Regardless of whether or not geoengineering actually does anything positive about climate change, it'll probably have some unintended consequences. Take, for example, this theory that geoengineering will bleach the sky.
Scientists have proposed injecting huge amounts of sulfate aerosols into the sky as a way of reducing the effects of climate change. These scientists also believe the particles could reflect away more sunlight, reducing the direct sunlight which reaches the earth by 20 percent. New Scientist writes:
The blue colour of the clear sky comes from light being scattering by molecules in the air. The scattering is much stronger for short blue wavelengths than for longer red wavelengths. Aerosol particles are much larger than molecules in the air, however, and they scatter red light more strongly, which washes out the blue light scattered by smaller molecules and makes the sky brighter and whiter.
Wow. So in an effort to save our blue planet, we may inadvertently turn it white. [New Scientist]