Blocking the sun light on a global scale sounds like something straight from some scifi story, but that's exactly what Bill Gates wants to do to save us from the global warming. The first thing that comes ro mind from such idea is some huge objects floating in space between the Earth and the sun. Of course that would require huge megastructures to be effective. The solution needs to be much closer to be feasible to our current capabilities and resourses.
The proposed solution is indeed much more simple and closer than some structures in space. The idea is to scatter calcium carbonate into our atmosphere that could reflect some of the sunlight back to space. Just like the ozone layer the greenhouse gasses are destroying.
Sounds great and simple... and scary. We have no idea what effects such tampering of our atmosphere would have on the long run. Also what would happen if we get our emissions under control and the ozone layer starts recovering while this sun blocker is still up there? Or what if we, saved by this, don't learn anything and just keep consuming more without giving a thought on the next ecological crisis before it's again too late to act?