Chemtrails
Aircraft exhaust contains water vapour. At altitude, in humid enough air, it forms ice clouds that persist and spread. The variation people notice tracks humidity, not policy — and the atmospheric chemists best placed to detect a covert programme report finding none.
Why this verdict
Debunked by atmospheric physics that explains persistent contrails completely, and by a 2016 survey in which 76 of 77 independent atmospheric scientists reported encountering no evidence of a secret spraying programme.
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01The claim
That the long-lasting white trails behind high-altitude aircraft are not condensation but deliberately released chemical or biological agents, dispersed for purposes variously given as weather modification, population control, or sterilisation — and that their increase since the 1990s marks the programme's start.
02Where it came from
The term entered circulation around 1996–97, seeded partly by misreadings of a US Air Force academic exercise paper, Weather as a Force Multiplier: Owning the Weather in 2025, which was a speculative student assignment about hypothetical future capabilities and not a programme. Radio host Art Bell's late-night broadcasts carried it to a national audience, and it grew through the early web. A recurring supporting argument is that contrails did not persist in earlier decades — a claim contradicted by Second World War bomber photography, which shows long persistent trails, and by contrail research literature dating to the 1950s.
03What the record shows
✕ DEBUNKED — Investigated and refuted. Here is what actually happened.
Contrail formation is well-characterised physics. Jet exhaust adds water vapour and particulates to air that is already very cold, typically below −40 °C at cruise altitude. The Schmidt–Appleman criterion, formulated in the 1940s, predicts from ambient temperature, pressure and humidity whether a trail will form at all. Whether it then dissipates in seconds or spreads into a cirrus sheet lasting hours depends on the ice supersaturation of that layer of air. Two aircraft minutes apart at slightly different altitudes will therefore produce completely different trails — the observation most often offered as proof of spraying.
The engineering objections are decisive. Dispersing a meaningful quantity of any agent over a country requires mass: the payload capacity, refuelling infrastructure, dedicated tankage and personnel would be visible at every airport in the world, and no commercial aircraft has the spare payload to carry it while also carrying passengers and fuel. Material released at 10 kilometres disperses over hundreds of kilometres before reaching the ground, making targeted delivery impossible.
In 2016 Steven Davis and colleagues surveyed 77 atmospheric chemists and geochemists — the people who would find anomalous elements in deposition samples. Seventy-six reported having encountered no evidence of a secret large-scale spraying programme, and attributed the specific data points circulated by proponents, such as aluminium and barium in soil and water, to ordinary crustal abundance and known contamination pathways. Aluminium is the third most common element in the Earth's crust; finding it in soil is not a finding.
Solar geoengineering research is real, publicly funded and openly published. It is a proposal under active debate, not a deployed programme, and its researchers are among those most frustrated by the conflation.
04What it cost
Belief is substantial — around 10% of Americans have said it is completely true and a further 20–30% somewhat true. Consequences include harassment of atmospheric scientists, threats against a Harvard geoengineering experiment that was ultimately cancelled, and state-level legislative proposals to ban weather modification based on the premise. Sea-Spray and MKUltra are the reason this one is sticky: the government really did release substances over cities without telling anyone, which makes the leap feel shorter than it is.