Debunking Myth That Airplanes Fly Closer To Sun So It’s Hotter

People fly on airplanes daily. During my over thirty years as an atmospheric scientist, I periodically hear myths about the atmosphere, weather, and climate. One that periodically rears its head claims temperatures are warmer where airplanes fly because they are closer to the sun, so contrails could not possibly be forming. Let’s debunk that.

“Contrails are created when airplanes fly in cold and humid atmospheric conditions and ice crystals form around the particles emitted from the engine,” wrote the Federal Aviation Administration website. It went on to say, “They predominantly appear as white lines against the blue sky.” The term “contrail” means condensation trail. “Contrails are a type of ice cloud, formed by aircraft as water vapor condenses,” said NASA’s website. It continued, “The water vapor is already in the air surrounding the aircraft while the dust, or condensation nuclei, is comprised primarily of soot particles produced during the combustion process.”

While not exactly the same process, a similar analogue is seen from humans breathing on a cold day. Air from our breath encounters cold air outside of your mouth. The warm, moist air associated with exhaling is cooled enough to transform from a gas to small liquid droplets. In other words, breathing creates a little “cloud” on certain cold days.

Relatively speaking, the airplane flying at 28,000 feet is not much closer to the sun than we are on the surface since we are both roughly 93,000,000 miles from the star. However, there are some people that may think of it that way. Let’s explain why it is so much colder at cruising altitude than the surface.

We live within the troposphere. That is the layer closest to the Earth’s surface. “As the density of the gases in this layer decreases with height, the air becomes thinner,” said the NOAA website. Temperature is a measure of average kinetic or internal energy of a substance. The NOAA website continued, “Therefore, the temperature in the troposphere also decreases with height. As one climbs higher, the temperature drops from an average around 62°F (17°C) to -60°F (-51°C) at the tropopause.” This is why you often see snow-capped mountains even as the temperature is well above freezing at the surface.

Commercial airplanes fly within the troposphere at a typical cruising altitude of roughly 30,000 to 40,000 feet. That means temperature is likely between -40 and -95 degrees Fahrenheit. Ironically, there are some layers of the atmosphere that are relatively warm. The stratosphere contains the ozone layer which absorbs ultraviolet radiation from the sun.

Even higher up, there is a layer called the thermosphere. “Despite the high temperature, this layer of the atmosphere would still feel very cold to our skin,” noted NOAA’s website. Why so? “The high temperature indicates the amount of the energy absorbed by the molecules, but with so few molecules in this layer, the total number would not be enough to heat our skin,” it continued.