Achieve Sustainability by Easing Population to 4 Billion by 2200

The past century of massive increases in human population and resource use has seen many undesirable environmental effects, ranging from biodiversity loss to climate change. But a research gap exists, as the ultimate causes are often not described with precision or mentioned at all. In this study, metrics of biodiversity, consumption, and pollution show extremely strong correlations when charted against human population size and its per capita impacts. We describe causal mechanisms for these correlations. Then, using available data, we show that slowing and gradually reversing population growth to ∼4 billion or less by 2200, while moderating per capita impacts, is the path toward sustainability. Among the benefits are habitat recovery and conservation of wild species, reduced greenhouse gas emissions and other pollutants, reduced conflict over resources, and the reduction of global poverty.