Metabolic carbon dioxide from human bodies rose 74% worldwide between 1985 and 2015

As bodies convert food into energy they release carbon dioxide, and a University of Bath–led modeling study has estimated that this worldwide metabolic output rose by 74% between 1985 and 2015, reaching 2.05 billion metric tons a year in 2015 for the global human population.

Exhaled carbon comes from food and is largely carbon that plants have recently taken from the atmosphere; fossil fuels release carbon stored underground for millions of years. Gonzalez, lead author from the University of Bath's Center for Exercise, Nutrition and Metabolism, told the university outlet that everyone produces carbon dioxide simply by turning food into energy, that until now there had not been a clear sense of how much that adds up to worldwide, that the increase is mainly because there are more people, and that the result gives scientists another piece of the puzzle when they work out where carbon comes from and where it goes, with the further hope that the information can help them more accurately predict how effective carbon-reduction strategies may be.

Researchers combined thousands of real-world measurements of how much CO2 bodies produce in everyday life, from infancy to old age, with global population and body-weight data, and reported metabolic CO2 contributions across age categories defined as neonates younger than 1 year, juveniles aged 1–17 years, and adults aged 18 years and older. Population growth accounted for more than 60% of the increase between 1985 and 2015; the design points to more people, rather than a major rise in output per person, as the main driver of the global total. The figures are an accounting estimate from the University of Bath–led team, published in The Lancet Planetary Health. That population-led rise would need revision if the everyday metabolic measurements or the population and body-weight inputs fail to represent the global total they are taken to describe.