If current trends continue, we may have 13 years before the world’s population reaches a maximum of 7.1 billion people and then declines rapidly. This is due to an apparent correlation between consumption and population size: As ecological footprint increases, population peaks and then decreases. We can stretch the time until the population peaks by decreasing our consumption exponentially by two percent for 20 years; four percent for 30 years; five percent for 50 years; or six percent for 60 years (the latter resulting in 130 years to the population peak but a very low life expectancy of 31).
The amount of oil reserves remaining when the population peaks under business-as-usual conditions will be 33 years at the current production rate (it is presently 40 years). For each of the cases where we limit consumption the amount remaining at the end of the period will be 23-25 years of consumption at the current rate. These numbers imply that resource scarcity alone is not likely to be responsible for the decrease in population after the peak.
For my sample of countries, life expectancy seems to peak at about 75 years, corresponding to a peak in ecological footprint, marking what appears to be a condition of unstable equilibrium. Ideality, the average of life expectancy and happiness, likewise reaches a maximum of less than 80 and gradually decreases as happiness continues to increase. Could it be that there is a natural limit to humans, rather than our environments, that keeps us from living an ideal existence?