[Renegade 13]

Jack Simth said:
1) Sunlight is what causes global warming. It's also what feeds plants. Cut down on the sunlight, and there's issues with little things like O2 production.

As Will mentioned above, this can be averted by having a system that is only blocking sunlight part of the time; I was thinking blocking say half an hour of sunlight per day around the world. On a side note, I bet that that half hour of darkness would be absolutely pitch black. Probably couldn't see an inch in front of your face without other lights!

Jack Smith said:
2) Space is kinda hostile. Millions of very small meteors hit the Earth regularly. Most simply burn up in the atmosphere. This thing would have to be outside the atmosphere - it would be liable to get cut to ribbons.

Now this I hadn't thought of, and it'd be a little tough to get around. Though now that I think about it, how does the ISS avoid micrometeorite punctures? Sure, you can map those in Earth orbit, but what about those that come in from elsewhere? Not sure of a solution to this one.

Will said:
3) Good God, do you realize how much time, energy, and money it would take to build such a thing? Even beyond the huge engineering problems of preventing the thing from falling apart from constant meteor and space-junk impacts, we still have barely progressed beyond Apollo-era space technology. And some would say we have regressed to pre-Apollo technology, by swamping everything in more complexity. And you're proposing to create something that massive?

Well, I'm not saying it would be easy or cheap! Though it may be cheaper than all that will be necessary to prevent further climate change and to effect a reversal, I'm not sure. There would definitely be absolutely massive engineering challenges, but I don't think it would entail anything fundamentally beyond our technology level.

Will said:
4) As a corollary, the time, energy, and money that would need to be poured into such an endeavor would have a much bigger impact if put into, say, infrastructure to reduce current emissions of carbon dioxide, and/or methods of recapturing carbon, research into sustainable energy like fusion, and growing enough food to feed every person on Earth.

I'm not sure if the money would be better spent funding other methods of halting and reversing climate change (which I'm not sure is even possible), since the shield would essentially do the same thing that all the environmental efforts are aimed at.