Researchers at the University of Bath have quantified the amount of carbon dioxide generated by human metabolism on a global scale, according to findings published in The Lancet Planetary Health. The study, led by Professor Javier Gonzalez of the university’s Centre for Exercise, Nutrition and Metabolism, estimates that human metabolic CO2 production reached 2.05 billion metric tons per year in 2015, up from 1.18 billion metric tons in 1985. This represents a 74% increase over the three-decade period.
To arrive at these figures, researchers analyzed thousands of measurements of CO2 production from individuals across different ages and life stages, combined with global population data and body weight statistics. The analysis revealed that population growth accounted for more than 60% of the overall increase in human-generated CO2, while changes in individual metabolic rates played a comparatively minor role. The findings provide scientists with improved baseline data for understanding humanity’s contribution to the global carbon cycle.
The researchers emphasize an important distinction between metabolic CO2 emissions and those from fossil fuel combustion. Carbon dioxide exhaled by humans originates from recently consumed food, with plants having absorbed it from the atmosphere in the near past. In contrast, fossil fuel emissions release carbon that remained sequestered underground for millions of years, fundamentally altering the balance of carbon in Earth’s climate system. Professor Gonzalez noted that the study does not suggest human breathing drives climate change.
Accurate measurement of metabolic CO2 production has practical applications for scientific research. The data helps researchers develop more precise carbon budgets and improve models predicting the effectiveness of emission reduction strategies. Understanding these contributions is particularly relevant in densely populated urban areas, where concentrated human activity can influence local carbon measurements and require more detailed accounting in climate models.
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