Carbon Dioxide 101


  Greenhouse Effect
  Greenhouse Effect

The greenhouse effect is used to describe the phenomenon whereby the Earth's atmosphere traps solar radiation, caused by the presence of gases, such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor (H2O). Collectively, these gases are referred to as greenhouse gases (GHGs). The greenhouse effect gets its name from the process that actually occurs in a greenhouse. In a greenhouse, short wavelength visible sunlight shines through the glass panes and warms the air and the plants inside. The radiation emitted from the heated objects inside the greenhouse are of longer wavelength and therefore are unable to pass through the glass barrier, maintaining a warm temperature in the greenhouse.

Schematic of the Greenhouse Effect  

The Earth's natural greenhouse effect acts similarly. Sunlight that enters the atmosphere is either reflected, absorbed, or simply passes through. The sunlight that passes through the atmosphere is either absorbed by the Earth's surface or reflected back into space. The Earth's surface heats up after absorbing this sunlight, and emits long wavelength radiation back into the atmosphere. Some of this radiation passes through the atmosphere and into space, but the rest of it is either reflected back to the Earth’s surface or absorbed by atmospheric GHGs that re-radiate longer wavelengths back to Earth's surface. These GHGs trap the sun’s energy within the atmosphere, warming the planet.

GHGs can be compared to the glass panes in the greenhouse example, since they trap indirect heat from the sun. Carbon dioxide and other GHGs help create and maintain the natural greenhouse effect that keeps Earth hospitable to life. GHGs do not have a negative effect when present in natural amounts; in fact, the Earth’s average temperatures would be much cooler without them.

Myth: GHGs like CO2 should be completely removed from the atmosphere.
Reality: GHGs like CO2, within certain concentration ranges, help to maintain a global temperature hospitable to life.

Where does all of the CO2 come from?