Just look at decadence in rather inhospitable environments on earth... Let's take Dupai or some deserts in USA with golf courses. No way whole Earth will get worse than that. And basically we already have luxury lifes in such places, air conditioned malls, apartments, cars. Over use of water to water lawns...

Also, it is not like you couldn't vastly more cheaply and easily build Mars bunker on Earth. As we are centuries away from planet scale geo-engineering.