# University of Bath: human metabolic CO2 rose 74% in 1985–2015 to 2,050 million tonnes a year

- Published: 2026-11-15 15:00 UTC
- Section: Planet › Climate
- Tags: human metabolic CO2, exhaled carbon dioxide, carbon cycle, University of Bath study, world population growth, carbon accounting, Javier González, The Lancet Planetary Health
- URL: https://realtech.media/news/rt-ff5c6612379dc6c5c63d3a31_university_of_bath/

**Researchers at the University of Bath estimated CO2 from human metabolism at 2,050 million tonnes a year in 2015. Over 60% of the rise comes from population growth.**

![University of Bath: human metabolic CO2 rose 74% in 1985–2015 to 2,050 million tonnes a year](https://realtech.media/media/2026/11/d41c9aa8f6e91920.jpg)
*consalud.es*

A team at the Centre for Exercise, Nutrition and Metabolism, University of Bath, calculated how much carbon dioxide the human body produces when it converts food into energy. According to the authors, the figure rose by 74% between 1985 and 2015, from 1,180 million tonnes to 2,050 million tonnes a year. The study was published in The Lancet Planetary Health and led by Professor Javier González; the results were reported by consalud.es [1].

More than 60% of the increase is attributed to growth of the world population [1]. The authors conclude that the rise stems mainly from there being more people, not from a significant increase in the CO2 produced by each individual [1].

## How the estimate was made

The researchers collected thousands of measurements taken on people of different ages, from children to older adults, showing how much CO2 the body produces during daily activities. They then combined these data with figures on world population change and body weight [1].

The authors say that more precise estimates can help the scientific community understand how carbon circulates on the planet, where it comes from and where it goes. They describe human metabolism as a relevant part of the carbon cycle, especially in cities and densely populated areas [1].

## Metabolic CO2 versus fossil fuels

The origin of exhaled CO2 differs from that of fossil fuel emissions. In the first case the carbon comes from food and was, to a large extent, recently absorbed from the atmosphere by plants. Fossil fuels release carbon that had been stored underground for millions of years [1].

The researchers stress that breathing is not an environmental problem to be avoided. The aim of the work is to improve the accounting of carbon emissions, not to suggest that people reduce physical activity or change their diet [1].

According to González, the data add one more piece to the puzzle of where carbon comes from and where it goes. He said this knowledge could help improve the accuracy of predictions for carbon reduction programmes [1].

## Sources

1. [consalud.es](https://www.consalud.es/pacientes/el-co-que-exhalamos-al-respirar-crecio-un-74-en-tres-decadas-impulsado-por-el-aumento-de-la-poblacion.html)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-ff5c6612379dc6c5c63d3a31_university_of_bath/