I just empirically derived the logistic function for world population growth. As I described in the post “Discontinuity, ” humanity has been able to approach the maximum limit to consumption of ecological resources by radically increasing what I call the “extraction mass,” and the new analysis shows that our population growth is adapting just as populations of other species do when faced with similar constraints: by reducing population growth through competition.
Our consumption is converging toward a value that is twice the amount of renewable resources that the natural world produces (its “biocapacity”). Since 1980, we have been consuming both biocapacity and “natural capital” -- the parts of the biosphere which generate that biocapacity. Natural capital recycles as well, by an amount that appears to be equal to biocapacity, accounting for the other “Earth.” This is the ultimate power of our technology: to destroy our planet's mechanisms for sustaining life. If we ever reached that limit, we would either need a totally artificial life support system (for us) or our population would crash, perhaps never to recover.
My analysis indicates that the maximum population is 8.69 billion people, based on the current value of extraction mass (which, together with the apparently constant “transaction mass,” determines consumption). World population is currently about 7 billion, and is projected to be within 10% of the peak by 2023. For contrast, in 1980, when we were consuming just all of the biocapacity, the population was 4.53 billion; this is how many people a healthy world could support at our current average lifestyle (represented by extraction mass).
Ironically, if we hadn't increased extraction mass right after World War Two, from an equivalent ecological footprint of 0.018 hectare to 2.5 hectares, the maximum population (for consuming two Earths) would have been 29.09 billion people, and for consuming one Earth it would have been 20.48 billion people. More people could have lived, but they would have had a lower life expectancy (at the peak: 55 years for one Earth and 58 years for two Earths) and happiness (42% for one Earth and 47% for two Earths, again at the peak). At our present population, the average world consumption would have been 8% of its current value, life expectancy would have been 45 years, and happiness would have been 30%.
Evidence continues to accumulate that biocapacity has been degraded by our consumption of natural capital – effectively overwhelming the natural world. Not the least of this evidence is related to global warming, which at this point may be unstoppable. The most obvious consequence is a reduction in the maximum population, and I'm afraid that the only real control we have is with the variable that pushed us so close to disaster: our lifestyle. It may be inevitable that mortality will increase, and it will come from either growing competition as we approach peak population, or less time for each of us to make an impact as we let the natural world have more influence over our lives.