Human Metabolism Produces 2.05 Billion Tons of CO₂ Annually, Study Finds

A new study reveals that the amount of carbon dioxide produced through human metabolism has increased substantially over three decades.

Human metabolism produces carbon dioxide as the body converts food into energy, contributing to the natural movement of carbon through the environment.

The carbon dioxide generated as human bodies convert food into energy increased by 74% between 1985 and 2015, according to a University of Bath-led study published in The Lancet Planetary Health and reported by SciTechDaily.

By 2015, the global total had reached an estimated 2.05 billion metric tons (2.26 billion U.S. tons) annually, highlighting a substantial component of the Earth's carbon cycle that scientists had not previously quantified on this scale.

Unlike emissions from burning fossil fuels, the carbon dioxide humans exhale largely comes from carbon recently absorbed from the atmosphere by plants and transferred through food.

Burning coal, oil, and natural gas, by contrast, releases carbon that has been stored underground for millions of years, adding it to the active carbon cycle.

Published in The Lancet Planetary Health, the study found that annual CO₂ production from human metabolism rose from 1.18 billion metric tons (1.30 billion U.S. tons) in 1985 to 2.05 billion metric tons (2.26 billion U.S. tons) in 2015.

More than 60% of that increase was attributable to population growth rather than a substantial rise in the amount of carbon dioxide produced by each individual.

Professor Javier Gonzalez, who led the research at the University of Bath's Centre for Exercise, Nutrition and Metabolism, explained: "We all produce carbon dioxide simply by turning food into energy, but until now we haven't had a good idea how much that adds up to worldwide. What we've found is that the increase is mainly because there are more of us. This gives scientists one more piece of the puzzle when working out where carbon comes from and where it goes. Ultimately, this information can help scientists more accurately predict how effective carbon reduction strategies may be."