Humans exhaled an estimated 2.05 billion tonnes of carbon dioxide in 2015, up 74% from 1.18 billion tonnes in 1985, according to a University of Bath announcement of a study in The Lancet Planetary Health. The human breath CO2 estimate comes from thousands of real-world measurements of metabolism from infancy to old age. The increase is 0.87 billion tonnes, a calculation from the two figures.
What the Bath Researchers Measured
The team built the estimate from measurements of how much carbon dioxide people produce from infancy to old age. Population growth accounted for more than 60% of the rise, the university said. The study covers 1985 to 2015 only. Applying the 60% share to the 0.87 billion tonne increase gives more than 0.52 billion tonnes from population growth alone, a calculation from the university’s figures.
Why the Researchers Say It Is Not a Climate Driver
Javier Gonzalez, a professor at Bath’s Centre for Exercise, Nutrition and Metabolism and the study’s lead author, said we are not saying that breathing is driving climate change. The reason is carbon’s source. The carbon people exhale comes from food, and the plants and animals that made the food took that carbon from the air recently. Burning fossil fuels releases carbon that has been underground for millions of years. The university also said the researchers do not suggest that people exercise less or change their diets to cut emissions.
What the Number Is For
The estimate is a model, and the authors present it as an input for carbon accounting. Gonzalez’s group says the figure helps carbon accounting and the accuracy of predictions about carbon reductions.
The fair counterpoint is the researchers’ own: exhaled carbon is part of a short cycle, and fossil fuel carbon is not. More than 60% of the 74% rise comes from population growth, the university said. The University of Bath announcement lists no follow-up study.
