Population is about far more than numbers, however. It’s also about ages, abilities, lifestyles, and consumption. One approach scientists are increasingly using to study population is through the concept of "ecological footprint" pioneered by Mathis Wackernagel and William Reese. The footprint model calculates the area of the Earth’s productive surface (land and sea) necessary to support a particular lifestyle or level of consumption

Viewed that way, every person has a "footprint" that falls on the environment. At the most basic level, it includes enough land to produce food and fiber – to raise crops and graze animals and grow trees – and enough clean water to drink, wash and irrigate. We also need enough land to supply some sort of energy for heating and cooking, and to safely dispose of the wastes we generate.

As individuals’ lifestyles and consumption expand, so do their footprints. As nations become more industrialized and their standards of living increase, they consume more resources, and occupy a larger footprint. They need more farmland to support higher protein diets, and may clear forests, plow prairies, or fill wetlands to provide it. They need more water, and have to tap more lakes and aquifers, and dam and divert more rivers. They need more energy, and have to build more power plants, burn more fuels, and release more pollutants.

Growing populations and higher levels of development also require additional infrastructure and increased levels of social and community services. More people need more housing, hospitals, roads, schools, parks and playgrounds. More highly developed societies, because their consumption is greater, use more land and resources per person. To support their economies and produce consumer goods, they require more factories, offices, businesses, and shopping centers. To dispose of their wastes, they need more landfills, sewage systems, and toxic containment sites.

Each of these needs is met by extracting resources from the environment, often without replenishing them. The more people on the planet – and the greater the average level of consumption by any individual or group – the more resources are required to meet those needs and the larger the human footprint on the planet. The larger the human footprint, the less area remains for other species and natural systems.

Carrying Capacity and Population

The total human footprint the Earth can withstand is expressed as the "carrying capacity" of the planet. Carrying capacity is the maximum number of people the Earth can support without endangering its ability to support that population in the future. A population that does not erode the resource base or otherwise degrade the planet’s ability to support that population in the future is considered "sustainable".

Carrying capacity is difficult to accurately assess, however. In recent years, the Earth’s carrying capacity has been suggested to be as low as one billion people, or as high as 40 billion people. Environmentalists and biologists typically put forth lower numbers, while economists and businesspeople often put forth higher figures.

This divergence appears to be rooted in philosophy. Many growth advocates argue that increasing population is necessary to provide more workers and consumers to expand the global economy. And they suggest that the natural ingenuity of people will overcome the problems this growth creates.

Some industrialized nations, such as Germany, with stable populations already face shortages of younger workers, and growth advocates argue that their economies will suffer as populations age. Not only may there not be enough workers to keep up production, they suggest, but there may not be enough workers to pay into retirement and medical plans to support older citizens.

Advocates of "sustainability" argue that increasing population and consumption are already causing damage to the planet, and that deforestation, soil erosion, extinction of species, and pollution of air and water are all indicators of exceeding carrying capacity.

Population Connections

One way to view the issues and impacts of population growth is through the "Global Issues Mobile". Essentially it shows that as our population increases, human needs – food, water, energy, livelihood, etc. – increase as well. We attempt to meet those needs by consuming more resources.

When population levels reach a critical threshold, we then see both a decline in the resource base, and damage to the environment, which supplies all those resources. These trends reinforce each other – the damaged environment provides fewer resources, and the shortage of resources causes us to further damage the environment. At some point, when there are not enough resources to go around, we see significant scarcity, and poverty, which is the human face of severe scarcity.

Scarcity and poverty underlie a number of problems. One is discrimination. When resources are scarce, those in power often decide who won’t get a fair share, and may discriminate against women and girls, or other races, religions, or economic classes.

When resources are scarce, people may also move in search of more resources. There are hundreds of millions of migrants in the world today, seeking food, water, land, and work. Scarcity drives legal and illegal immigration into the US and other industrialized nations as people struggle to survive and support their families.

And when scarcity is acute, people may engage in conflict over resources. As world population and consumption grow, environmental impacts multiply, and resource scarcity worsens. As environmental destruction and scarcity spread, and as more people compete for limited resources, social, ethnic, and political tensions increase. This combination drives political instability, declining social health, and greater migration.

The combination of population, consumption, and scarcity has fueled more than 150 armed conflicts since the end of World War II, and driven tens of millions of people from their homes as economic migrants or refugees. As shortages of essential resources such as water, farmland, and fisheries reach critical levels, many security analysts expect conflict over those resources to intensify.

Ultimately, our own numbers, and the lifestyles many of us choose to live, drive all the critical issues we confront. Left unchecked, the combination of population growth and consumption – along with increasing inequity between rich and poor individuals and nations – will ultimately threaten not only the well-being, but also the lives of a majority of people on this planet.

1 | 2 | 3

next in depth issue