"Greenhouse gases, of which carbon dioxide is one, are naturally present in the Earth's atmosphere and absorb and release infrared radiation. The five naturally present greenhouse gases are water vapor, ozone, carbon dioxide, methane, and nitrous oxide. Without carbon dioxide and other greenhouse gases, Earth would be much colder and inhospitable to life. Approximately 750 gigatons of carbon dioxide move through the global carbon cycle each year. About 29 gigatons—3.8 percent—is anthropogenic (human-caused) and caused by land use, such as agricultural activities and deforestation, and the burning of fossil fuels. The remaining 96.2 percent is produced naturally by vegetation, land, and oceans."

Tells the whole story.