How much CO2 do you exhale just by living?
An average adult exhales roughly 200 mL of CO2 per minute at rest, totaling about 0.9 kg (900 g) of CO2 per day or ~330 kg per year. During vigorous exercise, this can increase 4-10x. However, human respiration is considered carbon-neutral because the CO2 we exhale comes from recently photosynthesized carbon in the food we eat — it was absorbed from the atmosphere by plants within the past few years and will be re-absorbed. This is fundamentally different from fossil fuel emissions, which release carbon stored underground for millions of years. The 8 billion humans on Earth collectively exhale about 2.6 billion tonnes of CO2 annually, but this is already part of the natural carbon cycle and does not contribute to net atmospheric CO2 increase.