Human Metabolism Produced 2 Billion Tonnes of CO2 in 2015
People exhale a lot of carbon dioxide, and the total is growing. A University of Bath study puts it at 2.05 billion metric tons a year for 2015.
The numbers behind the estimate
The figure is 74% above the 1.18 billion metric tons estimated for 1985. The work was led by Professor Javier Gonzalez and published in The Lancet Planetary Health.
Population growth explains more than 60% of the rise. The team started from thousands of measurements made in real life on people of every age, from infants to the elderly, recording the CO2 their bodies gave off day to day. Global population and body-weight figures were then added to scale this up to the whole world.
Not the same as fossil fuel emissions
The study draws a clear line. Exhaled carbon comes from food, and most of it was pulled out of the air by plants not long ago. Burning fossil fuels, by contrast, adds to the air carbon that had been locked underground for millions of years.
Gonzalez said the authors are not saying that breathing is driving climate change. The findings are about carbon accounting, and the researchers do not say anyone needs to exercise less or alter their diet.
Why the number matters to scientists
Gonzalez said that until now there was no good idea of how much human metabolism adds up to worldwide. Pinning it down gives scientists another input for tracing the sources and destinations of carbon.
Human bodies account for a sizable share of that movement, most of all in crowded cities. A better figure could make predictions about carbon reduction programmes more accurate.
Our take
The estimate covers the years up to 2015, so it says nothing about the period since. How much weight climate models will give to this flow is still an open question.
Source: Phys.org