See, the economists believe we will have perpetual growth of something or other called wealth. If environmental impact is proportional to wealth or "gross product" or such in economic growth scenarios, the extinctions don't stop. Basically it goes on until it's down to us, our farm animals, our pets, and our pests.
But oh joy, we will be even wealthier than now in our further diminished world!
Whatever that means.
I think maybe it means everybody has a 600,000 square foot mansion with robot servants. We will be living on synthetic paste because the farmland will all be covered with big houses and big roads for our 98 ton cars. But what houses! What cars! We will all be the envy of our neighbors! We will all be members of exclusive clubs!
Maybe someday in the very distant future we will be rich enough to try to reconstruct our natural environment from whatever has been salvaged in arboretums and zoos! We will finally be able to afford the trees and flowers and birds and beasts that are now such an absurd and unconscionable extravagance, because they interfere with our accumulation of wealth.