The global eco-system is self-regulating to a very great extent, or it would not have lasted billions of years. It's highly unlikely a runaway greenhouse effect will turn us into another Venus, the planet has survived continent-wide lava flows, colossal vulcanism, multiple meteoroid strikes, and constant plate tectonics. The result has been many climate changes, and even global ice-ages, but the sky has not fallen. There are too many feed-back mechanisms in effect for our puny meddling to destroy the planet.

Having said that, the earth is in a state of dynamic, not static equilibium, and if we continue messing with it it will change to a new mode, Le Chatelier's Principle, and adjust. It will not be the end of the world, or of life, or perhaps even of mankind, but it will be the end of post-industrial society as we know it. When Rome fell, people in the hinterlands still knew how to hitch up a plow to an ox and smelt metals, so the world did not slip back to the stone age. Today, very few people can start a fire without matches, or know how to tan leather, or make soap, or sew their own clothes, or any of the things which were common knowlege a century ago. In fact, most people, even athletes, can't walk across a mile of open country without shoes. When we fall we're going to fall back hard!

I remember at one Silicon Valley luncheon many years ago, my colleagues and I had this discussion. We decided to inventory our "19th century skills". "I can sail." , I said, "I know how to break and train horses.", said another, yet another could hunt with bow and arrow.

I asked my office partner what her 19th century skill was. "Golf", she replied, without missing a beat.