There are probably better ways to block out the sun. Glass is heavy and would cause a lot of problems. Something that floats high in the sky would be better, but it would unfortunately move with the wind and weather. If you could get something big enough to space, in a geosynchronous orbit, it just might work…
What would happen if we put a giant glass tinted dome over each city?
In this scenario, we aren’t trapped in the dome. There are openings and doors, so we can get out, cycle in fresh air, etc....