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greenhouse effect

 
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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.
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n.
  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.

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Sci-Tech Encyclopedia: Greenhouse effect
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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.

 
Geography Dictionary: greenhouse effect
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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.

 
Britannica Concise Encyclopedia: greenhouse effect
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Some incoming sunlight is reflected by the Earth's atmosphere and surface, but most is absorbed by …
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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.

 
Science Q&A: What is the greenhouse effect?
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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.

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Science Dictionary: greenhouse effect
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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.

  • The burning of fossil fuels adds carbon dioxide to the atmosphere, and therefore places the Earth at risk from an increase of this effect.

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    Wikipedia: Greenhouse effect
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    		 This article may require cleanup to meet Wikipedia's quality standards. Please improve this article if you can. (August 2008)
    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] Greenhouse gases are almost transparent to solar radiation but strongly absorb and emit infrared radiation. Thus, greenhouse gases trap heat within the surface-troposphere system.[2][3][4][5] 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.[6]

    In the absence of the greenhouse effect and an atmosphere, the Earth's average surface temperature[7] of 14 °C (57 °F) could be as low as −18 °C (−0.4 °F), the black body temperature of the Earth.[8][9][10] Anthropogenic global warming (AGW), a recent warming of the Earth's lower atmosphere as evidenced by the global mean temperature anomaly trend,[11] is believed to be the result of an "enhanced greenhouse effect" mainly due to human-produced increases in atmospheric greenhouse gases.[12]

    Contents

    Basic mechanism

    See also: Radiative forcing

    The Earth receives energy from the Sun mostly in the form of visible light. The atmosphere is almost transparent to visible light, so that about 50% of the sun's energy reaches the Earth and is absorbed by the surface. Like all bodies with a temperature above absolute zero the Earth's surface radiates energy in the infrared range. Greenhouse gases absorb infrared radiation 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.[8]

    Detailed explanation

    Pattern of absorption bands generated by various greenhouse gases and their impact on both solar radiation and upgoing thermal radiation from the Earth's surface. Note that a greater quantity of upgoing radiation is absorbed, which contributes to the greenhouse effect.

    The Earth receives energy from the Sun in the form of radiation. Most of the energy is in visible wavelengths and in infrared wavelengths that are near the visible range (often called "near infrared"). The Earth reflects about 30% of the incoming solar radiation. The remaining 70% is absorbed by the land, atmosphere and ocean and warms them.

    For the Earth's temperature to be in steady state so that the Earth does not rapidly heat or cool, this absorbed solar radiation must be very closely balanced by energy radiated back to space in the infrared wavelengths. Since the intensity of infrared radiation increases with increasing temperature, one can think of the Earth's temperature as being determined by the infrared flux needed to balance the absorbed solar flux. The visible solar radiation mostly heats the surface, not the atmosphere, whereas most of the infrared radiation escaping to space is emitted from the upper atmosphere, not the surface.

    The reason this warms the surface is most easily understood by starting with a simplified model of a purely radiative greenhouse effect that ignores energy transfer in the atmosphere by convection (sensible heat transport, Sensible heat flux) and by the evaporation and condensation of water vapor (latent heat transport, Latent heat flux). In this purely radiative case, one can think of the atmosphere as emitting infrared radiation both upwards and downwards. The upward infrared flux emitted by the surface must balance not only the absorbed solar flux but also this downward infrared flux emitted by the atmosphere. The surface temperature will rise until it generates thermal radiation equivalent to the sum of the incoming solar and infrared radiation.

    A more realistic picture taking into account the convective and latent heat fluxes is somewhat more complex. But the following simple model captures the essence. The starting point is to note that the opacity of the atmosphere to infrared radiation determines the height in the atmosphere from which most of the energy is emitted into space. If the atmosphere is more opaque then the radiant energy escaping to space will be emitted from a higher altitude, because one then has to go to higher altitudes to see out to space in the infrared. Since the emission of infrared radiation increases strongly with increasing temperature, it is the temperature of the atmosphere at this level that is effectively determined by the requirement that the emitted flux balance the absorbed solar flux.

    But the temperature of the atmosphere generally decreases with height above the surface, at a rate of roughly 6.5 °C per kilometer on average, until one reaches the stratosphere 10–15 km above the surface. (Most infrared photons escaping to space are emitted by the troposphere, the region bounded by the surface and the stratosphere, so we can ignore the stratosphere in this simple picture.) A very simple model, but one that proves to be remarkably useful, involves the assumption that this temperature profile is simply fixed, by the non-radiative energy fluxes. Given the temperature at the emission level of the infrared flux escaping to space, one then computes the surface temperature by increasing temperature at the rate of 6.5 °C per kilometer, the environmental lapse rate, until one reaches the surface. The more opaque the atmosphere, and the higher the emission level of the escaping infrared radiation, the warmer the surface, since one then needs to follow this lapse rate over a larger distance in the vertical. While less intuitive than the purely radiative greenhouse effect, this less familiar radiative-convective picture is the starting point for most discussions of the greenhouse effect in the climate modeling literature.

    Greenhouse gases

    Main article: Greenhouse gas

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

    When these gases are ranked by their contribution to the greenhouse effect, the most important are:

    • 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 greenhouse gases.[13][14]


    Anthropogenic greenhouse effect

    Main article: Global warming

    Carbon dioxide is the human-produced greenhouse gases 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.[15] Measurements of CO2 from the Mauna Loa observatory show that concentrations have increased from about 313 ppm [16] 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.[17] 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".[18]

    Over the past 800,000 years,[19] 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.[20] Certain paleoclimatologists consider variations in carbon dioxide to be a fundamental factor in controlling climate variations over this time scale.[21]

    Real greenhouses

    Main article: Solar greenhouse (technical)

    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[22].

    The term 'greenhouse effect' originally came from the greenhouses used for gardening, but as mentioned the mechanism for greenhouses operates differently.[23] 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.[24]

    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.[25] Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection.[26][23]

    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.[27][28][29]

    A runaway greenhouse effect occurs if positive feedbacks lead to the evaporation of all greenhouse gases into the atmosphere.[30] A runaway greenhouse effect involving carbon dioxide and water vapor may have occurred on Venus.[31]

    See also

    Sister project Wikibooks has a book on the topic of
    Sister project Wikiversity has learning materials about Topic:Climate change

    Footnotes

    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."
    3. ^ 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.
    4. ^ E. Claussen, V. A. Cochran, and D. P. Davis, Climate Change: Science, Strategies, & Solutions, University of Michigan, 2001. p. 373.
    5. ^ A. Allaby and M. Allaby, A Dictionary of Earth Sciences, Oxford University Press, 1999, ISBN 0192800795, p. 244.
    6. ^ Annual Reviews (requires registration)
    7. ^ The elusive "absolute surface air temperature," see GISS discussion
    8. ^ a b Intergovernmental Panel on Climate Change Fourth Assessment Report. Chapter 1: Historical overview of climate change science page 97
    9. ^ V1003 Science and Society - Solar Radiation
    10. ^ Solar Radiation and the Earth's Energy Balance
    11. ^ Merged land air and sea surface temperature data set
    12. ^ The enhanced greenhouse effect
    13. ^ 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 on 2006-05-01. 
    14. ^ "Water vapour: feedback or forcing?". RealClimate. 6 April 2005. http://www.realclimate.org/index.php?p=142. Retrieved on 2006-05-01. 
    15. ^ IPCC Fourth Assessment Report, Working Group I Report "The Physical Science Basis" Chapter 7
    16. ^ "Atmospheric Carbon Dioxide - Mauna Loa". NOAA. http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_data_mlo.html. 
    17. ^ Hansen, J., Climatic Change, 68, 269, 2005 ISSN 0165-0009
    18. ^ IPCC Fourth Assessment Report Synthesis Report: Summary for Policymakers (p. 5)
    19. ^ BBC NEWS | Science/Nature | Deep ice tells long climate story
    20. ^ Chemical & Engineering News: Latest News - Ice Core Record Extended
    21. ^ Bowen, Mark; Thin Ice: Unlocking the Secrets of Climate in the World's Highest Mountains; Owl Books, 2005.
    22. ^ EPA Climate Change Site
    23. ^ 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)." 
    24. ^ GP 25 Web Book | Chapter 7
    25. ^ 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
    26. ^ * 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"
    27. ^ ATM S 211 - Notes
    28. ^ Titan: Greenhouse and Anti-greenhouse :: Astrobiology Magazine - earth science - evolution distribution Origin of life universe - life beyond :: Astrobiology is study of earth...
    29. ^ SPACE.com - Pluto Colder Than Expected
    30. ^ 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: 234-245, Commission on Engineering and Technical Systems (CETS). Retrieved on 2009. 
    31. ^ Rasool, S. I.; De Bergh, C. (1970). "The Runaway Greenhouse and the Accumulation of CO2 in the Venus Atmosphere". Nature 226: 1037. doi:10.1038/2261037a0. http://pubs.giss.nasa.gov/docs/1970/1970_Rasool_DeBergh.pdf. Retrieved on 02/25/2009.  edit

    References

    • 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.
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