The other day I was crossing the harbor near where I live in a small ferry. I noticed numerous fresh jet contrails crisscrossing the sky. And then I noticed that many of the cirrus-like clouds were just older contrails that had dissipated. And I realized that it would have been a clear blue sky if it wasn’t for the jet traffic.
And today I looked up the term contrails and climate change on google.
In a recent study published in Nature Climate Change, Dr. Ulrike Burkhardt and Dr. Bernd Karcher from the Institute for Atmospheric Physics at the German Aerospace Centre show that the contrails created by airplanes are contributing more to global warming that all the CO2 that has been caused by the entire 108 years of airplane flight. Airplane contrails are the white clouds that we see in the sky spreading behind jets.
These cirrus clouds are created when the hot, moist air released from the plane freezes in the colder and drier air. These clouds then trap the long-wave radiation from Earth and create a warming of the atmosphere. In their study, Burkhardt and Karchar utilized satellite imagery of these spreading contrails to create a computer model which estimates how the contrails affect the Earth’s temperature. They have discovered that aviation contrails play a huge role in the impact on the climate and an even greater impact than that created by the CO2 emissions produced.
While the CO2 emissions from airplanes account for around three percent of the annual CO 2emissions from all fossil fuels and change the radiation by 28 milliwatts per square meter, the aviation contrails are responsible for a change of around 31 milliwatts per square meter.
Is this atmospheric graffiti a problem? Research by Penn State geography professor Andrew Carleton suggested it could be. Contrails “can extend the natural cirrus cover,” Carleton explained, and unlike most clouds, cirrus tend to warm the surface overall because they trap heat more than they reflect the sun’s radiation. “This is a concern to climate scientists because it could mean that a lot more contrails would make global warming worse.”
Although scientists had suspected that contrails affect regional temperatures, there was no way to truly test the idea until the terrorist attacks on Sept. 11, 2001. In the enforced no-fly period following the collapse of the World Trade Center, air traffic was completely stopped for three days and scientists were able to directly compare temperatures logged in the presence of contrails against temperature data collected with contrail-free skies.
“I remember walking to and from my office (during that time) and thinking how incredibly clear the skies were,” recalled Carleton. He mentioned this to a colleague and former doctoral-degree student of his, David Travis of the University of Wisconsin, who had noticed the same thing. “Then we started thinking that we should look at the temperature conditions” during those days in September and compare them to years past, Carleton said.
Looking at daytime highs and nighttime lows, Carleton and Travis found the average daily temperature range across the no-fly period to be almost 2 degrees Fahrenheit larger than when jets do fly. This implies, Carleton explained, that contrails lower daytime maximum temperatures and increase nighttime low temperatures — probably in the same way that cirrus clouds do, by blocking some solar radiation from reaching earth’s surface during the day and insulating against heat loss at night.