The quiet war / Paul McAuley.

Enhanced descriptions from Syndetics:

Twenty-third century Earth, ravaged by climate change, looks backwards to the holy ideal of a pre-industrial Eden. Political power has been grabbed by a few powerful families and their green saints. Millions of people are imprisoned in teeming cities; millions more labour on Pharaonic projects to rebuild ruined ecosystems. On the moons of Jupiter and Saturn, the Outers, descendants of refugees from Earth's repressive regimes, have constructed a wild variety of self-sufficient cities and settlements: scientific utopias crammed with exuberant creations of the genetic arts; the last outposts of every kind of democratic tradition.
The fragile detente between the Outer cities and the dynasties of Earth is threatened by the ambitions of the rising generation of Outers, who want to break free of their cosy, inward-looking pocket paradises, colonise the rest of the Solar System, and drive human evolution in a hundred new directions. On Earth, many demand pre-emptive action against the Outers before it's too late; others want to exploit the talents of their scientists and gene wizards. Amid campaigns for peace and reconciliation, political machinations, crude displays of military might, and espionage by cunningly wrought agents, the two branches of humanity edge towards war . . .