The Human Body Releases 2 Billion Tonnes of CO₂ Every Year Just by Staying Alive – But Is It Really Contributing to Global Warming?

Imagine billions of people breathing in and out every day. Every time we exhale, our bodies release carbon dioxide (CO₂) into the atmosphere. Now, scientists have discovered that the total amount of carbon dioxide produced by human bodies worldwide is surprisingly enormous: more than 2 billion metric tonnes every year.

A new study has revealed that human metabolism produces around 2.05 billion metric tonnes of CO₂ annually. Even more surprising, this amount has increased by 74% over the past three decades, mainly because the world's population has grown.

However, before worrying about the carbon dioxide released every time you breathe, there is an important distinction to understand. Unlike the emissions produced by cars, factories, and power plants, the CO₂ released by our bodies does not directly add new carbon to the atmosphere. Instead, it is part of the Earth's natural carbon cycle.

The discovery could nevertheless help scientists understand how carbon moves around the planet and improve the accuracy of climate predictions.

How Do Human Bodies Produce Carbon Dioxide?

The human body needs energy to perform almost everything, from walking and talking to thinking, sleeping, and maintaining a heartbeat.

We get this energy from the food we eat. During a process called cellular respiration, our cells break down nutrients, particularly glucose and fats, using oxygen to release energy.

Carbon dioxide is produced as a natural by-product of this process. It travels through the bloodstream to the lungs, where it is removed from the body when we breathe out.

This means every person continuously releases CO₂ simply by staying alive.

Although one person's daily contribution may appear relatively small, the combined output of billions of people becomes enormous.

According to the new research, human metabolism produces approximately 2.05 billion metric tonnes of carbon dioxide annually worldwide. This figure highlights how biological processes contribute to the movement of carbon through the Earth's environment.

Human CO₂ Production Has Increased by 74%

The study, led by Professor Javier Gonzalez from the University of Bath's Centre for Exercise, Nutrition and Metabolism, examined how much carbon dioxide humans produce through metabolism.

Published in The Lancet Planetary Health, the research estimated that global metabolic CO₂ production increased from approximately 1.18 billion metric tonnes in 1985 to 2.05 billion metric tonnes in 2015.

That represents an increase of around 74% in just 30 years.

But what caused such a dramatic rise?

The researchers found that the biggest reason was population growth. More people on Earth naturally means more bodies producing carbon dioxide through everyday biological activities.

In fact, more than 60% of the increase was attributed to the growing global population.

Changes in the amount of CO₂ produced by individual people played a much smaller role.

Professor Gonzalez explained that although everyone produces carbon dioxide by converting food into energy, scientists previously lacked a clear understanding of how much this process adds up to worldwide.

The research provides a more detailed picture of humanity's contribution to the global carbon cycle.

How Did Scientists Calculate CO₂ From Billions of People?

Estimating the total carbon dioxide produced by the world's population was not a simple task.

Researchers needed to understand how much CO₂ an individual produces under different conditions and then apply those measurements to the global population.

To achieve this, the team analyzed thousands of measurements collected from people across different stages of life, ranging from infants to older adults.

These measurements provided information about the amount of carbon dioxide generated by the human body during normal daily activities.

The researchers then combined this information with global population statistics and body-weight data.

By comparing these figures across different years, they estimated how humanity's total metabolic CO₂ production changed between 1985 and 2015.

The results revealed that the growing number of people was the main driving force behind the increase.

This approach allowed scientists to move beyond individual measurements and calculate the combined contribution of human metabolism on a global scale.

Why Human Breathing Is Different From Burning Fossil Fuels

One of the most important findings of this study is the difference between the carbon dioxide produced by human bodies and the emissions released by burning fossil fuels.

At first glance, both processes release CO₂ into the atmosphere. However, the source of their carbon is very different.

When humans breathe out, most of the carbon dioxide comes from food. Plants originally absorbed this carbon dioxide from the atmosphere through photosynthesis. Animals, including humans, then obtain that carbon by eating plants or other animals.

After the body processes this food, some of the carbon returns to the atmosphere as CO₂.

This process is part of the natural carbon cycle, in which carbon continuously moves between the atmosphere, plants, animals, oceans, and soil.

Fossil fuels work differently.

Coal, oil, and natural gas contain carbon that has remained underground for millions of years. When humans burn these fuels for electricity, transportation, heating, and industrial activities, that previously stored carbon is released into the atmosphere.

This adds extra carbon dioxide to the active carbon cycle and contributes to the increasing concentration of greenhouse gases responsible for global warming.

Therefore, the 2.05 billion tonnes of CO₂ produced through human metabolism cannot be treated in the same way as fossil fuel emissions.

Why Does This Discovery Matter for Climate Science?

If human breathing is part of the natural carbon cycle, why should scientists measure it at all?

The answer lies in understanding the complete movement of carbon around the planet.

Scientists use carbon budgets to estimate how much carbon enters the atmosphere, how much is absorbed by forests and oceans, and how much remains in the environment.

These calculations are essential for predicting future climate conditions and evaluating whether efforts to reduce greenhouse gas emissions are working.

Human metabolic CO₂ can also influence carbon measurements in densely populated areas.

For example, cities contain millions of people living, working, and travelling close together. The carbon dioxide released by their bodies becomes part of the local atmosphere.

If scientists do not properly account for this biological contribution, certain measurements could become more difficult to interpret.

By including human metabolism in carbon calculations, researchers can develop a more complete understanding of carbon movements and improve the accuracy of climate models.

The findings could also help scientists distinguish between carbon released through natural biological processes and carbon added through human activities such as fossil fuel combustion.

Does This Mean Human Breathing Is Causing Global Warming?

Despite the surprising numbers, scientists are clear that people should not misunderstand the findings.

The research does not suggest that breathing is a major driver of climate change.

It also does not mean people should reduce physical activity, eat less food, or change their lifestyles to lower the carbon dioxide produced by their bodies.

The central issue is the difference between recycled carbon and additional carbon released into the atmosphere.

Carbon dioxide from human metabolism largely comes from recently grown food and is part of the natural biological cycle. Fossil fuel emissions release carbon that was previously stored underground for millions of years.

This distinction is essential when scientists calculate humanity's impact on the climate.

Professor Gonzalez emphasized that the study is not claiming that breathing drives global warming. Instead, it provides a clearer estimate of how much CO₂ human bodies produce worldwide and how that amount changes as the population increases.

A New Piece of the Global Carbon Puzzle

The discovery reveals an unexpected fact about human biology: simply keeping billions of people alive produces an enormous quantity of carbon dioxide every year.

However, the real importance of this research is not that human breathing is causing climate change. It is that scientists now have a better estimate of another component of the global carbon cycle.

As the world's population continues to grow, understanding how carbon moves between living organisms, the atmosphere, land, and oceans will become increasingly important.

By improving these measurements, researchers can develop more accurate climate models and better evaluate strategies designed to reduce global emissions.

Ultimately, this study reminds us that not all carbon dioxide emissions are equal. Sometimes, understanding where carbon comes from is just as important as knowing how much is released.

Reference:

1. Javier T Gonzalez, Lorenzo Lolli, Bruno Spellanzon, Greg Atkinson, Ed Maunder, Alfonso Moreno-Cabañas, Jariya Buniam, Dylan Thompson, James Betts, Philip N Ainslie, Heliodoro Alemán-Mateo, Linda Bandini, Ellen E Blaak, Carlijn V C Bouten, Pascal Bovet, Soren Brage, Regina Casper, Prasangi Dabare, Barry W Fudge, Melanie Gillingham, Annalies H Goris, Michael Gurven, Hinke Haisma, Marije B Hoos, Noorjehan Joonas, Peter Katzmarzyk, Misaka Kimura, Sai Krupa Das, Pulani Lanerolle, Christel L Larsson, Marie Löf, Aviva Must, Marian Neuhouser, Theresa A Nicklas, Robert M Ojiambo, Kirsi H Pietilainen, Susan B Racette, Eric Ravussin, Leanne M Redman, John J Reilly, Susan Roberts, Luis B Sardinha, Analiza M Silva, Srishti Sinha, Anders M Sjödin, Eric Stice, Samuel S Urlacher, Edgar A Van Mil, Jeanine A Verbunt, Jonathan C K Wells, Tsukasa Yoshida, Xueying Zhang, Alexia Murphy-Alford, Cornelia U Loechl, Amy Luke, Michele Novaes Ravelli, Herman Pontzer, Jennifer Rood, Hiroyuki Sagayama, Dale A Schoeller, Klaas R Westerterp, William W Wong, Yosuke Yamada, John Speakman. Accounting for global carbon dioxide production from human metabolism between 1985 and 2015: a modelling study. The Lancet Planetary Health, 2026; 101546 DOI: 10.1016/j.lanplh.2026.101546