# University of Bath: human metabolism produced 2.05 billion tonnes of CO₂ in 2015, up 74% since 1985

- Published: 2026-11-14 00:54 UTC
- Section: Planet › Climate
- Tags: human metabolism CO₂, carbon dioxide from respiration, global carbon accounting, University of Bath study, doubly labelled water, population growth and CO₂, Javier Gonzalez, carbon cycle
- URL: https://realtech.media/news/rt-bbf547d194b909fdf676bceb_university_of_bath/

**A modelling study estimates that CO₂ produced as human bodies turn food into energy reached 2.05 billion tonnes a year, which refines global carbon accounting.**

![University of Bath: human metabolism produced 2.05 billion tonnes of CO₂ in 2015, up 74% since 1985](https://realtech.media/media/2026/11/11ed2cbd68a0bcb8.jpg)
*bioengineer.org*

A study led by the University of Bath has estimated that the carbon dioxide produced by humans as their bodies turn food into energy rose by 74% between 1985 and 2015, reaching 2.05 billion tonnes a year, according to eurekalert.org [1]. The paper was published in The Lancet Planetary Health and led by Professor Javier Gonzalez of the university's Centre for Exercise, Nutrition and Metabolism [1]. The global amount grew from 1.18 billion tonnes in 1985 to 2.05 billion tonnes in 2015 [1].

## Data and result

The researchers used thousands of real-world measurements of people from infancy to old age, showing how much CO₂ their bodies produced during everyday life [1]. They combined these with global population and body-weight data. The work is a modelling study, and the authors acted on behalf of the IAEA Doubly Labelled Water Database Consortium writing group [1].

Population growth accounted for more than 60% of the increase [1]. According to the authors, the main reason for the rise was the growing number of people, not a major increase in the amount produced by each person [1].

The authors come from the University of Bath, Manchester Metropolitan University, Liverpool John Moores University, Auckland University of Technology, the University of Castilla-La Mancha and the Chulabhorn Royal Academy [1].

## Carbon accounting

The CO₂ people breathe out is not the same as emissions from burning fossil fuels [1]. The carbon we exhale comes from the food we eat and is largely carbon that plants have recently taken from the atmosphere [1]. Fossil fuels, by contrast, release carbon that has been stored underground for millions of years [1].

Gonzalez said that until now there was no good estimate of how much human CO₂ production adds up to worldwide [1]. The authors say the figure gives scientists one more piece for working out where carbon comes from and where it goes. Human metabolism is a sizeable part of that movement, particularly in heavily populated towns and cities [1].

The researchers stress that breathing is not driving climate change. The findings concern carbon accounting and do not suggest that people should exercise less or change what they eat [1]. According to Gonzalez, a clearer picture of human CO₂ production can help improve the accuracy of predictions for carbon reduction programmes [1].

## Sources

1. [eurekalert.org](https://www.eurekalert.org/news-releases/1149633)
2. [bioengineer.org](https://bioengineer.org/human-metabolism-generates-over-two-billion-tonnes-of-carbon-dioxide-annually)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-bbf547d194b909fdf676bceb_university_of_bath/