There are many potential solutions out there, so I don't want to make it seem like I'm the only person with an answer - but most of the efforts being made are at a government, corporate, or at least a technology infrastructure level. I think a more human-centric approach is more likely to be successful, because it enables people and communities to participate in fixing problems and repairing damage, but first I've got to figure out a way to get them to talk to each other without brandishing torches and pitchforks.

The short answer involves distributed networks of sustainably designed housing and food production, which can be scattered across what are presently sprawling empty deserts, and thereby decentralizing the population. Details to follow when I get things sorted out in a way that's presentable... With pictures!