Dawn Stover writes:

Those wispy stripes left behind by airplanes have a surprisingly forceful, albeit short-lived, effect on the climate. After accounting for factors such as aircraft improvements that are expected to reduce soot emissions, climate researchers at the German Aerospace Center recently estimated that the heat-trapping effects of cirrus cloudiness caused by contrails will “increase significantly over time” because of the large projected increases in air traffic—which is growing so fast that efforts to make airplanes less polluting won’t be able to keep up with the growing effects of contrail clouds. Contrails might also have indirect effects, which are still unclear, on other clouds and on wind patterns.

Scientists have long known that contrails can affect regional climate. The empty skies during the three days after 9/11, when all commercial airliners were grounded, allowed for an unintended experiment showing that contrails mimic the effects of normal clouds.

The contrail-climate connection may have unintentionally bolstered a conspiracy theory: that the government is trying to manipulate the weather by laying down suspiciously gridded “chemtrails.” The theory relies on a fundamental misunderstanding of how contrails form and how long they can persist in the atmosphere. For example, many people are not aware that planes and ships (which also leave tracks in the sky) travel along well-defined traffic lanes, often at regularly spaced intervals, which can create distinctive patterns of parallel lines. A 2016 survey of scientists with expertise on contrails not only debunks the “chemtrail” conspiracy but also demonstrates how photos and other data cited by conspiracy theorists can be explained by well-understood physics and chemistry. [Continue reading…]