Earth’s Carrying Capacity Has Increased Over Time: Here’s How

Earth’s carrying capacity, the number of humans our planet can support, has been long debated and there is no clear answer. Every species has a carrying capacity – an environmental limitation on the size of a population given the availability and use of resources like food, water and materials. Humans have the ability to manipulate the Earth’s carrying capacity like no other species; to develop technology, exploit the environment, and create medicines and tools that allow for longer, healthier lives and increase our planet’s ability to sustain human life.

7 Events that Drastically Increased Earth’s Carrying Capacity

While many events have enabled Earth to support more people, the following seven have had a significant impact due to their large scale and longevity.

1. The Neolithic Revolution (10,000 BC)

During this time, early humans transitioned from nomadic hunter gatherers to settled agrarian-based societies, modifying their environment with irrigation, deforestation, domestication of plants and animals, and the use of tools. This allowed for a surplus of food and the ability to support larger populations. The Neolithic Revolution is considered the first revolution in agriculture.

2. Four-crop rotation (mid-1700’s)

Charles “Turnip” Townsend introduced a new type of crop rotation – rotating crops every four years and including wheat, barley, turnips and clover. Grain yields drastically increased, soil fertility improved, and livestock began grazing directly on the clover and turnip crops which increased their health and productivity.

Schematic of Alexander Cumming's 1775 patent for the S-trap

3. Modern design of the flush toilet (1775)

The ability to properly dispose of human waste has immense impacts on human health, as it prevents bacteria, viruses, and parasites from contaminating water, soil and food. Because deadly diarrheal diseases have a disproportionate impact on children, improvements in sanitation significantly reduce infant mortality rates.

4. Vaccines (1796)

In 1796 physician Edward Jenner discovered a safe vaccine for smallpox which had previously killed 400,000 people annually in Europe. Immunization rates have skyrocketed in the years since, protecting people from a range of serious, and sometime life-threatening diseases including diphtheria, hepatitis B, measles, polio, and rubella. The World Health Organization estimates that vaccines prevent two-three million deaths annually.

5. Steam engine

Steam locomotiveThe steam engine was developed and perfected over time, opening the door to many of the advancements that took place during the Industrial Revolution. Use of the steam engine during the Industrial Revolution allowed food to be transported quickly over long distances which drastically improved nutrition, resulted in large factories and the more efficient creation of goods, and enabled more rapid excavating of mines to support an ever-growing number of people on Earth.

6. Chemical Fertilizers (1913)

The first factory to produce synthetic ammonia, the main ingredient in chemical fertilizer, ushered in the era of modern agriculture. The development of fertilizers had big implications for food production, allowing crop yields to increase on smaller and smaller land. In fact, it’s estimated that fertilizer has enabled the lives of several billion people who otherwise would have died prematurely or have never been born at all. Today fertilizers account for 50% of the world’s food production.

7. Antibiotics (1940)

Penicillin, discovered in 1928, was developed into an antibiotic in 1940, transforming medicine worldwide. Before penicillin was discovered, the three leading causes of death were pneumonia, tuberculosis, and diarrhea, which (together with diphtheria) caused one third of all deaths. Antibiotics were hailed as a miracle drug and are now prescribed at least 150 million times every year.

Unintended Consequences

While all of these events increased global carrying capacity by enabling longer and healthier lives, they did not all have equitable impact around the world. For instance, according to WHO, there are still over 2.3 billion people in the world who do not have basic sanitation services (toilets or latrines). Coming in at 85% coverage, vaccinations are also not universal and WHO estimates that 1.5 million deaths could be prevented if vaccination rates improve.

Additionally, many of the technical and medical advances that temporarily increase carrying capacity can have unintended consequences over time. Introduction of the coal powered steam engine, for example, marked the beginnings of climate change and extensive use of antibiotics has created resistant strains of bacteria that lead to outbreaks and create a risk to public health.

For a deeper look at advances that have increased the Earth’s carrying capacity through history, check out the activity, Peopling of Our Planet.

Photo credits: S-trap schematic:, Steam locomotive: Sci Planet