Engineering help needed

Is it really solid wood? Not some sort of laminated composite type of thing? You could put vertical braces up through the middle. Vertical bracing seems like the surest/easiest way to straighten it out. Or you could get some heavy duty corner braces and put them under the middle of each shelf. Something like this: Shop Stanley-National Hardware 8-in Zinc plated Corner Brace at Lowes.com -- not sure if this particular one would be strong enough, but you get the idea.

Or you could turn each shelf upside down if they're just on pegs (you wouldn't need to turn the whole bookcase upside down).

For what it's worth, though, in the pics you can hardly tell it's warped.