Over 100 years of contrails – a brief history
This photo was taken over Emden, Germany, on September 27th, 1943, by Stanley M. Smith.
1910s
The first contrails were observed over Munich, Germany, during WW I.
1930s
WW II began, and contrails became a war problem. The enemy could use the white lines in the sky to see where warplanes were headed, so both sides started researching what caused contrails to form.
1940s
A few years later, German scientist Ernst Schmidt discovered that high humidity and low temperatures cause contrails to form, but Germany kept it a war secret.
1950s
American Herbert Appleman published a paper explaining condensation trails to the public. Today, the discovery of what causes contrails is attributed to both men, and the Schmidt-Appleman criterion is still in use.
1990s
Scientists began studying the climate impact of contrails and how lingering contrails turn into cirrus clouds that reflect the sun’s heat during the day but trap Earth’s outgoing heat - especially at night. The significant net warming of contrails was established.
2010s
More researchers started working on methods to avoid making warming contrails and the idea of flying around the cold and humid areas to avoid contrails was explored in detail.
2020s
Contrail mitigation is now possible in real life and several companies and institutions are working to improve the solutions. It is time to implement the technology and scale it worldwide.