What would an ecologically-sustainable world be like? Like Ernest Callenbach's novel "Ecotopia" or different?

Question

The environmental movement is now mainstream. Smart Growth and New Urbanism is being practiced. Green Building and alternative energy are the rave. Mass transit is receiving high ridership. Ernest Callenbach's novel "Ecotopia" is still popular. Religion is embracing the environment. What will an ecologically-sustainable society be like? And could Northern California, Oregon, and Washington actually seceded to form a sustainable society?

Answer 1

The best way to achieve an ecologically-sustainable world is to reduce the population to around 2 billion people. Which of the remaining 5 billion people are you going to 'eliminate' and how are you going to do it?