First, this is how Edward Abbey expressed the same thought in a letter/interview with Karen Evans (18 June 1984):
I am a pessimist in the short run, by which I mean the next fifty or maybe a hundred years. In that brief interval it seems quite probable that too many of us humans, crawling over one another for living space and sustenance, will make the earth an extremely unpleasant planet on which to live. And this quite aside from the possibility of a nuclear war.This clarification shows that Abbey truly was an optimist: he assumed we would have surviving descendants.
In the long run, I am an optimist. Within a century, I believe and hope, there will be a drastic reduction in the human population (as has happened before), and that will make possible a free and open society for our surviving descendants, a return to a more intimate and tolerant relationship to the natural world, and an advance toward ... a civilized form of human society ... [elided for space].
I'm not so optimistic. I believe the damage we've done the world is nigh irreversible. Our "progress" goes forward unchecked. Most people in the industrialized world are too fond of their creature comforts. We prefer not to consider the consequences of our gas burning cars, or the coal that produces most of our electricity.
The damage to the ecosystem is global. People in Third World nations could possibly have survived if Industrial Society had spontaneously combusted in 1984; I'm not sure they have another fifty years to wait. Many scientists suggest that if pollution stopped today, it would take almost that long to reverse global warming.
This comes back to an off-hand comment I made over a year ago: humanity is a cancer on the face of the earth. What Abbey writes in another letter concerning cancer, seems a fit description of humans: "Delighting in nothing but multiplication, cancer ends by destroying both its host and itself."
Yes, I am feeling especially misanthropic and depressed this season. Why do you ask?