The average human exhales about 2.3 pounds of carbon dioxide on an average day. (The exact quantity depends on your activity level—a person engaged in vigorous exercise produces up to eight times as much CO2 as his sedentary brethren.)
~7,000,000,000 human beings X 2.3lbs. = 16.1 billion or ~ 8million Tons of CO2 emitted by humans every day.
Humans are carbon-based. I wonder if they're not.