Though Blue Planet is set on another planet, it was created along an environmentalist theme, with a exhaustively researched and scientifically accurate setting. It is set 200 years from now, when the human race has irreparably damaged the ecology of the Earth. A myriad of plant and animal species have gone extinct, and a 75-year worldwide famine has just ended.
Many years before the fall of Earth civilization as it existed, a mysterious artificial wormhole was discovered beyond the edge of the solar system. Expeditions, and eventually a colonization mission were sent to the star system at the other end of the wormhole. The second planet of the system, dubbed Lambda Serpentis, was covered with a single vast ocean and was suitable for human life. This planet was named Poseidon.
After Earth was restored (other than ecologically), attempts were made to contact the colonists. In the interim, they had 'gone native', and the game explores the conflicts between the colonists, earth cultures, and the native cultures in a sort of Avatar on a water-covered world instead of a jungle-filled world.
It is a critically acclaimed setting, if not commercially popular. The game has gone through two versions (three if you include the obligatory GURPS conversion) and three publishers, and is now with Red Brick Publishing.
For more information, see the Red Brick site or the introduction by the original publishers.