nepkanchi,
As I read it, the Peace prize is for those who manage to create a change in the society by some form of influence. It is to bring together people in some sense.
He did it through his work in environment...he brought (at least tried) everyone together on this one...something towards peace and harmony in the society?
You need not necessarily help avert (or try to avert) a war to get a peace prize...look at the case of last year. It is also not directly related to peace.

Read it on BBC. They have a decent coverage.