2 Billion Tons of CO₂ from Human Breathing Annually—Why "Breathing is Bad" Isn't the Right Conclusion

Walking to the station. Eating lunch. Working. Sleeping at night. Our bodies continuously use energy without rest.

This life activity produces carbon dioxide (CO₂). What would be the total amount if we summed up the CO₂ produced by each individual's body worldwide?

Research led by the University of Bath estimated this amount to be 2.05 billion tons annually as of 2015. This represents a 74% increase from 1.18 billion tons in 1985 over 30 years.

It's a staggering figure. However, interpreting this news as "humans are polluting the Earth just by breathing" misses the important aspects of the research.

The focus is not on blaming human existence as a source of emissions. It's about capturing the movement of carbon between food, the body, and the atmosphere more precisely than before.

When is the "2.05 Billion Tons Annually" Figure From?

First, it's important to note the difference between the time of the research's publication and the period the figure represents.

The research was published in 2026, but the figure of 2.05 billion tons is an estimate for 2015. It is not a direct measurement of the breathing of the world's population in 2026.

The study focused on changes from 1985 to 2015. The amount of CO₂ generated by human metabolism increased by approximately 870 million tons annually during this period.

Moreover, the metabolism discussed here is not limited to what occurs during exercise. It also includes the process of using nutrients from food to maintain body temperature, keep the heart beating, and sustain various bodily functions.

In other words, this research aimed to capture the flow of carbon associated with human life activities, not just specific actions in daily life.

How Was the Breathing of People Worldwide Estimated?

Of course, the research team did not attach measuring devices to all of humanity.

The researchers utilized measurement data on the metabolism of people living their daily lives. According to the researchers' public explanation, they combined measurements from 6,756 people using the "doubly labeled water method" with data on the world's population and body weight.

The doubly labeled water method uses stable isotopes of hydrogen and oxygen as markers to track movements within the body. By utilizing the differences in the rate of loss from the body, it is possible to estimate CO₂ production and energy consumption.

The advantage of this method is that it allows for the investigation of energy consumption in daily life. It connects people's lives and metabolism in a way different from short-term measurements in a laboratory.

This research draws a comprehensive picture by linking such individual measurements to global population information.

However, even though based on actual measurement data, the global value is an estimate from a model. It is not the result of directly measuring residents of all regions under the same conditions. This distinction is important when considering the precision of the figures.

The Main Reason for the 74% Increase is "Population Growth"

Hearing that CO₂ increased by about 74% over 30 years might lead one to think that each individual's body now consumes much more energy than before.

However, the central factor indicated by the research was population growth. More than 60% of the increase is attributed to the growth of the world's population.

The "more than 60%" here does not mean 60% of the total CO₂ amount. It refers to the proportion of the increase from 1985 to 2015 that can be explained by population growth.

According to the researchers, weight gain also contributed, but its impact was smaller than that of population growth.

It is not appropriate to connect this result to assigning environmental responsibility to people of certain body sizes. The research deals with the carbon flow of the entire group, not judging individual lifestyles or values.

When reading the global total, it is important to separate "changes per person" from "changes in the number of people." This basic principle is crucial in this case as well.

Why is CO₂ from Breathing Different from Fossil Fuels?

CO₂ from breathing and CO₂ from burning oil and coal are the same molecules. Being derived from breathing does not change its special properties.

The difference lies in where the carbon contained within comes from.

We take in carbon through food. This carbon, if traced through the food chain, mainly connects to what plants have relatively recently absorbed from the atmosphere through photosynthesis.

Plants absorb it, it becomes food, passes through the human body, and returns to the atmosphere. Breathing is part of this relatively short carbon cycle.

On the other hand, burning fossil fuels releases carbon that has been stored underground for an extremely long time into the atmosphere.

Therefore, it is not possible to simply align both emissions and assign the same contribution or responsibility to global warming.

When considering breathing, it is necessary to also include the absorption by plants in the preceding stages. Counting only the exit without considering the entrance can lead to misreading the carbon balance.

"The Amount of Carbon Moving" and "The Amount Increasing in the Atmosphere" Are Different Matters

The key to understanding this research is distinguishing between "a large amount of CO₂ being produced" and "that amount leading to a net increase in atmospheric CO₂."

For example, consider a tank where water flows in and out simultaneously. Looking only at the amount that flowed out from the exit doesn't tell you how much the water level in the tank has risen. Both the inflow from the entrance and the outflow from the exit are necessary.

A similar perspective is required for carbon.

The large amount of carbon moving through the human body is important in describing the cycle. However, it does not mean that a new factor contributing to global warming of 2.05 billion tons has been found.

The researchers aim to depict more precisely where carbon moves from and to. Especially in cities where populations are concentrated, CO₂ from human metabolism becomes one element in understanding regional carbon movements.

"Identifying as a source" and "treating as a target for reduction" are not the same.

What Is Being Discussed on Social Media? Points Emphasized by Researchers

Regarding this research, the publicly confirmed social media posts include a LinkedIn post by Professor Javier Gonzalez, who led the research, and a shared post by the University of Bath's research center.

Professor Gonzalez introduced the research results and explained that CO₂ from metabolism is biologically derived, circulating carbon recently absorbed through photosynthesis. He clarified the difference from adding fossil fuel carbon to the atmosphere on social media.

The research center also posed the question of how human metabolism relates to global CO₂ production and introduced the paper.

However, these are communications from researchers and research institutions and do not represent the approval or disapproval of the general readership. The publicly available information did not sufficiently capture posts from general users directly reacting to this research.

Therefore, it is not possible to introduce reactions such as "a flood of criticism on social media" or "concerns about taxing breathing" as verified facts.

What can be gleaned from the confirmed communications is that the researchers are trying to convey not only the magnitude of the numbers but also the "origin of the carbon." This explanation is an important part that can easily be overlooked in just the headlines.

Three Misinterpretations Japanese Readers Should Be Aware Of

In Japan, if only the "20 billion tons annually" part of this news is extracted, the meaning can change significantly.

The first misinterpretation is that "reducing breathing is good for the environment."

The research team did not state that breathing is a problem. They did not recommend refraining from exercise or changing diets based on the research. Measuring life activities and proposing behavioral restrictions are separate matters.

The second misinterpretation is that "since the world's population has increased, climate change is just a matter of numbers."

The estimate was for CO₂ from human metabolism, not the emissions of society as a whole, including transportation, power generation, and industry. It is not possible to narrow down the causes of climate change to one factor beyond the research subject.

The third misinterpretation is that "if breathing is part of the cycle, then all emissions related to diet don't need to be considered."

Metabolizing food within the body and the processes of producing, processing, and transporting food involve different processes. The explanation of carbon from breathing alone cannot conclude the environmental impact of the entire system of delivering food.

What is important is to consider what the measured numbers represent and what can be inferred from those numbers, one by one.

After "How Much Was Emitted," Ask "Where Did It Come From"

The estimate of 2.05 billion tons visibly demonstrates that the human body is part of the Earth's material cycle.

The food on our tables fuels our bodies, and some of its carbon returns to the atmosphere through breathing. Our daily activities are not disconnected from plants, soil, or air.

Therefore, the interest of this research does not lie in the narrative of "even breathing has become villainous." It lies in reinterpreting life activities, which are too familiar to be conscious of, as part of the global carbon flow.

When reading news about CO₂, after focusing on the magnitude of the quantity, it's worth adding another question.

Where did that carbon come from, and where does it return to?

Only by looking this far can we understand what the enormous numbers mean.

Sources and References

1. Phys.org: Overview of the research, estimates from 1985 to 2015, contribution of population growth, and differences between breathing and fossil fuels.
   https://phys.org/news/2026-10-human-metabolism-billion-metric-tons.html

2. University of Bath: Official announcement by the research institution. Used to confirm the meaning of the figures, the purpose of the research, and the explanation that the study does not call for reducing breathing or exercise.
   https://www.bath.ac.uk/announcements/human-metabolism-produces-two-billion-tonnes-of-co2-a-year-global-study-finds/bath.ac.uk

3. The Lancet Planetary Health: Original paper. The paper is titled "Accounting for global carbon dioxide production from human metabolism between 1985 and 2015: a modelling study." Referenced for publicly available bibliographic information and abstract.
   https://doi.org/10.1016/j.lanplh.2026.101546ScienceDirect

4. University of Bath's Nutrition, Exercise, and Metabolism Research Center's LinkedIn public page. Confirmed the researcher's own post and the research institution's sharing. Referenced for the measurement data of 6,756 people, the contribution of population growth, and the explanation of biologically derived carbon. Not a collection of general user reactions.
   https://uk.linkedin.com/company/cnem-bathLinkedIn

5. International Doubly Labeled Water Database: Explanation of the measurement method. Used to supplement the explanation of using stable isotopes to investigate CO₂ production and energy consumption in daily life.
   https://www.dlwdatabase.org/