Jet engines burn fuel and expel hot, water-laden exhaust. At cruise altitude — typically 30,000–40,000ft — air temperatures hover around −50°C to −60°C. The exhaust freezes almost instantly into tiny ice crystals. That white line is ice, full stop. No mystery ingredient.
This is the question chemtrail believers get wrong. Whether a contrail lasts seconds or spreads into a wide hazy sheet depends almost entirely on relative humidity at cruise altitude — specifically whether the air is ice-supersaturated. High humidity = ice crystals persist and grow. Dry air = ice sublimates back to vapour in seconds. Same plane, same fuel, completely different result depending on the air mass it flew through.
Each time slot predicts what contrails are expected to do, using relative humidity at 200hPa (~39,000ft), 250hPa (~34,000ft) and 300hPa (~30,000ft), wind speed at altitude, and temperature. Wind speed drives spreading — strong jet stream winds shear trails sideways into wide cirrus sheets, while calm upper air keeps even persistent trails as narrow lines.
The forecast shows yesterday, today, and the next 5 days as a single continuous timeline. Past slots are dimmed. The current time slot is highlighted with an amber border and a NOW marker. Future slots are fully lit. A dividing line separates past from future.
Yesterday's slots are always visible at the top. If someone points at trails they saw and claims something suspicious, scroll up and show the RH reading for that time. If trails were predicted and appeared — that's physics, not conspiracy.
Yes — and this is legitimate science, openly researched and published. Contrails trap outgoing heat from Earth's surface, similar to how CO2 does, while also reflecting some incoming sunlight. The net effect is warming. Current estimates suggest the warming from contrails is broadly comparable to aviation's CO2 emissions — so they roughly double aviation's climate footprint, though with significant uncertainty.
Crucially, only around 2–3% of flights are responsible for about 80% of the warming effect, because persistent spreading contrails require specific atmospheric conditions. This is why airlines and researchers are actively trialling contrail avoidance — rerouting flights around ice-supersaturated layers, exactly as they avoid turbulence. The complication is that avoidance burns more fuel, so each decision has to show a net climate benefit.
Recent 2025 research has complicated the picture further: more than 80% of long-lived contrails form inside existing cloud layers rather than clear sky, which may reduce or even reverse their warming effect in those cases. The science is actively evolving. Far from a secret — contrail climate impact is one of the most studied areas in atmospheric science right now.