Instead, what they are are soot particles and frozen water vapor, which are both common byproducts of a jet’s combustion engine. According to Stephen Barrett, a professor of engineering at Cambridge University who focuses on the effects of aviation on the environment, “a contrail is an artificial cloud.” He told Popular Science, “They’re pretty much the same as natural cirrus clouds, except they’re initially long and straight.” Additionally, contrails are negatively impacting the world, despite the unfounded rumors that planes are spreading substances that give people mind control.
How do clouds of contrails form?
Even though they are as basic as dust and water vapor, contrails don’t always form or stay in the wake of an aircraft. For the jet vapor to crystallize, the atmosphere must contain the ideal balance of moisture to prevent evaporation and coldness to cause freezing. According to Barrett, “air that is cold enough or humid enough is called ice supersaturated.”
At ordinary commercial aircraft cruising altitude (about 35,000 feet up), ice supersaturation is rather common compared to other atmospheric heights. However, he continues, it only occurs five to ten percent of the time.
Conditions also affect how long a contrail lasts, or how long its “persistence” lasts. In general, contrail clouds disintegrate quickly in warmer, drier air, but Barret notes that the correct combination of moisture and cold can cause them to remain in place for up to six hours and spread widely across the sky.
According to Marc Stettler, an Imperial College London professor of transport and environment, contrails differ by season and location because they are so strongly correlated with temperature and air moisture content. According to Stettler, they are more frequently seen in numerous locations in the spring and fall.
Are contrails harmful?
Sort of, albeit probably not in the way you might anticipate and unrelated to human health in any way. An increasing amount of scientific data, including studies by Barrett and Stettler, suggests that contrails together have a warming effect that contributes to climate change brought on by human activity.
Naturally, flying an airplane releases carbon dioxide into the atmosphere and burns fossil fuels, which contributes to climate change. However, the thermal effect of contrails is not the same as the greenhouse gas emissions from flight. And the effect is shockingly strong.
Barrett claims that, with one important exception, “the contrails from aviation cause about as much warming as all the CO2 from aviation.” Contrails are transient, disappearing within a few hours, yet flying generates cumulative carbon emissions that build up over decades. Thus, the last six hours of contrails have contributed to almost the same amount of global warming as the last 60 years of CO2 emissions from aviation. It’s a rather potent lever, he claims.
Put another way, according to Stettler, contrails account for about two percent of all the warming that humans produce in a given year, which includes everything from greenhouse gas emissions from cars to agricultural practices to home heating. Even while two percent might not seem like much, sources predict that over the next 30 years, commercial aviation traffic will increase by a factor of 2.5. After all, when the planet is at stake, everything matters.
How warm the climate are contrails?
Contrails reflect light and heat but also trapping it because, like other clouds, they are dazzling white and insulating. A contrail accomplishes two tasks at once on a sunny day. According to Barrett, it “acts like a blanket,” preventing heat emanating from the Earth’s surface from escaping into space. This causes warming. In addition, it has the cooling effect of reflecting sunlight from space away from Earth’s surface. Barrett laments that, even in bright light, the blanket effect usually dominates the reflector effect.
And there’s no competition after the sun sets. There are no space rays for contrails to reflect at night; instead, they are confined by heat. Even though contrails are transient, after the original obstruction is removed, the heat that they reflect to the surface of our globe doesn’t magically disappear. Furthermore, there are so many aircraft in the sky at once that, under ideal circumstances, there will likely be a new contrail in place to replace the one that has dispersed.
How can we resolve it?
According to Barrett, ice supersaturated regions can be quite broad bands across the atmosphere, but they are frequently very thin, so pilots can avoid them by flying just above or below the areas where contrails are most likely to form. It’s often only a thousand feet or so of adjustment, which is “quite small relative to cruise altitudes,” he continues. Stated differently, a small adjustment to the flight path could have a significant impact.
According to Stettler, our ability to predict atmospheric conditions at 35,000 feet is currently lacking. He says, “There isn’t a lot of data for it, and meteorologists haven’t made it a top priority.” However, scientists are trying to make it better so that we can forecast the weather and schedule flights appropriately. Barrett suggests that reducing the worldwide impact in the interim may be achieved by simply reacting to conditions in real time, as pilots presently do, to minimize turbulence, and by lowering altitude as soon as a contrail becomes apparent.
There have already been a few small-scale forecasting studies conducted, one of which involved Google, Breakthrough Energy, and several airlines. Barrett points out that more extensive research is necessary to determine the most effective way to reduce contrails. “We really need to go after that—let’s say all of the Scottish airspace or a significant portion of the Atlantic tracks—because that is the next challenge.”
However, Stettler points out that more work needs to be done by the aviation sector even if we manage contrails. According to him, “actions to mitigate aviation’s CO2 emissions should not be substituted or replaced by reducing the effects of contrails.” After all, there would still be decades’ worth of residual emissions to be concerned about even if all the contrails vanished in a single puff.