Human Metabolism's CO₂ Output Could Improve Global Carbon Accounting, Researchers Say

Researchers at the University of Bath's Centre for Exercise, Nutrition and Metabolism, led by Professor Javier Gonzalez, say that human metabolism contributes to the continuous movement of carbon through the environment, particularly in densely populated cities, SciTechDaily reported.

Researchers say accounting for carbon dioxide produced through human metabolism could improve global carbon budgets and climate models.

Accounting for this biological activity could help researchers develop more accurate carbon budgets and better assess the effectiveness of strategies designed to reduce emissions.

The researchers emphasize that their findings do not suggest people should exercise less, change their diets, or attempt to reduce the carbon dioxide they breathe out.

Instead, the research aims to improve scientific measurements of carbon movement and provide a more complete understanding of the global carbon cycle.

To estimate global CO₂ production from human metabolism, the researchers analyzed thousands of real-world measurements of carbon dioxide production in people ranging from infants to older adults.

They combined these findings with worldwide population and body-weight data to calculate how human metabolic activity changed between 1985 and 2015.

The study estimated that human metabolism produced approximately 2.05 billion metric tons of carbon dioxide annually by 2015, representing a 74% increase from the 1.18 billion metric tons estimated in 1985.

More than 60% of the increase was attributed to population growth. Human metabolism contributes to the continuous movement of carbon through the environment.

Accounting for this activity, particularly in heavily populated towns and cities, could help scientists improve estimates of global carbon flows.

However, the researchers stress that carbon dioxide exhaled by humans is fundamentally different from emissions produced by burning fossil fuels.

The carbon in exhaled CO₂ largely originates from food, which contains carbon recently absorbed from the atmosphere by plants. Fossil-fuel combustion, on the other hand, releases carbon stored underground for millions of years.

Professor Gonzalez stressed this distinction: "The important thing is that the carbon dioxide we breathe out is not the same as burning fossil fuels. We're not saying that breathing is driving climate change. What this study does is give us a much clearer picture of how much CO₂ people produce around the world, and how that is changing as the population grows. This understanding can help improve the accuracy of predictions of carbon reduction programs."

The researchers say that incorporating human metabolic CO₂ into carbon accounting could give scientists a more comprehensive understanding of the movement of carbon through the environment and help improve assessments of climate-related policies.