When US air traffic was grounded for three days after September 11th, meterologists got a bit of a surprise. Apparently, airplane contrails—the high altitude trails of condensed water that form around tiny particles from engine exhaust—had a measurable effect on the climate. Researchers discovered that the absence of contrails expanded the difference between daytime and nighttime temperatures by a full degree Celsius, compared with the average of the last three decades. (More in this document).

In other words, not only do airplanes emit lots of climate-warming CO2, but their contrails may contribute to global warming as well. (See here for more on air travel’s climate impacts.)

Now, the L.A. Times is reporting on study by a British research team that found that the biggest contrail impacts come from nighttime flights during winter months:

“We get one-half of the climate effect from one-quarter of the year, from less than one-quarter of the air traffic,” said meteorologist Nicola Stuber, who led the English research team. “If you get rid of the night flights, you can reduce the climate warming effect of the contrails.”‘

The quick fix: a few schedule changes. A bit inconvenient, perhaps, but hardly inconceiveable.