When carbon-based fuels (diesel oil, natural gas [methane], gasoline/petrol, wood, “biofuel”, etc.) are burned, the carbon in the fuels combines with oxygen in the air to create carbon dioxide (CO₂) along with heat. CO₂ in the atmosphere is a so-called “greenhouse gas”, which helps to keep the temperature of the Earth livable. Its natural concentration in the atmosphere has been estimated to have fluctuated between 200 and 300 parts per million (ppm; between 2 and 3 one-hundredths of a percent) over the past hundreds of thousands of years, but it has risen above that since the beginning of the industrial age in the early 1800s – reaching 400 ppm (0.04%) in recent years. Other greenhouse gases include methane (CH₄) and nitrous oxide (N₂O or NOx).
CO₂ in excess of what can be naturally cycled by, e.g., plant life on land and in the sea, as well as by sea water itself, persists in the atmosphere for hundreds – or even thousands – of years. In comparison, CH₄ persists ~10 years, and N₂O ~100 years. Another difference among these greenhouse gases is that over 100 years, CH₄ has 20 times and N₂O 300 times the warming effect of CO₂. Animal agriculture is the main source of both CH₄ and N₂O, and leakage from natural gas drilling is another major source of CH₄. Besides burning carbon-based fuels, humans also contribute to increased CO₂ by deforestation and pollution of the oceans (thus reducing the natural removal of CO₂ from the atmosphere). An excess of greenhouse gases in the atmosphere is thought to contribute to climate-changing warming.
Go to: Carbon emissions.