I learned from Andrew Sullivan's blog about Volkswagen's initiative for motivating positive change through fun innovations. They've produced a few neat inventions and invite you to submit your own ideas for the chance to win an award.
I think that by adopting digital distribution, the gaming industry has already made progress in this field even though that was not the intent. Gamers want their fun; digital distribution gives them that fun more quickly and conveniently than retail and mail-order distribution. Game publishers and distributors, in turn, spend less on packaging and shipping. The benefits extend to the environment as an afterthought, but they are there.
One of Volkswagen's inventions is, in fact, a simple arcade game. I'm trying to think of other ways that games can be used to encourage environmental stewardship.