Human bodies produce 2 billion metric tons of CO2 a year just by staying alive
Humans collectively produce more than 2 billion tonnes of carbon dioxide annually just by turning food into energy, a 74% increase over three decades largely driven by population growth. Unlike fossil fuel emissions, however, the CO2 we exhale is part of the natural carbon cycle, and scientists say measuring it more accurately could improve climate models.
Key points
- Human metabolism produced 2.05 billion metric tons of CO2 annually by 2015, a 74% rise since 1985.
- Population growth, not higher output per person, drove more than 60% of the increase.
- Researchers say breathing is not driving climate change and differs from burning fossil fuels.
A study led by the University of Bath estimates that carbon dioxide produced by human metabolism rose 74% between 1985 and 2015, reaching 2.05 billion metric tons a year. The research was published in The Lancet Planetary Health.
The team found the rise was mainly due to population growth rather than a large increase in the amount of CO2 each person produces. More than 60% of the increase was attributed to the growing number of people worldwide.
How the study was done
Researchers analyzed thousands of measurements taken from people across the human lifespan, from infants to older adults, to estimate the CO2 the body produces during ordinary daily activities. They combined those findings with worldwide population figures and body weight data.
Global metabolic CO2 output climbed from 1.18 billion metric tons in 1985 to 2.05 billion metric tons in 2015. The researchers say the work could help improve carbon budgets and predictions about how well emissions reduction efforts will work.
We're not saying that breathing is driving climate change.
— Professor Javier Gonzalez
Breathing versus fossil fuels
The researchers stress that CO2 from human metabolism is fundamentally different from emissions from burning coal, oil and natural gas. Most carbon breathed out came from food, which plants absorbed from the atmosphere relatively recently, while fossil fuels hold carbon trapped underground for millions of years.
Professor Javier Gonzalez of the University of Bath's Centre for Exercise, Nutrition and Metabolism said the study does not suggest breathing drives climate change. The team is not recommending that people change their activity or diets to lower the CO2 their bodies produce.
