As I understand the term, saving the world means preserving it as a viable home to life, including human life. At the moment, the greatest threat to this goal is the continued uncontrolled growth of the human population. I personally doubt that even our present population is sustainable, since it is by now well known that, because of our impact on the earth, we are in a period of mass extinctions.
To sustain our six billion, so much biomass is being taken from the species around us that we are seriously attacking the diversity of the living community that makes the earth a viable home to life, including our own. Thus you have to see that maintaining and increasing our population of six billion is not at all equivalent to “saving the world.”
If the coming oil crisis results in a global famine and the death of billions (which is not unthinkable, though I personally am reluctant to make predictions about the future), then this would not work AGAINST saving the world, it would work FOR it. The period of mass extinctions would come to an immediate end. Civilization would be devastated, of course, but human life would not disappear.
The alternative of continued human growth to an anticipated twelve billion would, I feel sure, produce a much more dire future and a general and irreversible ecological collapse that would doom all or most large terrestrial organisms like mammals, including humans.
NOTE: At the present time (2019) human population has increased to more than seven billion.
updated: 27 Aug 2004