Human metabolism produced 2.05 billion tonnes of CO₂ a year by 2015
A University of Bath-led study estimates that CO₂ produced as people convert food into energy rose 74%, from 1.18 billion tonnes in 1985 to 2.05 billion tonnes in 2015. Published in The Lancet Planetary Health, the study attributes more than 60% of the increase to population growth and says the findings can improve carbon accounting; exhaled CO₂ is largely carbon recently absorbed by plants, unlike emissions from burning fossil fuels.
Bottom line — Population growth drove more than 60% of the rise, but the researchers say breathing is not driving climate change.
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The University of Bath researchers combined thousands of real-world measurements, from infants to older adults, with global population and body-weight data.
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The study found no major rise in the amount of CO₂ produced by each person; population growth was the main factor.
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Lead author Javier Gonzalez said better accounting could help scientists assess the effectiveness of carbon-reduction strategies.
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The researchers said the findings are about tracking carbon flows, not a reason to exercise less or change diets.