Talk about a vanilla sky. A scheme that would add light-colored, highly reflective particles to the atmosphere to reflect sunlight and cool the planet would significantly whiten the heavens, a new study suggests. Researchers analyzed the effect of adding enough aerosols to block 2% of the sun's light from reaching the ground, the amount needed to offset a carbon dioxide concentration twice that found in the air before the Industrial Revolution. (The approach is one of a series of so-called geoengineering efforts to tinker with the planet to mitigate the effects of climate change.) Depending on the size of the particles injected into the atmosphere, which would likely range between 0.7 and 0.9 micrometers in diameter, the aerosols' light-scattering effect would render the sky between three and five times brighter than it is now, the researchers report online today in Geophysical Research Letters. Most infrared wavelengths outbound from Earth wouldn't be strongly scattered by aerosols this size, so the particles wouldn't effectively trap heat in the atmosphere. But in visible wavelengths, the particles would tend to scatter more red light than blue, rendering the heavens whiter—in essence, giving the deep-blue sky now seen in remote areas such as Utah's Arches National Park (shown) the same hazy appearance often found in urban areas. Other side effects would include redder sunsets and brighter glows in the sky just after sunset—the same sort of phenomena seen after large volcanic eruptions, which spew large amounts of geological aerosols high into the atmosphere until natural processes clear the air.
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