Warriors of the Rainbow

A man comes out of jail to find that Europe has been plunged into perpetual winter and that his girlfriend, having died in a mysterious epidemic, has been brought back to life as a test-bed for a laboratory-built brain.
He snatches the creature with his girl-friend's body and the government's billion-pound experimental brain from the research institute where she/it is being monitored by scientists and they live together happily - well, almost happily despite the disintegration of human civilisation all around them, till one morning the police break down their door.
The police don't actually know who they are, but their address has been supplied by the whales, who have ordered the governments of the world to put the couple on a small boat and send them out into the Atlantic.