For those who live under a well-liked plane route, you are probably no stranger to long, thin clouds within the sky. These are contrails emitted from airplanes.
Contrails, or condensation trails, are essentially human-made clouds; they’re trails of condensed water vapor created by jet engines, in response to the National Weather Service.
We mostly see them behind planes at cruising altitude, but they will also be emitted by rockets.
How do contrails form?
Contrails are created when the new water vapor emitted by a jet engine after combustion cools and condenses in Earth’s atmosphere, in response to the Environmental Protection Agency (EPA). The atmosphere’s temperature and humidity should be in only the fitting place for condensation to occur — the air should be cold with some humidity.
Contrails mostly form at an airplane’s cruising altitude, between about 32,000 and 42,000 feet (10,000 to 13,000 meters) within the upper troposphere, per the Rocky Mountain Institute (RMI), because that is where those conditions are found. Since the atmosphere is ever-changing, conditions may not be right for contrail formation at this altitude, which is why not all airplanes create contrails during every flight.
Contrail FAQs
Are contrails good or bad?
Generally speaking, contrails are neither good nor bad. They’re simply a cloud created by jet engines under certain atmospheric conditions. That said, research suggests that contrails contribute to atmospheric warming and cooling, in response to RMI, and the warming, specifically, is an issue for the planet.
Why are contrails bad for the environment?
Contrails that form at night or last into nighttime are the major contributors to atmospheric warming, per the Rocky Mountain Institute (RMI). Earth undergoes radiative cooling at night — heat radiates from the surface into space — but clouds like contrails can trap that heat.
Why are they called contrails?
Contrail is a portmanteau of “condensation” and “trail.” Contrails are trails of condensation created by jet engines at cruising altitude within the atmosphere.
Why do some planes not produce contrails?
All jet engines can potentially produce contrails, but specific atmospheric conditions are required for contrail formation, per the National Weather Service. The air must be each cool and humid — conditions which might be mostly found at cruising altitude.
How long do contrails last?
If a contrail forms behind a plane, it might last just seconds before dissipating, or it will possibly last hours. All of it will depend on the atmospheric conditions on the time, in response to the EPA; lower humidity results in short-lived contrails, while higher humidity results in persistent contrails. Within the latter case, contrails may then be unfolded by the wind, reaching a number of miles wide and 650 to 1,300 feet (200 to 400 m) high. We are able to accurately predict whether a contrail will form based on the atmospheric temperature and humidity, the EPA says.
Are contrails dangerous to humans?
No, contrails are usually not directly dangerous to humans. There may be a conspiracy theory that the federal government uses aircraft to disperse toxic chemicals into the atmosphere for quite a lot of nefarious reasons, creating chemical trails, or “chemtrails,” that look just like contrails. Nonetheless, there isn’t a evidence to support this scenario.
“There isn’t any basis to the conspiracy, and scientists don’t consider it as in any respect credible,” Steven Barrett, the H. N. Slater professor of aeronautics and astronautics on the Massachusetts Institute of Technology (MIT) and director of the MIT Laboratory for Aviation and the Environment, told Space.com
David Keith, a professor of applied physics at Harvard’s School of Engineering and Applied Sciences and a professor of public policy on the Harvard Kennedy School, provides a detailed debunking of the idea on his research group’s website. Keith studies climate science and technology, in addition to public policy of solar geoengineering.
Environmental effects
Contrails are comprised of water vapor, similar to clouds are. Although contrails and clouds are usually not outwardly dangerous to the environment, they do play a task in Earth’s temperature regulation via the greenhouse effect. Per NASA, clouds — including contrails — can have each cooling and warming effects on our planet. The sun emits thermal radiation that travels toward Earth. When solar radiation reaches thick clouds in Earth’s atmosphere, those clouds can reflect the radiation out into space, keeping the planet cool. But when the radiation does reach Earth’s surface, the planet itself reflects solar radiation out into space at night — unless there are thin clouds like contrails within the night sky. Those clouds can trap the reflected solar radiation and warm Earth.
The difficulty is just not the short-lived contrails but quite the long-duration ones that stretch over a big area and, in effect, develop into cirrus clouds, that are a significant offender in trapping heat on Earth, per the National Weather Service.
Several private and non-private entities are currently researching ways to mitigate contrails’ effect on the climate. For instance, a study by NASA and DLR (the German Aerospace Center) revealed that sustainable aviation fuel can reduce contrail formation by 50% to 70%.
Contrail Q&A with an authority
We asked Steven Barrett, a professor of aeronautics and astronautics at MIT and the director of the MIT Laboratory for Aviation and the Environment, a number of often asked questions on contrails. Barrett researches the ways aviation can achieve zero environmental impacts.
Steven Barrett is a professor of aeronautics and astronautics at MIT, an interim department head of the Aeronautics and Astronautics Department, and director of the MIT Laboratory for Aviation and the Environment.
Can every kind of airplanes create contrails?
No, typically only jet aircraft fly high enough to be within the coldest a part of the atmosphere where contrails can form. It’s typically coldest around 35,000 feet [11,000 m]. Below that, it gets warmer as you approach the bottom, and above that, the atmosphere gets warmer attributable to the ozone layer absorbing UV radiation from the sun.
What atmospheric conditions affect the formation and longevity of contrails?
It needs to be cold enough and humid enough for the water emitted by burning fuel to freeze into what is basically an ice cloud. The contrails can last hours if those conditions persist, but lifetimes vary a fantastic deal. Much of the time, a short-lived contrail forms where it isn’t cold or humid enough for it to freeze. Often, you’ll be able to see these short-lived contrails behind airplanes, but they don’t seem to be of concern relating to the climate.
Do contrails have any effect on humans? What concerning the climate?
They haven’t got a direct impact on humans but do contribute to climate change and so have an indirect effect. Contrails reflect incoming sunlight and trap outgoing heat, with a net warming effect that is just like the warming from aviation’s CO2 emissions.
Additional resources
See photos of several types of contrails from the GLOBE (Global Learning and Observations to Profit the Environment) Program. Learn the way contrails affect the climate from the Yale School of the Environment. Discover how AI can mitigate contrails’ impact on climate in this text from Google.
Bibliography
Aircraft Contrails Factsheet. Environmental Protection Agency. Retrieved Aug. 18, 2023, from https://nepis.epa.gov/Exe/ZyPDF.cgi/00000LVU.PDF?Dockey=00000LVU.PDF
Cathcart, J. and Andrew Chen. Contrail Mitigation: A Collaborative Approach within the Face of Uncertainty. Rocky Mountain Institute. Retrieved Aug. 18, 2023, from https://rmi.org/contrail-mitigation-a-collaborative-approach-in-the-face-of-uncertainty/.
Clouds and Contrails. National Weather Service. Retrieved Aug. 18, 2023, from https://www.weather.gov/fgz/CloudsContrails
How Do Clouds Affect Earth’s Climate? NASA Climate Kids. Retrieved Aug. 18, 2023, from https://climatekids.nasa.gov/cloud-climate/
Keith, D. Chemtrails Conspiracy Theory. David Keith’s Research Group. Retrieved Aug. 18, 2023, from https://keith.seas.harvard.edu/chemtrails-conspiracy-theory
Weather in Motion: Contrails. National Weather Service. Retrieved Aug. 18, 2023. https://www.weather.gov/bgm/WeatherInActionContrails