Human metabolism generated an estimated 2.05 billion metric tons of carbon dioxide in 2015, according to a University of Bath-led study published in The Lancet Planetary Health. The figure represents a 74% increase from the estimated 1.18 billion metric tons produced in 1985.
The researchers said population growth accounted for more than 60% of the increase. Their analysis combined thousands of real-world measurements covering people from infancy to old age with global data on population and body weight. The results indicated that the rise was driven primarily by there being more people, rather than by a substantial increase in the amount of carbon dioxide produced by each individual.
The study focuses on carbon dioxide released when the body converts food into energy. This carbon is largely derived from plants that have recently absorbed it from the atmosphere, making it different from emissions produced by burning fossil fuels, which release carbon stored underground for millions of years.
Javier T. Gonzalez, the study’s lead author from the University of Bath’s Center for Exercise, Nutrition and Metabolism, said the findings provide another element for understanding how carbon moves through the global system. He added that more accurate accounting of human metabolism could improve predictions of how effective carbon-reduction programs may be.
The researchers emphasized that the study does not identify breathing as a cause of climate change, nor does it suggest that people should exercise less or alter their diets. Instead, they said the estimate is intended to help scientists account more precisely for the sources and movement of carbon, especially in densely populated towns and cities.
The study, titled “Accounting for global carbon dioxide production from human metabolism between 1985 and 2015: a modelling study,” was led by Gonzalez and published in 2026. Its DOI is 10.1016/j.lanplh.2026.101546.
Sources: Phys.org.