Most of the time, you don't want to save the world because this presents scaling problems. Instead, save a little corner of the world and be open about how you are doing it. If you do this right, then you will garner lots of imitators. Then if your way of "saving the world" is well documented and robust enough to avoid the "cargo cult" pitfall, you will convince some large part of the world to save itself.

Note the implication: You don't save the world by telling it, "You're doing it wrong." You save the world by getting the world to covet your success.