greenhouse effect

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greenhouse effect

Energy radiated by the sun converts to heat when it reaches earth. Some heat is reflected back through the atmosphere, while some is absorbed by atmospheric gases and radiated back to earth. (Precision Graphics)

1. The phenomenon whereby the earth's atmosphere traps solar radiation, caused by the presence in the atmosphere of gases such as carbon dioxide, water vapor, and methane that allow incoming sunlight to pass through but absorb heat radiated back from the earth's surface.
2. A similar retention of solar radiation, as by another planet or in a solar panel.

The ability of a planetary atmosphere to inhibit heat loss from the planet's surface, thereby enhancing the surface warming that is produced by the absorption of solar radiation. For the greenhouse effect to work efficiently, the planet's atmosphere must be relatively transparent to sunlight at visible wavelengths so that significant amounts of solar radiation can penetrate to the ground. Also, the atmosphere must be opaque at thermal wavelengths to prevent thermal radiation emitted by the ground from escaping directly to space. The principle is similar to a thermal blanket, which also limits heat loss by conduction and convection. In recent decades the term has also become associated with the issues of global warming and climate change induced by human activity. See also Atmosphere; Solar radiation.

Basic understanding of the greenhouse effect dates back to the 1820s, when the French mathematician and physicist Joseph Fourier performed experiments on atmospheric heat flow and pondered the question of how the Earth stays warm enough for plant and animal life to thrive; and to the 1860s, when the Irish physicist John Tyndall demonstrated by means of quantitative spectroscopy that common atmospheric trace gases, such as water vapor, ozone, and carbon dioxide, are strong absorbers and emitters of thermal radiant energy but are transparent to visible sunlight. It was clear to Tyndall that water vapor was the strongest absorber of thermal radiation and, therefore, the most influential atmospheric gas controlling the Earth's surface temperature. The principal components of air, nitrogen and oxygen, were found to be radiatively inactive, serving instead as the atmospheric framework where water vapor and carbon dioxide can exert their influence.

The impact of water vapor behavior was noted by the American geologist Thomas Chamberlin who, in 1905, described the greenhouse contribution by water vapor as a positive feedback mechanism. Surface heating due to another agent, such as carbon dioxide or solar radiation, raises the surface temperature and evaporates more water vapor which, in turn, produces additional heating and further evaporation. When the heat source is taken away, excess water vapor precipitates from the atmosphere, reducing its contribution to the greenhouse effect to produce further cooling. This feedback interaction converges and, in the process, achieves a significantly larger temperature change than would be the case if the amount of atmospheric water vapor had remained constant. The net result is that carbon dioxide becomes the controlling factor of long-term change in the terrestrial greenhouse effect, but the resulting change in temperature is magnified by the positive feedback action of water vapor.

Besides water vapor, many other feedback mechanisms operate in the Earth's climate system and impact the sensitivity of the climate response to an applied radiative forcing. Determining the relative strengths of feedback interactions between clouds, aerosols, snow, ice, and vegetation, including the effects of energy exchange between the atmosphere and ocean, is an actively pursued research topic in current climate modeling. See also Climate modification.

The warming of the atmosphere as some of its gases absorb the heat given out by the earth. Short-wave radiation from the sun warms the earth during daylight hours, but this heat is balanced by outgoing long-wave radiation over the entire 24-hour period. Much of this radiation is absorbed by atmospheric gases, most notably water vapour, carbon dioxide, and ozone, but also by methane and chloro-fluorocarbons. All of these may be called greenhouse gases. Without this absorption, which is also known as counter-radiation, the temperature of the atmosphere would fall by 30-40 °C.

Through human agency, such as the clearance of rain forest, or the increased rearing of livestock, the concentration of greenhouse gases in the atmosphere is increasing; measurements taken at Mauna Loa, Hawaii, show that the concentration of atmospheric CO₂, for example, increased by 8% between 1959 and 1983, mostly because of the increased use of fossil fuels. It would follow, therefore, that increased concentrations of such greenhouse gases would lead to a rise in global temperatures, and, indeed, global mean temperatures have increased by 0.3 to 0.7 °K over the last century, but the cause of this temperature rise has not been unequivocally put down to the increase in greenhouse gases. It may be that the uptake of CO₂ by the oceans actually increases with higher temperatures. Others argue that increased concentrations of CO₂ foster improved rates of photosynthesis in plants, so that faster-growing trees, for example, might partially offset increased concentrations of carbon dioxide. Thus, general models of the effect of growing greenhouse gas levels do not give unequivocal predictions of future trends in climates.

The analogy with a greenhouse is not perfect, since a greenhouse retains heat through lack of movement in the air as well as by absorbing counter-radiation.

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Some incoming sunlight is reflected by the Earth's atmosphere and surface, but most is absorbed by … (credit: © Merriam-Webster Inc.)

Warming of the Earth's surface and lower atmosphere caused by water vapour, carbon dioxide, and other trace gases in the atmosphere. Visible light from the Sun heats the Earth's surface. Part of this energy is radiated back into the atmosphere in the form of infrared radiation, much of which is absorbed by molecules of carbon dioxide and water vapour in the atmosphere and reradiated toward the surface as more heat. (Despite the name, the greenhouse effect is different from the warming in a greenhouse, where panes of glass allow the passage of visible light but hold heat inside the building by trapping warmed air.) The absorption of infrared radiation causes the Earth's surface and lower atmosphere to warm more than they otherwise would, making the Earth's surface habitable. An increase in atmospheric carbon dioxide caused by widespread combustion of fossil fuels may intensify the greenhouse effect and cause long-term climatic changes. Likewise, an increase in atmospheric concentrations of other trace greenhouse gases such as chlorofluorocarbons, nitrous oxide, and methane resulting from human activities may also intensify the greenhouse effect. From the beginning of the Industrial Revolution through the end of the 20th century, the amount of carbon dioxide in the atmosphere increased 30% and the amount of methane more than doubled. It is also estimated that the U.S. is responsible for about one-fifth of all human-produced greenhouse-gas emissions. See also global warming.

For more information on greenhouse effect, visit Britannica.com.

The greenhouse effect is a warming near the Earth's surface that results when the Earth's atmosphere traps the sun's heat. The atmosphere acts much like the glass walls and roof of a greenhouse. The effect was described by John Tyndall (1820-1893) in 1861. It was given the greenhouse analogy much later in 1896 by the Swedish chemist Svante Arrhenius (1859-1927). The greenhouse effect is what makes the Earth habitable. Without the presence of water vapor, carbon dioxide, and other gases in the atmosphere, too much heat would escape and the Earth would be too cold to sustain life. Carbon dioxide, methane, nitrous oxide, and other greenhouse gases absorb the infrared radiation rising from the Earth and hold this heat in the atmosphere instead of reflecting it back into space.

In the 20th century, the increased build-up of carbon dioxide, caused by the burning of fossil fuels, has been a matter of concern. There is some controversy concerning whether the increase noted in the Earth's average temperature is due to the increased amount of carbon dioxide and other gases, or is due to other causes. Volcanic activity, destruction of the rainforests, use of aerosols, and increased agricultural activity may also be contributing factors.

A term used to describe the heating of the atmosphere owing to the presence of carbon dioxide and other gases. Without the presence of these gases, heat from the sun would return to space in the form of infrared radiation. Carbon dioxide and other gases absorb some of this radiation and prevent its release, thereby warming the Earth. This is an effect analogous to what happens in a greenhouse, where glass traps the infrared radiation and warms the air.

A schematic representation of the exchanges of energy between outer space, the Earth's atmosphere, and the Earth's surface. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect.

The greenhouse effect is the heating of the surface of a planet or moon due to the presence of an atmosphere containing gases that absorb and emit infrared radiation.^[1] Thus, greenhouse gases trap heat within the surface-troposphere system.^[2] This mechanism is fundamentally different from that of an actual greenhouse, which works by isolating warm air inside the structure so that heat is not lost by convection. The greenhouse effect was discovered by Joseph Fourier in 1824, first reliably experimented on by John Tyndall in 1858, and first reported quantitatively by Svante Arrhenius in 1896.^[3]

In the absence of the greenhouse effect and an atmosphere, the Earth's average surface temperature^[4] of 14 °C (57 °F) could be as low as −18 °C (−0.4 °F), the black body temperature of the Earth.^[5][6][7] Global warming, a recent warming of the Earth's surface and lower atmosphere,^[8] is believed to be the result of an "enhanced greenhouse effect" mostly (more than 50%) due to human-produced increases in atmospheric greenhouse gases.^[9] This human induced part is refered to as anthropogenic global warming (AGW).

Contents 1 Basic mechanism 2 Greenhouse gases 3 Anthropogenic greenhouse effect 4 Real greenhouses 5 Bodies other than Earth 6 See also 7 Literature 8 References

Basic mechanism

See also: Radiative forcing

The Earth receives energy from the Sun mostly in the form of visible light and nearby wavelengths. About 50% of the sun's energy is absorbed at the Earth's surface. Like all bodies with a temperature above absolute zero the Earth's surface radiates energy in the infrared range. Greenhouse gases in the atmosphere absorb most of the infrared radiation emitted by the surface and pass the absorbed heat to other atmospheric gases through molecular collisions. The greenhouse gases also radiate in the infrared range. Radiation is emitted both upward, with part escaping to space, and downward toward Earth's surface. The surface and lower atmosphere are warmed by the part of the energy that is radiated downward, making our life on earth possible.^[5]

Greenhouse gases

Main article: Greenhouse gas

In order, Earth's most abundant greenhouse gases are:

• water vapor
• carbon dioxide
• methane
• nitrous oxide
• ozone
• CFCs

Real Climate ranks by their contribution to the greenhouse effect:^[10]

• water vapor, which contributes 36–70%
• carbon dioxide, which contributes 9–26%
• methane, which contributes 4–9%
• ozone, which contributes 3–7%

The major non-gas contributor to the Earth's greenhouse effect, clouds, also absorb and emit infrared radiation and thus have an effect on radiative properties of the atmosphere.^[11]

Anthropogenic greenhouse effect

Main article: Global warming

Carbon dioxide is the human-produced greenhouse gas that contributes most of radiative forcing from human activity. CO₂ is produced by fossil fuel burning and other human activities such as cement production and tropical deforestation.^[12] Measurements of CO₂ from the Mauna Loa observatory show that concentrations have increased from about 313 ppm ^[13] in 1960 to about 383 ppm in 2009. The current observed amount of CO₂ exceeds the geological record maxima (~300 ppm) from ice core data.^[14] The effect of combustion-produced carbon dioxide on the global climate, a special case of the greenhouse effect first described in 1896 by Svante Arrhenius, has also been called the Callendar effect.

Because it is a greenhouse gas, elevated CO₂ levels will contribute to additional absorption and emission of thermal infrared in the atmosphere, which could contribute to net warming. In fact, according to Assessment Reports from the Intergovernmental Panel on Climate Change, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations".^[15]

Over the past 800,000 years,^[16] ice core data shows unambiguously that carbon dioxide has varied from values as low as 180 parts per million (ppm) to the pre-industrial level of 270ppm.^[17] Certain paleoclimatologists consider variations in carbon dioxide to be a fundamental factor in controlling climate variations over this time scale.^[18]

Real greenhouses

Main article: Solar greenhouse (technical)

A modern Greenhouse in RHS Wisley

The term "greenhouse effect" can be a source of confusion as actual greenhouses do not function by the same mechanism the atmosphere does. Various materials at times imply incorrectly that they do, or do not make the distinction between the processes of radiation and convection^[19].

The term 'greenhouse effect' originally came from the greenhouses used for gardening, but as mentioned the mechanism for greenhouses operates differently.^[20] Many sources make the "heat trapping" analogy of how a greenhouse limits convection to how the atmosphere performs a similar function through the different mechanism of infrared absorbing gases.^[21]

A greenhouse is usually built of glass, plastic, or a plastic-type material. It heats up mainly because the sun warms the ground inside it, which then warms the air in the greenhouse. The air continues to heat because it is confined within the greenhouse, unlike the environment outside the greenhouse where warm air near the surface rises and mixes with cooler air aloft. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably. It has also been demonstrated experimentally (Wood, 1909) that a "greenhouse" with a cover of rock salt heats up an enclosure similarly to one with a glass cover.^[22] Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection.^[23][20]

Bodies other than Earth

In our solar system, Mars, Venus, and the moon Titan also exhibit greenhouse effects. Titan has an anti-greenhouse effect, in that its atmosphere absorbs solar radiation but is relatively transparent to infrared radiation. Pluto also exhibits behavior similar to the anti-greenhouse effect.^[24][25][26]

A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into the atmosphere.^[27] A runaway greenhouse effect involving carbon dioxide and water vapor may have occurred on Venus.^[28]

See also

Wikibooks has a book on the topic of Climate Change

Wikiversity has learning materials about Topic:Climate change

• Anti-greenhouse effect
• Climate change
• Climate forcing
• Earth's energy budget
• Earth's radiation balance
• Global dimming
• Global warming
• Idealized greenhouse model

Literature

• Earth Radiation Budget, http://marine.rutgers.edu/mrs/education/class/yuri/erb.html
• Fleagle, RG and Businger, JA: An introduction to atmospheric physics, 2nd edition, 1980
• IPCC assessment reports, see http://www.ipcc.ch/
• Ann Henderson-Sellers and McGuffie, K: A climate modelling primer (quote: Greenhouse effect: the effect of the atmosphere in re-readiating longwave radiation back to the surface of the Earth. It has nothing to do with glasshouses, which trap warm air at the surface).
• Idso, S.B.: "Carbon Dioxide: friend or foe," 1982 (quote: ...the phraseology is somewhat in appropriate, since CO₂ does not warm the planet in a manner analogous to the way in which a greenhouse keeps its interior warm).
• Kiehl, J.T., and Trenberth, K. (1997). "Earth's annual mean global energy budget," Bulletin of the American Meteorological Society '78' (2), 197–208.

References

1. ^ [1] IPCC AR4 SYR Appendix Glossary
2. ^ A concise description of the greenhouse effect is given in the Intergovernmental Panel on Climate Change Fourth Assessment Report, "What is the Greenhouse Effect?" IIPCC Fourth Assessment Report, Chapter 1, page 115: "To balance the absorbed incoming [solar] energy, the Earth must, on average, radiate the same amount of energy back to space. Because the Earth is much colder than the Sun, it radiates at much longer wavelengths, primarily in the infrared part of the spectrum (see Figure 1). Much of this thermal radiation emitted by the land and ocean is absorbed by the atmosphere, including clouds, and reradiated back to Earth. This is called the greenhouse effect."
   Stephen H. Schneider, in Geosphere-biosphere Interactions and Climate, Lennart O. Bengtsson and Claus U. Hammer, eds., Cambridge University Press, 2001, ISBN 0521782384, pp. 90-91.
   E. Claussen, V. A. Cochran, and D. P. Davis, Climate Change: Science, Strategies, & Solutions, University of Michigan, 2001. p. 373.
   A. Allaby and M. Allaby, A Dictionary of Earth Sciences, Oxford University Press, 1999, ISBN 0192800795, p. 244.
3. ^ Annual Reviews (requires registration)
4. ^ The elusive "absolute surface air temperature," see GISS discussion
5. ^ ^{a b} Intergovernmental Panel on Climate Change Fourth Assessment Report. Chapter 1: Historical overview of climate change science page 97
6. ^ V1003 Science and Society - Solar Radiation
7. ^ Solar Radiation and the Earth's Energy Balance
8. ^ Merged land air and sea surface temperature data set
9. ^ The enhanced greenhouse effect
10. ^ "Water vapour: feedback or forcing?". RealClimate. 6 April 2005. http://www.realclimate.org/index.php?p=142. Retrieved 2006-05-01. 
11. ^ Kiehl, J. T.; Kevin E. Trenberth (February 1997). "Earth’s Annual Global Mean Energy Budget" (PDF). Bulletin of the American Meteorological Society 78 (2): 197–208. doi:10.1175/1520-0477(1997)078<0197:EAGMEB>2.0.CO;2. http://www.atmo.arizona.edu/students/courselinks/spring04/atmo451b/pdf/RadiationBudget.pdf. Retrieved 2006-05-01. 
12. ^ IPCC Fourth Assessment Report, Working Group I Report "The Physical Science Basis" Chapter 7
13. ^ "Atmospheric Carbon Dioxide - Mauna Loa". NOAA. http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_data_mlo.html. 
14. ^ Hansen, J., Climatic Change, 68, 269, 2005 ISSN 0165-0009
15. ^ IPCC Fourth Assessment Report Synthesis Report: Summary for Policymakers (p. 5)
16. ^ BBC NEWS | Science/Nature | Deep ice tells long climate story
17. ^ Chemical & Engineering News: Latest News - Ice Core Record Extended
18. ^ Bowen, Mark; Thin Ice: Unlocking the Secrets of Climate in the World's Highest Mountains; Owl Books, 2005.
19. ^ EPA Climate Change Site
20. ^ ^{a b} Schroeder, Daniel V. (2000). An introduction to thermal physics. San Francisco, California: Addison-Wesley. pp. 305–307. ISBN 0-321-27779-1. "... this mechanism is called the greenhouse effect, even though most greenhouses depend primarily on a different mechanism (namely, limiting convective cooling)." 
21. ^ GP 25 Web Book | Chapter 7
22. ^ Wood, R.W. (1909) "Note on the Theory of the Greenhouse," Philosophical Magazine, 17, pp 319–320. For the text of this online, see R. W. Wood: Note on the Theory of the Greenhouse
23. ^ * Piexoto, JP and Oort, AH: Physics of Climate, American Institute of Physics, 1992. Quote: "...the name water vapor-greenhouse effect is actually a misnomer since heating in the usual greenhouse is due to the reduction of convection"
24. ^ ATM S 211 - Notes
25. ^ Titan: Greenhouse and Anti-greenhouse :: Astrobiology Magazine - earth science - evolution distribution Origin of life universe - life beyond :: Astrobiology is study of earth...
26. ^ SPACE.com - Pluto Colder Than Expected
27. ^ Kasting, James F. (1991). "Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus.". Planetary Sciences: American and Soviet Research/Proceedings from the U.S.-U.S.S.R. Workshop on Planetary Sciences. Commission on Engineering and Technical Systems (CETS). pp. 234-245. 
28. ^ Rasool, I.; De Bergh, C. (Jun 1970). "The Runaway Greenhouse and the Accumulation of CO2 in the Venus Atmosphere". Nature 226 (5250): 1037. doi:10.1038/2261037a0. ISSN 0028-0836. PMID 16057644. http://pubs.giss.nasa.gov/docs/1970/1970_Rasool_DeBergh.pdf. Retrieved 02/25/2009.  edit

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