Ask A Scientist

How many people are on the earth? What is the limit?

Asked by: Hezekiah Smith
School: West Middle School, Binghamton School District
Grade: 6
Teacher: Jo Ann Summerlee
Hobbies/Interests: Math, Biology, English Language Arts (ELA) & Humanities
Career Interest: Football and Basketball Player

Answer from Kyle Reeser

Biomedical Engineering Graduate Student, Binghamton University

Research Interest: Tissue Engineering and Neuroprosthetics
Interests/hobbies: Traveling, language studies, cooking and music

When my grandfather was born in 1922, there were approximately 1.9 billion people in the world. Today, my grandfather is 91 years old, and the population of our planet is estimated at 7.07 billion by the United States Census Bureau. Ten thousand years ago, toward the end of the last ice age, humans numbered only several million. It is enlightening, though, to consider the growth of humanity in the scope of how long it has taken for the population to double in the past.  It has been estimated that the number of humans was 500 million in 1500. For reference, the United States currently has roughly 316 million residents. In 1804, 304 years later, the earth's population reached 1 billion, and took 123 additional years to reach 2 billion in 1927. From that point, it would take only 47 years for another doubling of the population to take place. That occurred in 1974 when we hit 4 billion people.

According to the United States Census Bureau, the 7 billionth person was born somewhere in the world on March 21, 2012. This is of course a symbolic date as there is no way to know exactly how many people are on the earth at any given time. We are, however, projected to reach the 8 billion mark sometime in the mid-2020s. The relatively recent population explosion is due in part to the advancement of medicine and agricultural techniques. These resulted in a lower infact mortality rate, a higher average life expectancy, and the ability to increase crop yield with an exponentially increasing populace. Many scientists believe that Earth has a maximum carrying capacity of between 9 and 10 billion people. To calculate this rough number, we have to consider not only the space available for humas to live, but more importantly, the ability of the earth to produce food to sustain such a population. Farming in the 21st century requires fertilizers rich in nitrogen and phosphorus, as well as the dedication of millions of square miles of arable land. Crops and livestock also have an absolute requirement for clean, desalinated water. These are finite resources. In the United States, we have the privilege of going into a store and buying food, or turning on the tap and utilizing a seemingly endless supply of water. However, we trick ourselves into thinking that these resources are limitless Even today, over 780 million people lack access to clean drinking water. Of course, invention and innovation in the coming decades should allow humans to make better us of these precious resources, and could potentially increase the assessed carrying capacity of the earth by several billion people.

Last Updated: 9/18/13