Contrails make clouds brighter, according to new study

Most of us are familiar with the cloud-like vapor emitted by many aircraft or condensation trails, also known as contrails as we often see them appear behind the tail end of planes as they linger in the sky. Contrails form when the water in the jet exhaust mixes with the cold, wet air in the sky and then condenses into ice crystals to form a type of cirrus cloud, and this cirrus cloud is what we identify from the ground as a contrail.

Scientists and aviation experts have known for a long time how these contrails form, but it was only until last summer that a new study published in Nature Communications, found that the cirrus clouds formed as a result of the contrails actually become brighter once a plane passes through them.

In other words, the study found that contrails which linger in the sky and are then passed through by planes then become brighter as they reflect more sunlight into space. So how did the atmospheric scientists determine this brightness effect in contrails? As it turns out, largely with the aide of satellites and computer models to measure the data.

How are the contrails able to make clouds brighter?

Well according to the 2016 study, it is the particles of soot which are emitted by the engine of the aircraft that act as the magnet around which the cloud continues to grow. The ice crystals of the cirrus cloud then increase in number, which results in an increased surface area for the sunlight to then bounce off of. This reflected sunlight manifests in the clouds as brightness.

Further analysis revealed even more information behind why certain cirrus clouds are more likely to produce this apparent brightness effect. Laser-radar instruments used to measure the physical properties of the clouds show that the closer the contrails were the aircraft they were emitted from, the thicker they were, and thus all the more likely to create the brightness effect.

Why is the appearance of brighter clouds significant? 

Now that this recent study has documented evidence showing how contrails behave in certain atmospheric conditions, why is it significant that contrails can make clouds brighter in some instances? Believe it or not, this study has implications for the ‘global climatic effect of contrails’, which means that this can improve our overall understanding of how the aviation industry is affecting climate change.

So the reflectivity (i.e., the brightness) of the cirrus clouds demonstrates how according to one of the study’s authors, Matthias Tesche, “It won’t make up for all the CO emissions, but this discovery assists the general cooling effect of contrails and will need to be factored into assessments of the impact of aviation on the climate” ( 

Ideally, the continued research on the properties and effects of contrails will advance our overall knowledge on the important role of aviation in the age of climate change.