You are probably familiar with contrails — the thin, vaporous streaks of what looks like engine exhaust left in an airplane’s wake. What you might not realize, however, is that these vapor trails are not in fact engine exhaust, but artificially-induced clouds resulting from temperature and pressure disturbances airplanes create as they travel through the atmosphere.
Contrails generally arise in one of two ways, depending on atmospheric conditions.
- First, and most frequently, hot water vapor released as a by-product of jet fuel combustion comes into contact with cold air at high altitudes causing the water vapor to condense into visible, cloud-like contrails.
- Less frequently, pressure differences created by the wingtips of aircrafts traveling through extremely humid, water-saturated air can be great enough to induce water condensation and contrail formation. These pressure differences at the wingtips are called wingtip vortices, and their contrails look like this.
Again, depending on atmospheric conditions, contrails can either last a long time or dissipate quickly. In humid air, which allows contrails to hang around well after their creation, the initial water condensation can sometimes induce further water condensation, and even full cloud formation.
Scientists believe that increased air travel, resulting in increased contrail formation, is having a significant effect on global climate patterns. The high cirrus clouds that persistent contrails often resemble are known to trap the sun’s radiative energy, which has a net warming effect on atmospheric temperature. Whether this contributes to global warming is, like all things climate change related, up for debate. Interestingly, nearly all of the data linking contrails to global climate were collected in the three days following the September 11th attacks during which all commercial air travel was suspended over the United States, an unprecedented event in aviation history.