by marko » Tue 08 Aug 2006, 16:10:58
If I may break into this conversation, the classic work on this question is William Catton's Overshoot. Catton points out that when an ecological equilibrium is disturbed (typically through a one-time increase in a nutrient) such that the population of a given species in a given area expands rapidly, the species always expands to the point that it not only uses up the added nutrient but degrades the environment needed to sustain it and thereby reduces that environment's carrying capacity. Consequently, the population decline is even greater than the population increase that led to overshoot.
In the case of human beings, overshoot has resulted not from a single nutrient, but from fossil fuels and particularly petroleum. This energy source not only increased the nutrient supply but also temporarily improved the human environment to sharply lower the death rate. However, the use of this energy source, and secondary consequences of that use, such as fertilizer runoff creating offshore "dead zones," has degraded the underlying environment of our planet. Overgrazing and erosion from overcultivation are destroying the soils that would have sustained us. Overfishing and pollution are destroying the oceans that would have sustained us. Fossil fuel use is disrupting the global climate in ways that will surely reduce crop yields worldwide and will probably cause a sea-level rise that will devastate key coastal environments and human habitats.
The consequence is that, even if Earth might have had a carrying capacity of 2-3 billion people in 1800, it can no longer support such a population without abundant fossil fuel. Even if the adjustment to the loss of petroleum and the depletion of fossil fuels were to proceed peacefully, the population would have to drop to something well below 2 billion and probably below 1 billion because of the damage to the planet. However, as MonteQuest points out, the adjustment is unlikely to proceed peacefully, and warfare is likely to kill even more people and further degrade environments.
In my opinion, the best-case likely long-term scenario for our species is a reduction to a population of several hundred million living carefully and sustainably in the parts of the planet that can still support human life. Hopefully, there will be some cluster of human population strong enough to preserve the existing elements of civilization, but with the added element of a profound respect for the balance of nature and an absolute prohibition against disturbing the environment on which our species depends.
The worst-case likely scenario is nuclear winter, which our species probably would not survive. Perhaps a small band of people would have the resources and foresight to build underground shelters on a remote South Pacific island, or a remote corner of New Zealand, and store enough food and fuel to get through the nuclear winter and its aftermath, as well as enough seeds to start over when the radioactivity drops off. Although in the very long run, perhaps it would be better for the biosphere if our species did not survive.
As I said before, my consciousness of likely doom makes me all the more appreciative of the joys and beauty that my life offers me in the here and now. Those are what keep me going.