Geoengineering would turn blue skies whiter New Scientist ^ | 6/1/12 | Jeff Hecht Geoengineering would turn blue skies whiter - environment - 01 June 2012 - New Scientist Blue skies would fade to hazy white if geoengineers inject light-scattering aerosols into the upper atmosphere to offset global warming. Critics have already warned that this might happen, but now the effect has been quantified. Releasing sulphate aerosols high in the atmosphere should in theory reduce global temperatures by reflecting a small percentage of the incoming sunlight away from the Earth. However, the extra particles would also scatter more of the remaining light into the atmosphere. This would reduce by 20 per cent the amount of sunlight that takes a direct route to the ground, and it would increase levels of softer, diffuse scattered light, says Ben Kravitz of the Carnegie Institution for Science in Stanford, California. That would have knock-on effects for life and human technology. The reduction in direct sunlight would impact the solar industry, which relies on direct sunlight to generate much of its power. But the increased indirect sunlight would boost photosynthesis beneath tree canopies. The most visible effect, though, would be above us. 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.