I agree totally that overpopulation is the root cause. My SWAG is that Earth can sustain 1 billion people, the approximate population in 1900. More than that, and we’re stealing resources from future generations. Now we’re at 6.5 billion and increasing rapidly, voraciously consuming Earth’s resources.

We have a choice now: we can either drastically limit greenhouse gases now to stave off devastation, while working towards reducing the population back to 1 billion over the next 100 years, or we can do nothing and let Earth do it for us by wiping out most of the warm-blooded animal and human life. The unknown is how long we can wait before making that choice.