It's a general question, I'm not sure I'm able to help a lot (actually I'm not sure I understand it, I think it's pretty much a consensus that ride sharing reduces carbon dioxide emissions).
Anyway:
This page (and the whole website, actually) looks very good.
Maybe this one could help.
And if you're looking for people, there's a Facebook application called "Carpool" which has 943 daily active users -- I suggest you join them and hear their ideas and opinions.
Good luck!
