Global Alert News, August 24, 2019, #211 ( Dane Wigington)
How Airplane Contrails Are
Helping Make the Planet
BY FRED PEARCE
18 July, 2019
Contrails are human-made clouds. They form in air above about 25,000 feet, when that air is moist and colder than -40 degrees Celsius. Like regular clouds, they arise when water vapor, in this case from the engine exhausts, forms into droplets by condensing onto particles in the air, in this case soot from the engines. Within a second, the water droplets freeze to make tiny ice crystals that show up visually as contrails.
Bernd Kärcher, also of the Institute of Atmospheric Physics in Oberpfaffenhofen, reckons contrail cirrus clouds cover around 0.6 percent of the global skies at any one time — nine times the amount covered by contrails themselves. In areas with high amounts of air traffic, they can merge to cover as much as 38,000 square miles, roughly the size of Indiana, and last for many hours or even days.
The concern is not new. Patrick Minnis of NASA’s Langley Research Center reported more than two decades ago at a NASA meeting that vapor trails turned up on 40 percent of days over New York state, and later argued that “increased cirrus coverage, attributable to air traffic, could account for nearly all of the warming observed over the United States for nearly 20 years starting in 1975.”
During the day, cooling compensates part of the warming. But at night, with no sunlight, only the warming effect operates. Red-eye flights are a red light for climate. That’s the theory, and observational evidence backs it up. Research in the American South and Midwest has concluded that when contrails are around, they raise night-time temperatures sufficiently to reduce the day-night differences by 3 degrees C.
And after 9/11, when all commercial flights in the U.S. were grounded for three days, the diurnal temperature difference increased by up to 1.8 degrees C. The increase was strongest where air traffic was normally densest, said the study’s author, David Travis of the University of Wisconsin.
Even so, if done right, there could be a net overall reduction in warming. Volker Grewe of the Institute of Atmospheric Physics looked at 800 real transatlantic flights across the seasons and how their flight paths could have been altered to cut their combined warming effect from both contrails and CO2. He found that there could have been a 10 percent reduction in warming for only a 1 percent increase in operating costs.
that less soot would “strongly reduce” both the extent and lifetime of cirrus contrails.
The stakes are high. Left to their own devices, airlines are expected to increase global traffic four-fold by 2050. Improvements in engine performance will likely limit the increase in warming from CO2 to a factor of 2.4, Bock and Burkhardt predict. But even if fuel changes reduce soot emissions, they estimate that contrail production will increase by a factor of 2.8. This is enough, says Kärcher, to add as much as 0.1 degrees C to the global warming caused by contrails.