When U.S. air traffic was grounded for three days after September 11th, meterologists got a bit of a surprise. Apparently, the lack of airplane contrails — the high altitude trails of condensed water that form around tiny particles from engine exhaust — had a measurable effect on the climate. (More in this document.) Apparently, contrails reflect sunlight during the day, but also trap heat at night. On net, researchers believe that contrails can have two to three times as much climate-warming power as the CO2 emitted in airplane exhaust.

Now, the L.A. Times is reporting on a study by a British research team that found that the biggest contrail impacts come from nighttime flights (when contrails reflect solar radiation back to the earth’s surface) and 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 inconceivable.