The nobel peace prize is supposed to be given for promoting peace, not doing good deeds for others. Heroism has nothing to do with it.
The requirement is: "...shall have done the most or the best work for fraternity between nations, for the abolition or reduction of standing armies and for the holding and promotion of peace congresses".
Even bad people can get it, provided that they do something to promote peace.
Al Gore wasn't given the prize alone, he shared it with an organization.