, so we could do the whole thing for about $100,000,000. Not too bad really.
Of course when we block and how much is hard, I'm sure the scientists will find a want to put a semi-pourous screen in solar-syncronous orbit.
Although the rising levels of acidity and CO2 in oceans is benefiting CO2->O2 and acidity absorbing bacteria and algae, so we might want to block out the sun over land in specific places. The Sahara, or Australian outback seem like good ideas (CHEAP arable land! WOO!) Australia has the advantage of being close to the worlds population center, so an extra breadbasket would be fantastic.
Of course the world's energy problems (mirrored solar, is gooood), food problems (recycling, and composting, more arable land... we really did urbanize the best farm land), and transportation problems will be improved as we like each other more and urbanize more densely and closer together (what is with the pressure differentials in condominiums, why is no one ever blasting rock music on their balcony [guess I'm young], and the dry air from the air vent!). Two of these seem to be happening a bit. It's hard to imagine a world where all three have happened so much that we want to scale them back, and I suppose that makes them good things.