Risks from increasing population sizes

By Chitra Maharani Saraswati et al | 5 March 2024
Frontiers

(Image by StockSnap from Pixabay)

The following has been extracted from a paper titled “Net benefit of smaller human populations to environmental integrity and individual health and wellbeing”. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Large human populations pose a risk of global catastrophe due to their influence on increasing environmental risks such as changes in atmosphere and climate, land degradation, and threats to biodiversity. Fundamentally, continued population growth leads to an increase in human economic activity, which puts pressure on the planet’s ability to renew resources. Population growth increases pressure and competition for finite resources such as food, water, and land; to compensate, production must rise, resulting in even greater environmental damage. With fewer people in the past, whenever environmental damage occurred, groups of people usually colonized other places or otherwise survived at lower densities. With today’s already large global population, the option to colonize new regions is unfeasible and instead drives additional environmental damage. The causes for these global environmental risks are not necessarily clear, so we consider the following main environmental problems arising from population growth: (i) greenhouse-gas emissions and temperature increases, (ii) pollution, (iii) loss of biodiversity, and (iv) spread of infectious diseases and general worsening health outcomes.

There is a strong theoretical basis for expecting a positive relationship between human population size and the risk of environmental erosion that are encapsulated by several mathematical concepts. Existing models built to quantify environmental impact arising from population pressures, such as the IPAT (Impact [emissions] = Population × Affluence × Technology), ImPACT (Impact = Population × Affluence × Consumption [intensity of use] × Efficiency [emissions per unit energy used]), and STIRPAT (a stochastic variant of IPAT), were developed mainly to determine the role of factors such as population growth and technological change in affecting environmental degradation. These equations and their variants can ideally predict the environmental outcomes of particular policy adjustments. For example, the ImPACT equation was constructed to assess total emissions as a function of population size, per capita gross domestic product, energy consumption per unit gross domestic product, and CO2 emissions per unit energy consumption. The following subsections reveal the extent to which the population component of impact equations cannot be neglected.

Greenhouse-gas emissions and climate disruption

It is axiomatic that an increasing population produces more emissions, but this simple relationship belies a complex interplay between consumption rate itself, and the total number of consumers. We explore this concept contextually before considering the consumption and production pathways resulting in different emissions profiles.

Increased concentrations of greenhouse gases generated from energy consumption, predominantly from burning fossil fuels, have contributed greatly to global environmental degradation. The Intergovernmental Panel on Climate Change (IPCC) Assessment Reports show that increasing emissions translate to additional global warming, reduced air quality, changes in the global water cycle, and increased prevalence of extreme climate events such as high rainfall and flooding, fires, droughts, and cyclones, with all the associated secondary adverse health impacts. Population growth has resulted in more human enterprise, and therefore, more intensive energy consumption. As new technology is developed, the energy consumption per capita also grows. Indeed, the annual per-capita rate of global primary energy consumption increased 1.62 times since 1965 to today (46.7–75.6 GJ person−1), or an average increase of 0.41 GJ person−1 year−1. During that same interval, the global human population increased from 3.3 to 8.0 billion and total annual greenhouse-gas emissions increased from 11.2 Gt to 33.0 Gt CO2-e.

A combination of more consumers and higher consumption rates drive the growth in greenhouse-gas emissions, rather than population growth alone. Nations with low per-capita emissions tend to have the highest population growth rates, meaning that if they follow the development trajectories of high-income nations today, emissions will also continue to grow. The latest IPCC report predicts a 1.7°C increase in global temperatures relative to pre-industrial temperatures (i.e., average of the 51-year period from 1850 to 1900) by 2060 under a scenario of low population growth versus 2.8°C warming with a medium-high scenario of population growth.

Consistently throughout history, there is a concomitant rise in per-capita energy consumption with population growth. As people gradually deplete resources in their environment, innovators find new ways to extract energy from previously unused resources or import resources from less-depleted locations. Increased energy use from these new resources facilitates improvements in diet and living standards, which stimulates even more population growth. This phenomenon is summarized succinctly by the concept of the ecological footprint, which describes how much biologically productive area is required to provide for all the competing demands of the people it services, such as space for agricultural and fiber production, timber, sequestration of carbon dioxide emitted from burning fossil fuels, and built infrastructure. This area can be calculated for the entire globe, or individual nations, leading to the estimate of biocapacity, which is the amount of biologically productive land and sea available to provide the resources a particular population consumes and to absorb its wastes (given current technology and management). Globally, we are operating on a biocapacity deficit that is consuming Earth’s ecosystems 1.7 times more rapidly than they can be renewed.

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