What is needed is a world government; something approximating to a benevolent dictatorship. Prerequisites (or at least, expedients) to this include declines in organized religion and in population.
One could reply (correctly) that the world politic is populated by (more or less) corrupt governments, and that a world government is therefore untenable, at least in the political short-term of even a few hundred years, by which time the species may well be dead or greatly reduced. One could further argue that several self-interested nations make for a better balance of power, or political ecosystem, than does a realized world-government. The reply to this involves at least two points: 1. The earth for all practical purposes is finite, and 2. as I hinted before, I'm not thinking in terms of a few hundred years (although that would be nice). I'm thinking of an end goal which ought eventually to be realized.
True, we're far more likely to nuke ourselves or have a massive die-off via some other means prior to the establishment of such a system, but I say it's worth keeping in mind. This is why another of our great imperatives as a species is to get off Earth, but everybody already knew that.