A CLOUD, CREATED IN FLIGHT
Inside an aircraft trail.
Explore how invisible water vapour
becomes a visible cloud of ice.
Drag to orbit · scroll or pinch to zoom
Tracking view · distances compressedFROM ENGINE TO ICE CLOUD
Four moments in a contrail’s life.
Combustion produces water vapour, CO₂ and other emissions, including soot. Turbulent mixing cools and dilutes the exhaust. Water vapour itself is invisible.
What about “chemtrails”?
The scientific term for these aircraft ice clouds is contrails (condensation trails). “Chemtrails” commonly refers to claims of a secret spraying programme, for which there is no credible evidence. A long-lived or spreading trail is explained by atmospheric physics; its appearance alone does not establish chemical composition.
Aircraft do emit CO₂, nitrogen oxides and particles. Persistent contrail clouds can also warm the climate on average. Those real impacts are distinct from secret-spraying claims, and from documented activities such as agricultural spraying or cloud seeding. EPA overview ↗
How this model works & where it simplifies
Formation and survival are separate tests
We test whether a warm exhaust–air mixing line crosses liquid-water saturation. If it does in air colder than −38 °C, the model allows an ice contrail. Ambient relative humidity over ice then indicates whether growth can be sustained. RH over water is different: here it is 74%.
Ice saturation is a useful dividing line, not a lifetime forecast. Wake descent, entrainment, crystal loss, sedimentation and changing humidity matter.
Transparent assumptions
Jet fuel water emission index: 1.25 kg/kg; heating value: 43 MJ/kg; propulsion efficiency: 0.35; heat capacity: 1004 J/(kg K). Pressure follows a standard atmosphere; saturation pressures follow Murphy & Koop (2005).
Crystal sizes, numbers, plume width, wind shear and dissipation rates are illustrative. The scene compresses distance, enlarges the aircraft, and does not predict any real flight’s lifetime or climate effect. At exactly 100% RH over ice, no net growth from excess ambient vapour is assumed.
Sources & further reading5 references
Formation, persistence, patterns and aircraft emissions.
Definitions, environmental effects and “chemtrails” claims.
Aircraft and environmental limits on persistent contrail formation.
Murphy & Koop equations over liquid water and ice.
Formation and radiative forcing of contrail cirrus.