Right now it sounds like Sci-fi but the proposal is already being bandied about. LiveScience ran an article ten years ago. The idea is to launch millions of tiny space umbrellas into orbit around the equator to block the sun's rays, to help cool the oceans.

Here's the link:

http://www.livescience.com/3880-space-ring-shade-earth-stop-global-warming.html

This is a very cool rendering of what a solar shade ring would look like from the earth.

http://imgur.com/a/LdGmN?gallery