Firewalkers

On a not-too-distant-future Earth, the global climate has been wrecked, leaving most of the landmasses parched and desolate. Most of the wealthy have fled up the space elevators to luxury ships they've built in the sky, leaving the rest of humanity to scrape for food and water, maintaining the solar power grids the best they can in order to provide a survivable environment.

The worldbuilding here is pretty interesting, but I found the teenaged characters and the story less than compelling. It's worth sticking it out, though, as the plot does come together nicely in the end. Fans of speculative climate fiction may enjoy this.