASON: Contrails can last from seconds to hours, depending on the relative humidity at cruising altitudes. If it is above around 70% then the contrails can last for hours.

ANALOGIES: In summer you don’t normally see your breath, in cold winter you normally do. In summer you don’t see truck exhausts form water vapour clouds, in winter you
normally do, and they can last for relatively long times (especially in places like Siberia). If you throw a saucepan of boiling water in the air in summer it will
simply fall to the ground as water, with some of it evaporating on the way. If you do the same in winter (below around -20 °C) then it will freeze instantly into a cloud of fine ice particles and hang around a for much longer. This video illustrates this perfectly. Seen from below we see the larger ice-particles falling quickly to the ground but the main cloud of tiny crystals remains suspended and drifts slowly, just like a contrail.

THE SCIENCE: Many days we don’t actually see any trails at all from aircraft flying high above us as the trails dissipate as soon as they are formed. The air at cruising altitudes is very cold (-40 to -60 °C) and usually very dry (low relative humidity). The water vapour from the exhaust gases alone is not enough to form a contrail. Knollenburg (1972) gives a breakdown of typical components of aircraft exhaust gases, with around 1.37 kg of water vapour released per kg of fuel burned. The study found that exhaust gases contained around 1.7 g of water vapour for every metre flown, but found actual persistent contrails to contain at least 30,000 times that level (20,700-41,200 g per metre). This means that the overwhelming majority of the water in contrails comes from the atmosphere, with only around 1 in every 30,000 molecules originating from the burning of the fuel. It is therefore clear that relative humidity at cruising altitude needs to be relatively high for contrails to form and be visible, and very high (above around 70%) for them to persist for long periods.

We get these conditions from time to time and place to place, especially a few hundred miles ahead of an approaching depression (warm front), and to the west of an upper ridge-axis, among others. We normally see natural cirrus clouds (thin, high, wispy clouds) in these conditions, but even when conditions are not quite humid enough for natural cirrus to form on their own they can be right for contrails, as the exhaust particles (soot, etc.) act as cloud condensation nuclei (CCN) around which water vapour can condense and freeze into ice-crystals. This is why we can sometimes see contrails without natural cirrus, but normally we would see some cirrus too, even if just a few random wisps. If the relative humidity is below around 60% then the ice-crystals can sublimate (turn from solid directly to gas) fairly quickly and dissipate but if it’s above around 70% this sublimation process is much slower and the contrail can last for hours. Contrail ice-crystals are also much smaller (0.001 – 0.1 mm) than cirrus crystals (0.01 – several mm), which allows them to remain suspended for longer.

Conspiracy Claim 2. “I saw two aircraft flying in the same area. One aircraft’s contrail dissipated within a few seconds, the other’s grew and lasted for hours. The second aircraft was obviously spraying chemicals”.

ACTUAL REASON: They were simply flying at different altitudes and/or were different types of aircraft (engine).

ANALOGIES: Your bathroom mirror doesn’t fog up when you first take a shower. It only does so after a while, when there is enough vapour in the room to increase the dewpoint to the temperature of the mirror, allowing the vapour to condense onto.

A small cup of coffee makes a smaller steam cloud than a large open pot of coffee. The pot has a larger volume of steam rising and condensing off it, which rises to a greater height before evaporating, just as a larger engine produces more emissions than a smaller one.

THE SCIENCE: Cirrus clouds are very high up but relatively thin (sometimes only a few hundred metres deep), therefore there is only a narrow layer in which conditions are right for their formation. The same goes for contrails. Two identical aircraft flying at different altitudes can therefore produce very different contrails as the temperature and humidity can be very different.

Look at this sounding (plot of temperature, dewpoint and wind measurements from an instrument attached to a weather balloon) for Camborne, in the extreme southwestern
tip of England, around the middle of the day on August 22nd, 2013.


Airliners cruise at between around 30,000-40,000 ft (9,000-12,000 m). The sounding shows cold and mainly dry upper levels (the temperature and dewpoint curves are far apart), however there is a very thin humid layer just below 300 hPa (9,500 metres), where the dewpoint curve (left) shoots over to almost meet the temperature curve (right), meaning high relative humidity. We would expect very few contrails in this scenario as only those planes flying exactly within that humid layer will produce contrails. Other layers are just too dry. The actual data points from this sounding show that humid layer to be at around 9,116 metres (around 30,000 ft), with a relative humidity of 78%. Sure enough this high-resolution MODIS satellite picture for 11:40 UTC (around 20 minutes before the sounding) shows just one fresh contrail just south of Lands End, which shows as United Airlines flight 43, a Boeing 767-400 flying at 30,000 ft. It shows dozens of other aircraft at different heights all over southern England and the English Channel, but not one of these is producing a contrail as the levels they’re flying at are too dry. Not surprisingly they’re not producing chemtrails either!

Sometimes we see broken or very short contrails, i.e. with breaks, as in my photo at the top of this article. This can be caused by an aircraft climbing through a humid layer, or by the effects of gravity waves at altitude. The plane enters and exits humid areas as it flies along, giving a broken contrail. We also see this type of effect with natural transverse cirrus bands along which form perpendicular to the jetstream flow (strong winds at altitude). An aircraft flying parallel to the jetstream will be passing in and out of the humid areas that are causing the transverse cirrus, so its contrail will be discontinuous.

tranverse cirrus

Transverse cirrus bands form perpendicular to the jetstream wind, shown by the wide swathe of fibrous cirrus.

Two different types of aircraft flying at the same altitude can still produce different contrails. Different engines produce different-sized exhaust plumes, and newer engines produce cooler exhaust-gas temperatures than older engines. Cooler exhaust temperatures allow the contrail to form quicker, before the gases have a chance to mix with the ambient air, as the gas needs less time to cool to condense the vapour into ice-crystals. Engine contrails can also be affected by the aerodynamics of the aircraft wings, etc., and even the weight of the aircraft, which can strengthen wake-vortices and enhance contrails. In fact, some contrails are not even related to the engine exhaust gases at all and are merely condensation formed within the wake-vortices, where the pressure is locally lower than the surroundings. We can see that when landing or taking off on a very humid day.

To an observer on the ground it can be very difficult to accurately estimate the relative heights of two aircraft flying near eachother. They may SEEM to be at the same altitude but in reality they could be a few thousand feet apart and therefore in possibly very different ambient conditions.


These planes look they’re colliding but they’re actually at least 1,000 ft apart vertically.

Conspiracy Claim 3. “Those trails are in regular criss-cross patterns, so there is obviously some systematic spraying going on”.

ACTUAL REASON: Planes fly many different routes (called airways), which can cross eachother at points called Intersections.

ANALOGY: No need for one here, it’s pretty straightforward!

THE SCIENCE: Ireland’s airspace is very busy with transatlantic traffic, with hundreds of morning eastbound and afternoon and evening westbound flights every day. Ireland has actually done away with the upper airway system within its airspace, instead allowing aircraft to fly their own direct routes between intersections along the eastern and western borders of the airspace. This saves the airlines time and fuel, but also means no real set published flight paths, as there used to be previously. Planes cross paths all the time, depending on what the intersections they are flying between. Just off the east coast these flights all converge at a few intersections, which can give a more regular contrail pattern to an observer on the ground. The link above also shows the complexity of the airway system over the UK airspace and this video shows how busy traffic gets throughout different times of the day, especially the afternoon and evening in Europe.

Conspiracy Claim 4. “I never saw this many contrails when I was a kid so it must be chemtrails that I’m seeing now”.

ACTUAL REASON: There are more flights now than years ago. Engines are larger and produce cooler exhaust gases, which make it easier for contrails to form, as explained

ANALOGY: A room full of kids is a hell of a lot louder than a room with just one kid!

THE SCIENCE: Pretty much explained in the other points above. We should not, however, compare what we are seeing now to what we remember as kids. We all think that the
summers were better back when we were young, but there are no data to back this up. Our minds as kids were different to what they are now, having developed through all
the stages of cognitive development. In the same way, we were most likely not counting contrails back then and wouldn’t have probably noticed them much in any case.

Conspiracy Claim 5. “Children have lots of respiratory problems now and it’s due to chemtrails”.

ACTUAL REASON: This has to be the craziest claim I have heard from a conspirator. There are many more plausible and well-documented reasons for children’s health problems. The use of a sick child as proof of chemtrails is stooping to a new low.

THE SCIENCE: The science of the previous explanations debunks this claim as it proves that the chemtrails are not there in the first place. Increases in children’s health problems are well-documented and can be due to increased obesity, poor diet, less excercise, more time spent indoors, etc.


Satellite imagery is a perfect tool for spotting contrails. Visible imagery is good, but there are other types of imagery (IR, Water-vapour, RGB, Dust RGB, etc.) that show them up to varying degrees. These images are formed by filtering various wavelengths, which show up differences in cloud physics, such as small or large ice-crystals, thin or thick layers, etc.

The Eview image below of the Iberian peninsula at 1800 UTC this evening shows an area of persistent contrails over Biscay and the northern and northwestern parts of Spain and Portugal, with none showing up elsewhere. Comparing this image with the predicted 300 hPa relative humidity chart from the GFS model (underneath) shows that the contrails are forming right inside the area of >75% relative humidity, which stretches from the Pyrenees to central Portugal and up to Galicia. Other areas are too dry for contrails. This is a good example of how we can actually predict the areas that will have contrails.

Eview image of Iberia at 1800 UTC, 8 September 2013. Persistent contrails are visible over northern and northwestern Spain and Portugal. Image: Eumetsat

Eview image of Iberia at 1800 UTC, 8 September 2013. Persistent contrails are visible over Biscay and northern and northwestern Spain and Portugal. Image: Eumetsat

GFS 300 hPa relative humidity chart for 1800 UTC, 8 September, 2013. Image:

GFS 300 hPa relative humidity chart for 1800 UTC, 8 September, 2013. Image:


It only requires one test to prove a theory wrong, but in this article I have given several. Sometimes we see things that we cannot explain. Various theories circulate to try to explain them, and invariably some of these theories take on a political theme – a Them versus Us kind of thing. Some people are more prone to accepting these theories than others, and a quick check of the Facebook profiles of many of the conspirators on our page will confirm that.

This has been an effort to explain why their chemtrail theory is false on so many levels, and maybe some of them will finally see the light and accept that science rules over our imaginations 100% of the time.  I can, however, forecast even now the responses I will get to this article, as some people just want to believe in the alternative, for whatever reasons. I can do nothing about that. We are all different, but ignorance is no excuse for stupidity at any time.

Fergal – Irish Weather Online

UPDATE: Calculation of half a teaspoon in 4 billion Olympic-size swimming pools.

Just to highlight how unbelievably inefficient chemtrails would be as a method of poisoning people, I have done a quick calculation on how much chemicals would be added to the atmosphere every day if every single jet plane on the planet was spraying all of the time (turbprops use Jet A1 too, but for the benefit of the conspirators let’s assume they are all high-level jets). It is based on the daily consumption of Jet A1 fuel (which in 2010 was about 5,220,000 barrels/day) and assuming a very generous chemical contamination of 10% in the fuel. This level would, of course, be too high for the engines to operate, but hey, why let logic get in the way when it comes to the topic of chemtrails.

Overall, the resulting contamination of the atmosphere would be just 0.0000000000000000002844%, or the equivalent of just a half of a teaspoon of water in 4 billion Olympic-size swimming pools!

Here are my calculations. As most airliners normally cruise at between 33,000-39,000 ft, I have taken the average cruising altitude as 36,000 ft (11 km). They would therefore be contaminating a volume of the atmosphere (what I call the Cruisosphere) from that level down to the ground. By finding the total volume of this cruisosphere and the total amount of chemicals being sprayed into it we can find the resulting concentration in the air we breath.

Radius of Earth, R: 6370 km
Average cruise altitude, H: 36,000 ft (11 km)
Volume of a sphere: (4/3)Pi(R³)

Volume of Earth (radius 6370 km): 1,082,696,932,433 km³
Volume of Earth + Cruisosphere (radius 6370 + 11 km): 1,088,315,571,792 km³
Volume of Cruisosphere: 1,082,696,932,433 – 1,088,315,571,792 = 5,618,639,359 km³

The daily consumption of Jet A1 in 2010 was 5,219,510 barrels (1 barrel = 42 US gallons (162 litres), so that’s 843,994,767 litres, or 683,635,761 kg, given that the density is 0.81 kg/litre). Assuming a 10% chemical-contamination, this gives a total of 68,363,576 kg of chemicals sprayed through the fuel per day. This is, of course, making the huge assumption that they survive the combustion and come out of the exhausts unaffected – a highly unlikely scenario – but let’s carry on nevertheless. As we said, logic is not a word the conspirators have in their vocabulary.

This leads to a daily concentration of chemicals in the atmosphere of 68,363,576/5,618,639,359 = 0.01217 kg/km³ (i.e. 12.2 g (or one dessert-spoon) in a volume of 1 cubic kilometre).

The density of the atmosphere at sea level is 1.225 kg/m³ and at 11 km altitude it is 0.2978 kg/m³. This gives an average density throughout the Cruisosphere of: (1.225+0.2978)/2 kg/m³ = 0.7614 kg/m³ = 761,400,000 kg/km³. Multiplying this by the volume gives us the mass of the cruisosphere: 4,278,032,007,942,600,000 kg.

This lets us calculate the daily percentage chemical concentration: 100 x (0.01217/4,278,032,007,942,600,000) = 0.0000000000000000002844%

So only 2.8 of every ten billion billion grams of the atmosphere would be from chemicals. One Olympic-size swimming pool is 50 x 25 x 2 metres = 2,500 m³ (2,500,000 litres), so ten billion billion grams is four billion Olympic-size swimming pools. One teaspoon is 5 ml, so 2.8 g (ml) is just over half of that. This is all we have in our four billion swimming pools. Over a year it comes to just 1 litre.

NOW do you still think they’re spraying?

661 thoughts on “Contrails v Chemtrails: The Science That Debunks The Conspiracy

  1. And like a true sociopath he will lie about the context of his comment and deny his actual implication. He will continue to twist it until he looks innocent. There was nothing in the post he replied to that indicated I was telling you what to do, like a “mom”.

    • While at the same time avoiding those calculations I asked for.

      It’s one thing being an idiot behind an online username but it’s another when people know your full name and that you’re an artist from Dun Laoghaire. He’s not doing himself any favours there.

      • So we’re back to that again Fergal? We have been through this before, I have nothing to hide. Get my name out there and promote me if you like. Cool. Anyway what’s your point?
        You astound me man, when you call me an idiot behind a username haha.
        I sincerely mean it that I did NOT mean any reference to your Mother. Never in my lifetime have I disrespected anybody’s Mother. So apologies if you think I aimed that at you personally.
        It was a dig at Bill who appears to constantly dictate to you how to run you Blog.
        And now ye think I’m just being sweet to ye again…
        You guys. :D

      • I’ll show you the calculations on my way back from another photoshoot down your way. If you don’t believe me check out my trolling, artistic, idiotic, and can’t remember all the other names you and Bully have called me sofar on my fergalt youtube link. . Disgraceful Administration.
        How can your subscribers take you for real when you abuse them in a debate that you originally posted? Why did you even post it in the first place?
        I’ll txt you to let you know when and what time.
        Bet you’ll just happen to be “flying” that day.

      • You’re comments are there for all to see, Dec, so they can clearly make out the level of your contribution. You have never engaged in a scientific debate, you just posted some cryptic “fact” about pixels or something but resorted back to personal attacks when asked to show where you got it from.

      • Yes I know Fergal, of course my comments are there to see by all, isn’t that the point? Is that not your objective also?
        Listen mate, you brought this on yourself when you wrote this original post. Did you not expect any debate about it? A backlash like you have gotten?
        Of course you did, and you keep referring back to the original “scientifically proven” evidence that YOU provide to us because you ‘re a Pilot and an Weather Hobbist.
        Fair enough, but can we not ask questions here without being called idiots and trolls and whatever else you have called us questioners?
        That’s extremely disrespectful for a moderator of any Blog, Forum, Page, Channel, Social Network Sites …
        The most intriguing aspect about all of this, as I said, is why did you post this in the first place?

      • The calculations, Dec, please post your calculations. You’re not “asking questions”, you’re just trolling at this stage. I’ve always asked for scientific debate but have never received it, especially from you. Threats of a camera crew on my doorstep, name-calling, personal insults, ramblings from one side of the fence and then the other, that’s been the extent of your contribution.

        So – one last time – post your calculatons on how you arrived at 7300 ft so that you can gain back some bit of credibility. Also explain that bit about focal point and radar pixels because it makes absolutely no sense. If you don’t then I’m sorry but you’re still just like all the rest.

      • I sincerely hope you aren’t holding your breath, fergalt!
        Sadly this thread has now lost it’s way thanks to this behaviour. One of the major traits of a sociopath is constantly changing tack. They do it blatantly. Some people, during interaction with them, may think that there is something wrong with them the way they constantly and openly contradict themselves. But, what they are doing is striving for attention regardless of how much they contradict and lie, they know they are doing it, they just don’t care as long as they can convince people they are right. Once they have convinced people then they have control. The longer it takes him to get control over this subject the more he will come up with outlandish claims, ideas, suggestions and answers. As can be seen throughout the thread this has been the typical behaviour of all those posting in favour of chemtrails, they come up with the most mind-boggling and ridiculous claims, when asked for evidence they are affronted that anyone should dare to question them and they start attacking. Unfortunately there are some, like Dec, that just can’t provide sensible answers and hope to get by on incredibly silly claims, but their main fault is, they just can’t let it go.
        I can’t wait to hear his stunning answer!
        Have you noticed the grandiose claims beginning to reappear? He will take time out from the return journey from another of his photo shoots, down your way no less.
        On the one hand he has no problem turning my offer of help into me telling you how to run your blog, yet on the other hand he has no problem openly telling you that you aren’t running your blog properly. Two out of his last three replies are telling you you aren’t running it correctly, yet that should be OK, after all, he really does think he is more important.

      • I know he won’t come back with calculations because he made up that idea on the spur of the moment. He pretended to post a “fact” about pixels and radar, one which is complete gobbledegook, yet has now turned the comments back around on me for having the audacity to ask him for his evidence.

        All this, of course, after also playing our side of the argument a while back and rubbishing the chemtrail claims. He doesn’t know whether he’s coming or going, just like the Davoud Twohidys, Terry Lawtons, Max Bliss of this world. They know there are idiots out there that will latch onto their outlandish and fraudulent claims, but when questioned by the other 99% of level-headed individuals their only form of defence is attack.

        20 quid says he comes back here with a personal comment and not the calculations I asked for.

  2. US Patent 5003186 = seeding atmosphere for reduction of global warming (spraying with aluminum)



  3. The ‘Welsbach’ patent is well known, old (it’s patent has expired), and more importantly, there’s no evidence that it has ever been fitted, let alone used. But what if it had been used, it’s just a delivery system for a form of SRM. Geoengineering, if it ever happens, will be taking place in the stratosphere, and would not look like contrails, you sure as hell wouldn’t be able to see the aircraft, if they went that way. Balloons or rockets are as likely, as there are few planes that could fly to the required altitude.

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