Populations

Several years ago, in “Half-Life,” I projected that the populations of other species, measured by the Living Planet Index (LPI), would reach the half-way point by this year (relative to its value in 1970). That isn't going to happen, mainly because humanity would need to be consuming 1.9 times the ecological production of the planet (“Earths”), and we are only consuming about 1.6.

This expectation is based on the notion, common in sustainability literature, that the sum of the ecological resources consumed by all species (including ours) is a constant. Further, it assumes that the consumption by other species are related to the size of its population as my current population-consumption model describes for humans. As I discussed in “Approaching the Peak,” our consumption appears to be climbing to a maximum of 2.0 Earths, which corresponds to an LPI of 0.46. I now project that if we manage to consume a little more than 3.1 Earths in a given year (a number very close to the constant pi), the LPI will be at zero, which is a euphemistic way of saying that we will have effectively killed the planet, and almost certainly ourselves. Note that this is another one of those strange rules of thumb: Consume up to one Earth to live sustainably; consume two Earths as a natural target (which may still coincide with consuming Nature's producers that we most depend on, and result in our population crashing), and consume three Earths to wipe out everything.

The U.N. recently reported its own projections for population and consumption in 2050. I was able to reproduce its numbers by performing curve fits on population and the consumption that I had derived in my recent modeling (see “Discontinuity”). As I did, they may have used three possible scenarios for population and consumption to derive their expected values. In my case, one of the scenarios is a “worst case” curve-fit, showing our population peaking in 2028 and dropping to zero by 2073; as our consumption falls, other species will have more to work with and their populations will rise after bottoming out at an LPI of 0.57. Another scenario is my population-consumption model's gradual leveling off as consumption stabilizes. The last scenario is a best-case curve fit, with our population and consumption rising rapidly, at the expense of other species, who die off by 2029. Combining these three scenarios using a PERT estimate is what yielded the U.N. estimates, which, if it meets the definition of “expected case,” will finish off other species by 2041, and likely us too.