The Quiet War by Paul McAuley
Twenty-third century Earth has been ravaged by climate change, and is now dominated by a few powerful families, with millions of people in prison and millions more labouring to rebuild ruined ecosystems.
Meanwhile on Jupiter and Saturn, live the Outers. They have built a wild variety of scientific utopias crammed with exuberant creations of the genetic arts. Now they want to colonise Earth and drive human evolution in a new direction.
On Earth, some want to launch a pre-emptive strike against the Outers while others wish to exploit the talents of the gene wizards.
It is clear that the fragile detente between the two branches of humanity is breaking down and they may be heading towards war . . .