FE has a direct relationship with the fuel you burn. keep it high and you save the earth to the best extent you can.
revving, screeching, burning out, harsh braking (because u did too much of accelerate in first place) etc add to pollutuon by scattering something or the other in the environment.
just in case, i wrote my ideas here.
http://www.team-bhp.com/forum/115273-post68.html (Does the fuel price hike affect your driving pattern?)