Chemtrails? It's ice.

Try it

Make a trail

Three things decide it: how cold the air is, how wet it is, and how much heat the engine throws away. Move them.

Air temperature Ice humidity Height Engine

Reading the chart. The gold curve is soaked air, measured against water. The pink dashes are soaked air measured against ice, which fills up sooner. Exhaust leaves the engine hot and wet, far up and to the right, and mixes into your air along the straight line. If the line pokes above the gold curve, droplets form and freeze at once: a trail. If your dot sits above the pink dashes, the ice has no reason to leave: the trail stays.

G = EI · c_p · p ⁄ ( ε · Q · (1 − η) )

Reading it: G is how steep the straight line is. EI is 1.23 kg of water per kg of fuel. cp is the heat it takes to warm air. p is the air pressure at the plane's height. ε is 0.622, how light water vapour is next to air. Q is the heat in a kilogram of fuel. η is the share of that heat that pushes the plane. At 34,000 ft this gives trails below -50.6 °C in bone-dry air and below -41.1 °C in soaked air.

One sky, three trails

Three planes, three heights

Each line is a plane at a different height, in its own layer of air.

Iamdev37 · CC BY-SA 4.0

Two jets side by side at one height: the upper one leaves a trail, the lower one none

A test flight, 2000

The better engine makes the trail

German researchers flew an Airbus A340 and a Boeing 707 wing by wing, at the same height, in the same air, and watched from a third plane. The A340, with its more efficient engines, left a trail. The 707 left none. An engine that turns more of its heat into push sends out cooler exhaust with the same water in it, so it reaches saturation sooner.

Weigh it

Could a plane carry it?

3.6 kgwater out of the engines, per km

7,650 kgice in that km an hour later

×2,151came out of the sky

2.6 kmof trail a full 20 t payload could fill

Two squares with areas in proportion: 7,650 kg of ice against 3.6 kg of engine water

A narrow-body jet burns about 2,400 kg of fuel an hour and makes 3.6 kg of water for every kilometre it flies. An hour later, a spreading trail can be 2 km wide and 500 m deep. At −50 °C with the air 20% past ice saturation, each cubic metre gives up about 8 milligrams of ice to the crystals the plane left behind. Multiply: 7,650 kg of ice in that kilometre. The engines supplied 3.6 kg. The sky supplied the rest.

A tank could not do this. An airliner's whole payload, about 20 tonnes, would fill 2.6 km of that trail. The IPCC put it plainly in 1999: a new trail's ice grows to exceed the plane's water “by more than two orders of magnitude”.

Manchester, 2008

Old trails, spreading

Hours-old trails fan out into thin cloud. The air was already holding more water than ice can stand.

Anthony Appleyard · public domain

Bearings

Grids, X's and stripes

Three air routes crossing, each trail older, wider and further downwind than the one after it

A trail points the way the plane was going. You can read its bearing off the sky.

Airliners fly set highways in the sky, called jet routes, between 18,000 and 45,000 ft. Two routes crossing make an X. One busy route makes parallel stripes a few minutes apart. The wind pushes every stripe sideways, and each stripe is a different age, so each has moved a different distance: the oldest is widest and furthest downwind. A criss-cross sky is a day when the air is wet enough to keep every trail. The picture above is drawn from that rule alone: three routes, a plane every half hour or so on each, a steady wind.

From space, 15 Feb 2013

The whole sky's worth

Trails over Spain and Portugal from NASA's Terra satellite: the jet routes, drawn in ice.

NASA Goddard / MODIS · public domain

27 September 1943

Trails before jets

B-17s of the 390th Bomb Group over Europe, their fighter escorts looping trails above them. Piston engines breathe out water too.

Sgt. Stanley M. Smith, USAAF · Smithsonian NASM · public domain

NaN asks, Beer answers

Questions

NaNWhy does one plane leave a long trail and the next plane none?

BeerThey are at different heights, and wet air comes in layers. The panel above shows three heights; they often disagree. The engine matters too: see below.

NaNThey didn't use to last this long.

BeerThey did in 1943 (the bombers above). There are more planes now: 153,359 commercial flights on 23 July 2026, a record day. And newer engines make trails in warmer air.

NaNWhat about the photos of barrels inside planes?

BeerWater ballast for test flights. Boeing's photo archive labels them so. On the Airbus A350 test plane each barrel holds about 300 kg of water, pumped fore and aft to move the balance point.

NaNSoil tests found aluminium and barium.

BeerAluminium is about 8% of the Earth's crust, the most common metal in it. Barium runs about 628 parts per million. Any soil test anywhere finds both.

NaNThere are patents and papers about spraying the sky.

BeerThere are. They are ideas on paper. The designs put the spray near 20 km up, higher than airliners fly, from a plane that has not been built. Harvard's one planned balloon test was dropped in March 2024 before it flew.

NaNThe Air Force wrote about owning the weather.

BeerA 1996 student paper imagining the year 2025. Its front page says it holds fictional scenarios and is not Air Force policy.

NaNWeather modification is real, isn't it?

BeerYes. Thailand's royal rainmaking has flown since 1969: salt near cloud base, dry ice below it, silver iodide at the tops, up to about 21,500 ft. It seeds clouds that are already there. A trail at 35,000 ft in clear blue sky is something else.

NaNWho else says so?

BeerIn 2016, 77 atmospheric chemists and geochemists were asked. 76 had seen no evidence of a secret spraying program. In 2025 the US EPA, under an administrator who took the question up, wrote that it knows of no trail ever made on purpose for weather over the US.

NaNSo do trails matter at all?

BeerThey do, for warmth. Trail cloud holds heat in: about 57 of aviation's 101 milliwatts per square metre of warming in 2018, more than its carbon dioxide. Airlines now test steering around trail-making air. That is the trail story worth talking about.

NaNHow do I settle it myself?

BeerMake a prediction. Read the panel at the top, write down "long trails at 3 pm", then look up at 3 pm. A spraying program would not follow tomorrow's humidity forecast.

Over the wing

Trails from wings

Air speeding over a wing drops in pressure and cools, and wet air makes a brief cloud. Gone the moment it leaves the wing.

Andrey Filippov · CC BY 2.0

Send this instead of arguing

nanobotco.github.io/chemtrails

Sources

Photographs from Wikimedia Commons, credited on each. Drawings and code: NaNoBotCo. NaN and Beer drawn by NaNoBotCo.

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