Carrying Capacity

How many pets do you have? Too many? Not enough? How many do you think you would be able to have and sustainably keep up with feeding, making sure they have enough space in your home, walking, cleaning up after them, and everything else it takes to keep your pets and your home happy and healthy? Perhaps you have technology such as a robot vacuum that will help you keep up with dog hair all over the place. Maybe you just got a higher-paid job and can access more resources for your pets.

This is a minor example of carrying capacity, which is the measure of how much an environment, in this case your home, is able to sustain. With your robot vacuum and your new job, you increased your home's carrying capacity.

In this explanation, we will see how carrying capacity relates to us on a global scale.

Carrying Capacity Definition

Carrying capacity is often used in ecology and biology, but in this explanation we consider it in relation to demography and human geography.

Carrying Capacity in Human Geography

In human geography, carrying capacity refers to the number of people a place such as a town, city, country, or the world can support. We live on a planet with exponential human population growth and finite resources. This leads many to estimate what would be the number of people that the planet can support. Earth's human population has rapidly increased over the last couple hundred years, from one billion in 1804 to eight billion in 2022.¹

We can't move to another planet, so concerns over how the human population can grow sustainably on Earth are at the heart of much current debate. Resources, such as fossil fuels, are finite, and indeed, are decreasing in quantity. There are also limits to renewable resources such as water, air, soil, and forests, so how can we stop from exceeding the Earth's carrying capacity?

Fig. 1 - Human population growth

Models of Carrying Capacity

There are different ways a population can relate to the carrying capacity of an environment:

R-selected vs. K-selected Species

R-selected ("R") species emphasize quantity over quality, whereas K species invest effort into few offspring.

K species typically require more concentrated effort and resources per individual, whereas R species have a lot of offspring to increase the chances that some of them will thrive.

Humans are a K species. However, over the last few centuries, humans have experienced explosions in population growth typically seen in an R species.

This is where humans face a predicament. How can we cope with growth like an R species while requiring the resources and consumption of a K species on a planet with finite resources?

Exponential Growth

Populations undergoing exponential growth experience rapid expansion. They exceed the carrying capacity of an area for a time before being brought back below the carrying capacity due to exhaustion of resources and competition. This type of growth becomes unstable. Going above capacity degrades the environment and starts to lower the environment's carrying capacity leading to a downwards spiral if the pattern continues. This ebb and flow is natural for populations that experience exponential growth. Exponential growth has been seen in the human population since the Industrial Revolution.

Fig. 2 - Exponential population growth

Often organisms with access to abundant environmental resources experience exponential population growth. Resources are abundant until the carrying capacity is exceeded and resources become scarce. Humans have experienced abundance as our ability to use tools and ingenuity led to advances in technology that have allowed us to cultivate and make use of natural resources, unlike other species. These advancements, such as agriculture and industrialization, were followed by huge increases in the human population.

Logistic Growth

Logistic growth is a slow and steady increase in growth that levels out at a sustained carrying capacity. This model provides a sustainable population to live in an environment with finite resources because the population is at the maximum level not to degrade the environment. The rate of growth will get smaller and smaller as the population nears the carrying capacity.

Fig. 3 - Logistic population growth

These models show a desirable model of sustainability. But remember, human and technological advancement can increase the carrying capacity of a place, expanding economies of scale and using natural resources in a more efficient and effective way that makes exponential growth a more realistic model of sustainability.

However, advances in technology that continue the exponential growth trend that humans are on means we will be increasingly dependent on advancing technology to produce more food, use less waste, and tap into new resources to raise the carrying capacity and at the same time prevent the degradation of environments that would lead to population collapse. This increases dependency on human-created systems.

Carrying Capacity Example

A famous example of carrying capacity is Ireland during the potato famine of 1845 to 1849.

Another example is the collapse of ancient Maya city-states like Tikal and Copan.

Carrying Capacity of the Earth

The Earth's limits to sustain us vary depending on what source you read, particularly because, as we pointed out above, technology can increase carrying capacity.

The number of people the Earth can support is largely unknown. Estimates have put the number from far below the global population of today to over a trillion people.⁸ If the carrying capacity is actually below today's population, then it can be assumed we are degrading our environment in an unsustainable way.

Models for predicting Earth's carrying capacity such as the Stockholm Resiliency framework focus on environmental changes that may inhibit population growth, such as climate change, ozone depletion, and freshwater usage.¹⁰ The prevalence of these change factors can be measured, although it is difficult to predict with certainty what may happen when their limits are exceeded. Nevertheless, they can be monitored as causes of instability and indicators that the population has reached a limit on carrying capacity as the Earth is no longer keeping up with the stresses being put on it.

Looking back, for thousands of years, human ingenuity has been increasing the carrying capacity of our environment. Because large amounts of food could be cultivated in a relatively small space meant that people could do things besides hunt and gather, thus creating the first economies of scale. It is estimated that the human population of the Earth would be a fraction of its current size if we were still hunter-gatherers. The environmental limitations of fertile natural land on Earth that could support a hunter-gather society would be the carrying capacity for humans.¹¹

Importance of Carrying Capacity

Sustainability often seems to conflict with economic development and growth. Many already question if there are enough resources on the planet to support the current population. Many experts ask how exponential economic growth can be maintained with finite resources? However, modern technological advances already show signs of easing the need for physical resources. Computers and the Internet ease reliance on paper, for instance. Other communication technologies lessen the need to travel and use fossil fuels, or physical resources to communicate with one another.

Alternative energy technologies can diminish the need for fossil fuels. Many energy companies are starting to adapt, but some showcase sustainable policies while not adopting them on a large scale. This is often equated with something known as greenwashing: when you want to look, act, and talk like you are environmentally sustainable and eco-friendly, but in reality you are not. Who would do that?

Sometimes the technology is just not there (yet), or else it can be a question of political will, or, more often than not, projected economic losses that would panic shareholders.

Is a major global population or resource crisis inevitable? Would this be a catalyst for sustainable change? These are fundamental questions for the 21st century.