Every human body produces carbon dioxide simply by converting food into energy. Although the amount released by one person may seem small, the combined output of billions of people adds up to an enormous quantity. A new study led by the University of Bath estimates that carbon dioxide production from human metabolism increased by 74% between 1985 and 2015, reaching 2.05 billion metric tons annually.
The researchers found that the dramatic rise was primarily the result of population growth, rather than a substantial increase in how much CO2 each person produces. The findings could help scientists better understand the global carbon cycle, which describes how carbon moves between the atmosphere, living organisms, oceans, and land. By measuring humanity's contribution more accurately, researchers hope to improve predictions about how well efforts to reduce carbon emissions will work.
Why Human CO2 Emissions Are Different From Fossil Fuels Despite the enormous numbers, the researchers emphasize that the carbon dioxide produced by human metabolism is fundamentally different from the emissions generated by burning fossil fuels. When people breathe out CO2, most of that carbon originally came from the food they consumed. Plants absorbed it from the atmosphere relatively recently, meaning it is already circulating through the natural carbon cycle.
Burning coal, oil, and natural gas is different. These fuels contain carbon that has remained trapped underground for millions of years. Burning them releases that long-stored carbon into the atmosphere, adding to the amount of CO2 circulating through the Earth's climate system.
The new research, published in The Lancet Planetary Health, was led by Professor Javier Gonzalez of the University of Bath's Centre for Exercise, Nutrition and Metabolism. The team calculated that global CO2 production from human metabolism climbed from 1.18 billion metric tons in 1985 to 2.05 billion metric tons in 2015. More than 60% of that increase could be attributed to the growing number of people worldwide.
"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.
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