The thing we've been learning over the last 50 years is that catastrophic failure of one biome usually causes failure of other biomes. Even discounting feeding

The thing we've been learning over the last 50 years is that catastrophic failure of one biome usually causes failure of other biomes. Even discounting feeding 8 billion humans, just the maintenance required in keeping Spaceship Earth in a state (reliably) hospitable to humans is a surprisingly extensive task.