This article examines three contrasting approaches to an environmentally sustainable population via two criteria: normative desirability, and practical achievability within meaningful timescales for addressing the environmental crisis. Drawing on Strong Structuration Theory, we analyse the ‘ecocentric’, ‘equal shares’ and ‘pragmatist’ positions on sustainable population size. The ecocentric approach, advocating populations of 100 million to 2 billion based on notions of intrinsic value and biocentric equality, fails both criteria due to its contested philosophical foundations and inadequate conception of the relationship between values and action. The equal shares position, clustering around 3 billion living at equal welfare levels within planetary boundaries, demonstrates greater normative robustness by drawing from pluralistic frameworks like the Sustainable Development Goals, but remains practically unachievable within a meaningful timeframe due to demographic momentum and the political implausibility of required consumption sacrifices in wealthy nations. The pragmatist position, exemplified by Earth4All's ‘Giant Leap’ scenario, offers the most viable pathway forwards, by focusing on gradual transitions rather than absolute sustainability thresholds. This approach envisions global population peaking at 8.5 billion mid-century before declining to 6 billion by 2100. Our Strong Structurationist analysis reveals why rapid transformations in fertility preferences, consumption patterns or value orientations face structural constraints due to agents’ complex hierarchies of purposes and drive towards ontological security. The pragmatist position succeeds by working within existing motivational structures while gradually achieving sustainability goals, offering a potential pathway towards environmental restoration and human flourishing within timescales meaningful to current generations.
Samways et al. (Mon,) studied this question.