Why Airplanes Leave White Lines in the Sky
Tuesday, 2026/08/25196 words3 minutes2848 reads
When airplanes fly through cold and humid air, they often leave white lines across the sky. These are called condensation trails, or contrails. They form when ice crystals develop around soot particles released by airplane engines. The ice crystals create thin clouds that can trap heat in the atmosphere and contribute to warming the planet.
Not all contrails behave the same way. Some disappear within minutes, while others can last for hours and spread across large areas of sky. Scientists believe these longer-lasting contrails may have a climate impact, though there is still uncertainty about exactly how significant this effect is.
The UK and Google have launched a 30-month research program called Operation Blue Skies. During test periods over the next two winters, air traffic controllers will direct some flights over the northeastern Atlantic to change their altitude by up to 2,000 feet. The goal is to help planes avoid areas where contrails are most likely to form. Researchers expect around 10,000 flights to pass through the test airspace, with hundreds making route adjustments. The trial aims to determine whether small, safe changes to flight paths can effectively reduce contrail formation across an entire flight region.
