Contrails – short for condensation trails – are linear clouds made up of ice crystals that form behind jet aircraft at high altitudes. These artificial cirrus clouds are formed when hot and moist aircraft exhaust meets cold and humid ambient air. Water vapor in the exhaust condenses on particles that originate from soot in aircraft exhaust.
A long-standing (and thoroughly debunked) conspiracy theory posits that contrails are actually toxic chemicals being deliberately sprayed for a variety of nefarious purposes that include population control, mind control, biological warfare, or weather modification.
A recent study by Chalmers University in Sweden looked at the climate impact and social costs of contrails. While contrails are by no means a threat, they can have a negative impact. In particular, these short-lived clouds do contribute to the global warming impact of aviation.
Aviation contributes about 2.5% of global carbon dioxide emissions. Contrail cirrus has both warming and cooling effects because the clouds absorb infrared radiation – a warming effect – and scatter solar radiation – a cooling effect.
Overall, the study found that contrails can add to aviation’s warming effect by as much as 25% of the impact of its carbon dioxide emissions. They suggested some mitigation strategies for reducing the effects of contrails including ways to reduce soot emissions as well as rerouting of flights to avoid regions where contrails are more likely to form.
