If you go outside on a clear day and look up toward the sun—being careful to block out the bright disk with your thumb—you might see a hazy white region surrounding our star.
This haze is caused by airplanes, and it is gradually whitening blue skies, says Charles Long of NOAA’s Earth System Research Laboratory in Boulder, Colorado. “We might be actually conducting some unintentional geoengineering here,” Long said at a press conference this week at the American Geophysical Union Fall Meeting in San Francisco.
Geoengineering involves the manipulation of an environmental process in such a way, usually deliberate, that it affects the Earth’s climate. For instance, previous researchers have proposed combating global warming by intentionally seeding the atmosphere with small particles, or aerosols, to scatter some sunlight and reduce the amount of heat trapped by greenhouse gases.
Long and his colleagues don’t yet have enough data to know how much of an effect the icy haze left by airplanes may be having on the climate or whether it is contributing to warming or cooling. But its existence demonstrates yet another way that humans might be altering the climate system, Long says, and “you can see this with your own eyes.”