Effect of decreasing population growth-rate on deforestation and population sustainability

TL;DR

This paper analyzes how a declining human population growth rate impacts deforestation and sustainability, finding that for realistic parameters it does not significantly alter collapse probabilities, but for optimistic scenarios it greatly improves survival chances.

Contribution

It extends a human-forest interaction model to include decreasing growth rates, evaluating their effect on civilization survival probabilities.

Findings

Decreasing growth rate has limited impact for realistic carrying capacities.

Higher carrying capacities significantly increase survival likelihood.

Declining growth rates can raise collapse avoidance probability up to 95%.

Abstract

We consider the effect of non-constant parameters on the human-forest interaction logistic model coupled with human technological growth introduced in "Deforestation and world population sustainability: a quantitative analysis"[1]. In recent years in fact, a decrease in human population growth rate has emerged which can be measured to about 1.7% drop per year since 1960 value which coincides with latest UN projections for next decades up to year 2100 [2]. We therefore consider here the effect of decreasing human population growth-rate on the aforementioned model and we evaluate its effect on the probability of survival of human civilisation without going through a catastrophic collapse in population. We find that for realistic values of the human population carrying capacity of the earth (measured by parameter beta) this decrease would not affect previous results leading to a low probability of avoiding a catastrophic collapse. For larger more optimistic values of beta instead, a decrease in growth-rate would tilt the probability in favour of a positive outcome, i.e. from 10-20% up to even 95% likelihood of avoiding collapse.