I hugely recommend Alien Earth, by Megan Lindholm, who is better known as Robin Hobb.
Genuinely my favourite scifi book, and her only scifi novel. SUCH an interesting take on climate fiction and dystopia.
Aliens came to 'save' us from our own wanton destruction of the planet, but we end up as unwitting, infantilised slaves to them, along with the living ships we use to cross the stars.
A human from the original evacuation had cancer and should have been purged, but>