Greenhouse effect, 2010-2017
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Greenhouse effect refers to the process by which the Earth’s surface absorbs incoming solar energy and then emits energy as infrared radiation. Certain gases in the atmosphere absorb and re-emit a portion of this infrared radiation, directing some of it back toward the surface. This exchange of energy warms the lower atmosphere and surface and helps maintain the planet’s energy balance. The greenhouse effect is one of several climate forcings—factors that influence Earth’s climate—along with variations in solar energy, volcanic activity, and atmospheric aerosols.[1][2]
Background
Sunlight reaches Earth primarily as visible and ultraviolet radiation. Roughly one-third of the incoming solar energy is reflected back to space; the remainder is absorbed by the surface and atmosphere. On average, Earth returns the absorbed energy to space by emitting infrared radiation. Greenhouse gases and clouds absorb some of this infrared radiation and re-emit it in all directions, including back toward the surface. This natural greenhouse effect raises Earth’s average surface temperature relative to what it would be without these gases; without it, the average surface temperature is estimated to be about −18 °C (0 °F).[1][2][3]
Gases that contribute to the greenhouse effect include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. These molecules, which have three or more atoms, can absorb infrared radiation due to their vibrational modes and then re-emit that energy. Part of the re-emitted energy remains in the atmosphere or returns to the surface, influencing temperature.[1][2]
Water vapor and carbon dioxide are major contributors; methane, nitrous oxide, ozone, and others also play roles at lower concentrations. By contrast, nitrogen and oxygen—the most abundant atmospheric gases—absorb little infrared radiation and have minimal greenhouse effect. Atmospheric concentrations of greenhouse gases vary due to natural processes and human activities, including emissions and uptake by oceans, ice, vegetation, and other components of the Earth system.[4][5]
The image below shows how the greenhouse effect is produced.
Impact on climate and global temperature
Changes in greenhouse gas concentrations are one climate forcing among several. Other forcings include variations in solar output, volcanic eruptions that inject particles into the atmosphere, and aerosols from natural and human sources. Researchers assess how these forcings influence global temperature over different time periods and how they compare in magnitude.[6][7]
Feedbacks are processes that can amplify (positive feedback) or reduce (negative feedback) the effect of a forcing such as the greenhouse effect. Examples include:[8][9]
- Clouds: Clouds reflect back into space approximately one-third of all sunlight that hits the Earth's atmosphere. Increased cloudiness caused by more water in the atmosphere can limit the amount of sunlight from hitting the Earth's surface, resulting in less absorbed heat and less warming.
- Precipitation: A warmer atmosphere that holds more water can increase precipitation, though not in all regions. Changes in precipitation patterns can result in more water available for plants, which remove carbon dioxide (a greenhouse gas, also known as CO2) from the atmosphere. Increased plant growth could result in more CO2 absorption from the atmosphere and thus less warming.
- Forested areas: As negative feedbacks, forests, trees, and other plants remove CO2 from the atmosphere and thus can reduce warming that may be the result of increased CO2 in the atmosphere. However, forests and plants may also be cut down so that land is cleared for agriculture or other uses, which results in less CO2 absorption.
- Ice: Compared to ocean surfaces, which are dark and absorb heat more quickly, ice is white and thus quickly and more easily reflects sunlight. More ice and glaciers result in greater heat reflection and thus less warming. However, greater sea ice and glacier melting reduces this reflection and allows the ocean to absorb more heat and accelerate warming. This process is known as the ice albedo feedback.
See also
Footnotes
- ↑ 1.0 1.1 1.2 United Nations Intergovernmental Panel on Climate Change, "What is the Greenhouse Effect?" accessed June 30, 2017
- ↑ 2.0 2.1 2.2 American Chemical Society, "What is the Greenhouse Effect?" accessed June 20, 2017
- ↑ UCAR Center for Science Education, "The Greenhouse Effect," accessed June 30, 2017
- ↑ Science News for Students, "Explainer: Global warming and the greenhouse effect," May 27, 2010
- ↑ U.S. Energy Information Administration, "What are greenhouse gases and how do they affect the climate?" accessed July 11, 2017
- ↑ AccuWeather, "What are Climate Forcings?" accessed July 22, 2017
- ↑ Climate of Concern, "Basics of Climate Science - Feedbacks," accessed July 11, 2017
- ↑ OSS Foundation, "Climate Feedback/Sensitivity," accessed July 20, 2017
- ↑ National Aeronautics and Space Administration, "The Study of Earth as an Integrated System," accessed July 22, 2017
