Philip Cafaro

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.

This simple, straightforward paper performs a useful service in comparing standard cohort-component projections of the global population with “system dynamics approaches." The latter place the human population in the economic and ecological framework...

Two approaches to assigning responsibility for global carbon emissions provide complementary insights. Individual-level analyses highlight the disproportionate emissions of the wealthy, and country-level ones highlight the growing importance of emissions from middle-income countries. We propose the concept of reasonable vs. excessive consumption as a way to integrate these approaches into a synergistic and less divisive perspective on how to address the current climate challenge. Commonly advocated efficiency improvements should be supplemented by cutting excessive consumption and acknowledging the role of population in sustainability goals in both high-income and poorer nations.

A dominant narrative in the climate change debate is that addressing population is not relevant for mitigation because population is only growing in the poorest countries, whose contribution to global carbon emissions is negligible, while the largest contribution comes from rich countries where the population no longer grows. We conducted an analysis of 30 years of emission data for all world countries showing that this narrative is misleading. Splitting the countries into four income groups according to the World Bank’s standard classification, we found that: (i) population is growing in all four groups; (ii) low-income countries’ contribution to emissions increase is indeed limited; (iii) the largest contribution to global carbon emissions comes from the upper-middle group; (iv) population growth is the main driver of emissions increase in all income groups except the upper-middle one; (v) the successful reduction in per capita emissions that occurred in high-income countries was nullified by the parallel increase in population in the same group. Our analysis suggests that climate change mitigation strategies should address population along with per capita consumption and technological innovation, in a comprehensive approach to the problem.