Global human metabolic CO2 was estimated at 2.05 billion tonnes in 2015

The study combined thousands of real-world metabolic measurements from infancy to old age with global population and body-weight data, estimating a rise from 1.18 billion tonnes in 1985 to 2.05 billion in 2015. Exhaled carbon comes from food and mostly belongs to the short cycle recently absorbed by plants, unlike ancient underground carbon released by fossil fuels. The purpose is better urban and global carbon-flow accounting, not asking people to breathe or exercise less.