Although Martin Rees beat me to the comment by hours, I agree with him to a point. He believes there is no better than a 50% probability that homo sapiens will survive the 21st century. Since he is one of the premier scientists in the world, his opinion, unlike mine, cannot simply be laughed off.
It is my belief that we as a race do not care to believe that a warming trend exacerbated by the human race; religious wars; emerging biohazards; the end of cheap energy, a dwindling food supply and many people’s irrational belief that some invisible God will protect them (although that idea is contrary to Scripture if one believes Scripture), have brought the planet to a condition of overpopulation which no one is willing to control sufficiently to stop the population explosion, the proximate cause of EVERY problem the world now faces. The point is, the trend is not reversible.
Since it is not politically correct to suggest that everyone does not have the absolute right to pump babies out at a rate which will destroy the earth within the next two hundred years, or at least exterminate 90% of the indigenous life on land and in the seas thus generating an immense die-off, I feel absolutely safe in predicting a mass extinction event before the end of the 22nd. century, WITHOUT the need to resort to nuclear exchanges.
While this is not a doomsday scenario, it could become one in an instant with the collision of an earth-crossing body (one much smaller than the K/T impactor would do); the eruption of a supervolcano; a surprise release of a few trillion tons of Carbon Dioxide marginally bound in ice on the ocean floors; or the main short-term problem: The actions of humans, evolved to live as hunter-gatherers, trapped in huge societal groups. An anger is building. People want to separate, but they cannot in many cases. This will not work itself out in behavioral modification patterns. People will start killing each other. As has been said by one smarter than I, no country is more than three meals from a revolution.
For years I have been considering the man-machine interface because I understand that we have to escape this physical form and get out into the galaxy in order to survive as an intelligence. I had always contented myself with the thought that science could overcome these problems, likely within the next few hundred to a thousand years, well before our sun cooked us. But now I realize that there have been several mass-extinction events in our geologic history and we are overdue. The question is, will enough people remain to pick up the pieces, re-learn the current knowledge and advance it fast enough to meet the new deadline of one billion years. It is actually closer (we guess) to 1,100 million years, but there are going to be at least three more mass extinctions during that period, assuming the earth is inhabited at all.
Let me give you some news. The world was not created by God less than 6,000 years ago. There are several reasons for this, but the most compelling is that God simply doesn’t exist. Jesus probably did exist, but he was as looney as David Koresh and when he died, that was it. He is dead and is NOT coming back. I won’t even argue it. If you don’t believe me, learn Greek and study Flavius Josephus. But it is highly improbable that we will finish the 22nd. century without a mass extinction event or a nuclear holocaust between zealots who want to kill each other over who has the best invisible pal in the sky.