SOURCE: Science

DATE: June 28, 2019

SNIP: The aviation industry has long been criticized for its large environmental footprint, particularly its climate-warming carbon emissions. But a new study suggests that another byproduct of airplanes—the white contrails they paint across the sky—has an even bigger warming effect, one that is set to triple by 2050.

Planes create their mesmerizing contrails as they soar high in the thin, cold air. Water vapor quickly condenses around soot from the plane’s exhaust and freezes to form cirrus clouds, which can last for minutes or hours. These high-flying clouds are too thin to reflect much sunlight, but ice crystals inside them can trap heat. Unlike low-level clouds that have a net cooling effect, these contrail-formed clouds warm the climate.

A 2011 study suggests that the net effect of these contrail clouds contributes more to atmospheric warming than all the carbon dioxide (CO2) produced by planes since the dawn of aviation. And those effects are predicted to get worse as air traffic—and the resulting cloud coverage—increases: Some estimates suggest global air traffic will quadruple by the year 2050.

The researchers modeled the effect of global contrail cloud coverage in 2006, a year for which they had accurate aviation data. Then, taking into account predictions for future air traffic and emissions, they modeled the effect of contrail clouds for 2050. They found a threefold increase in their warming effect over that time, they report this week in Atmospheric Chemistry and Physics.