One idea I have heard of is putting a large Space Blanket kind of mylar at L1 out in space to keep the sun from hitting earth so much

 It would basically be a permanent eclipse effect in order to stop the sun from hitting the earth so much.

However, I'm not sure how you would decide what areas you want shaded?

Because the Mylar would be stationary and block the same point while the earth turned. So, you might have the effect of one area (all around the earth 360 degrees) where the sun never hit?) because as the earth rotated in relation to the sun it would hit the same different points 24 hours every single day. But, as the sun rotated on it's axis it would also hit different points on the planet as the planet changed seasons?