greenhouse effect

What is the 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), and water vapor (H2O), in the atmosphere that allow incoming sunlight to pass through but absorb heat radiated back from the Earth's surface, resulting in higher temperatures. The greenhouse effect gets its name from what actually happens 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 is of longer wavelength and is unable to pass through the glass barrier, maintaining a warm temperature similar to a car’s warming interior when parked in sunlight. 

Schematic of the greenhouse effect 
Schematic of the Greenhouse Effect  

The Earth's natural greenhouse effect is similar. 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 surface or absorbed by greenhouse gases (GHGs) that re-radiate longer wavelength radiation back to Earth's surface. These GHGs trap the sun’s energy within the atmosphere to warm the planet.

GHGs, such as CO2, CH4, H2O, and nitrous oxide (N2O), can be compared to the glass panes in the greenhouse example, as they trap indirect heat from the sun. GHGs do not have a negative effect when present in natural amounts; in fact, the Earth would be 0°F (-18°C) without them.

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