The Last Exodus - Paul Tassi

The Earth lies in ruins in the aftermath of an extraterrestrial invasion, the land devastated by a desperate war with no winners between mankind and a race of vicious, intelligent creatures. The seas are drying up while the atmosphere corrodes and slowly cooks any life remaining on the now desolate rock. Food is scarce, trust even more so, and the only people left alive all have done horrific things to stay that way.