The greenhouse effect is trapping the heat, not the light. So sunlight hits the atmosphere, some reflects, some more reflects off of the surface and back out, a

The greenhouse effect is trapping the heat, not the light. So sunlight hits the atmosphere, some reflects, some more reflects off of the surface and back out, and the rest is involved in various things that eventually results in heat. That heat can then radiate out, or be trapped. Our problem is the balance of heat radiating out vs being trapped is changing. If we jump right to stopping the sunlight in the first place, sure it'll reduce the amount of heat that is produced thereby reducing the amount of heat trapped in the atmosphere, but that's not the only thing we need to consider.