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Greenhouse effect is when the earth become hotter and therefore we die,
{{Cleanup|date=August 2008}}
[[File:The green house effect.svg|thumb|400px|right|Simple diagram of greenhouse effect]]
{{seealso|Global warming}} for a discussion of current [[climate change]] due to human activity.
The '''greenhouse effect''' refers to the change in the [[steady state]] temperature of a planet or moon by the presence of an [[atmosphere]] containing gas that absorbs and emits [[infrared|infrared radiation]].<ref>[http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_appendix.pdf] IPCC AR4 SYR Appendix Glossary</ref> [[Greenhouse gases]], which include water vapor, carbon dioxide and methane, warm the atmosphere by efficiently absorbing thermal infrared radiation emitted by the [[Earth| Earth’s]] surface, by the atmosphere itself, and by [[clouds]]. As a result of its warmth, the atmosphere also radiates thermal infrared in all directions, including downward to the Earth’s surface. Thus, greenhouse gases trap heat within the surface-troposphere system.<ref name="ipcc-AR4WG1">A concise description of the greenhouse effect is given in the ''Intergovernmental Panel on Climate Change Fourth Assessment Report,'' "What is the Greenhouse Effect?" [http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch01.pdf 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."</ref><ref>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.</ref><ref>E. Claussen, V. A. Cochran, and D. P. Davis, ''Climate Change: Science, Strategies, & Solutions,'' University of Michigan, 2001. p. 373.</ref><ref>A. Allaby and M. Allaby, ''A Dictionary of Earth Sciences,'' Oxford University Press, 1999, ISBN 0192800795, p. 244.</ref> This mechanism is fundamentally different from the mechanism of an actual [[Solar greenhouse (technical)|greenhouse]], which instead isolates air inside the structure so that the heat is not lost by [[convection]] and [[Heat conduction|conduction]], as discussed below. The greenhouse effect was discovered by [[Joseph Fourier]] in 1824, first reliably experimented on by [[John Tyndall]] in the year 1858 and first reported quantitatively by [[Svante Arrhenius]] in his 1896 paper.<ref>[http://arjournals.annualreviews.org/doi/full/10.1146/annurev.energy.25.1.441 Annual Reviews (requires registration)]</ref>

In the absence of the greenhouse effect and an atmosphere, the [[Earth|Earth's]] average surface temperature<ref>The elusive "absolute surface air temperature," see [http://data.giss.nasa.gov/gistemp/abs_temp.html GISS discussion]</ref> of 14 °C (57 °F) could be as low as −18&nbsp;°C (−0.4 °F), the [[black body]] temperature of the Earth.<ref name= "IPCC4_ch01">[http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_Ch01.pdf Intergovernmental Panel on Climate Change Fourth Assessment Report. Chapter 1: Historical overview of climate change science] page 97</ref><ref>http://www.ldeo.columbia.edu/edu/dees/V1003/lectures/solar_radiation/</ref><ref>http://eesc.columbia.edu/courses/ees/climate/lectures/radiation/</ref>

[[Anthropogenic]] [[global warming]] (AGW), a recent warming of the Earth's lower atmosphere as evidenced by the global mean temperature anomaly trend,<ref>[http://www.ncdc.noaa.gov/gcag/gcagmerged.jsp Merged land air and sea surface temperature data set]</ref> is believed to be the result of an "enhanced greenhouse effect" mainly due to human-produced increased concentrations of [[greenhouse gas]]es in the atmosphere<ref>[http://www.science.org.au/nova/016/016key.htm The enhanced greenhouse effect]</ref> and changes in the [[Land use, land-use change and forestry|use of land]].<ref>[http://www.grida.no/climate/ipcc/land_use/003.htm Land Use, Land-Use change and Forestry, IPCC Special report SPM]</ref>

The greenhouse effect is one of several factors that affect the temperature of the Earth. [[Earth's energy budget|Other positive and negative feedbacks]] dampen or amplify the greenhouse effect.

In our solar system, [[Mars]], [[Venus]], and the moon [[Titan (moon)|Titan]] also exhibit greenhouse effects according to their respective environments. In addition, Titan has an [[anti-greenhouse effect]] and [[Pluto#Atmosphere|Pluto]] exhibits behavior similar to the anti-greenhouse effect.<ref>http://www.atmos.washington.edu/2002Q4/211/notes_greenhouse.html</ref><ref>http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1762&mode=thread&order=0&thold=0</ref><ref>http://www.space.com/scienceastronomy/060103_pluto_cold.html</ref>

== Basic mechanism ==
{{see also|Radiative forcing}}
[[Image:Greenhouse Effect.svg|thumb|250px|right|A schematic representation of the exchanges of energy between [[outer space]], the [[Earth's atmosphere]], and the Earth 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 Earth receives energy from the Sun mostly in the form of visible light. The bulk of this energy is not absorbed by the atmosphere since the atmosphere is transparent to visible light. 50% of the sun's energy reaches the Earth which is absorbed by the surface as heat. Because of its temperature, the Earth's surface radiates energy in infrared range. The Greenhouse gases are not transparent to infrared radiation so they absorb infrared radiation. Infrared radiation is absorbed from all directions and is passed as heat to all gases in the atmosphere. The atmosphere also radiates in the infrared range (because of its temperature, in the same way the Earth's surface does) and does so in all directions. The surface and lower atmosphere are warmed because of the greenhouse gases and makes our life on earth possible.<ref name= "IPCC4_ch01" />

===Detailed explanation===
[[Image:Solar Spectrum.png|thumb|350px|right|[[Solar radiation]] at top of atmosphere and at Earth's surface.]]

[[Image:Atmospheric Transmission.png|thumb|350px|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 [[Solar radiation|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 [[albedo|reflects]] about 30% of the incoming solar radiation. The remaining 70% is absorbed, warming the land, atmosphere and ocean.

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 [[Stefan-Boltzmann Law|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 light|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 infrared photons emitted by the surface are mostly absorbed in the atmosphere by greenhouse gases and clouds and do not escape directly to space.

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 photons are emitted into space. If the atmosphere is more opaque, the typical photon escaping to space will be emitted from higher in the atmosphere, because one then has to go to higher altitudes to ''see'' out to space in the infrared. Since the emission of infrared radiation is a function of temperature, it is the temperature of the atmosphere at this emission 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&ndash;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 model]]ing literature.

== Greenhouse gases ==
{{main|Greenhouse gas}}

[[Quantum mechanics]] provides the basis for computing the interactions between [[molecule]]s and radiation. Most of this interaction occurs when the [[frequency]] of the radiation closely matches that of the [[spectral line]]s of the molecule, determined by the quantization of the modes of vibration and rotation of the molecule. (The electronic excitations are generally not relevant for infrared radiation, as they require energy larger than that in an infrared photon.)

[[Image:Global Carbon Emission by Type to Y2004.png|thumb|left|250px|Modern global anthropogenic [[Carbon]] emissions.]]

[[Image:Major greenhouse gas trends.png|thumb|left|350px|Major greenhouse gas trends]]

The width of a spectral line is an important element in understanding its importance for the absorption of radiation. In the Earth’s atmosphere these spectral widths are primarily determined by “pressure broadening”, which is the distortion of the spectrum due to the collision with another molecule. Most of the infrared absorption in the atmosphere can be thought of as occurring while two molecules are colliding. The absorption due to a photon interacting with a lone molecule is relatively small. This three-body aspect of the problem, one photon and two molecules, makes direct quantum mechanical computation for molecules of interest more challenging. Careful laboratory [[Spectroscopy|spectroscopic measurements]], rather than ''ab initio'' quantum mechanical computations, provide the basis for most of the radiative transfer calculations used in studies of the atmosphere.

[[Image:CO2 increase rate.png|thumb|left|Year-over-year increase of atmospheric CO<sub>2</sub>: In the 1960s, the average annual increase was 37% of what it was in 2000 through 2007.<ref>Dr. Pieter Tans (May 3, 2008) [ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_gr_mlo.txt "Annual CO2 mole fraction increase (ppm)" for 1959-2007] [[National Oceanic and Atmospheric Administration]] Earth System Research Laboratory, Global Monitoring Division ([http://www.esrl.noaa.gov/gmd/ccgg/trends/ additional details].)</ref>]]

The molecules/atoms that constitute the bulk of the atmosphere: [[oxygen]] (O<sub>2</sub>), [[nitrogen]] (N<sub>2</sub>) and [[argon]] (Ar); do not interact with infrared radiation significantly. While the oxygen and nitrogen molecules can vibrate, because of their symmetry these vibrations do not create any transient charge separation. Without such a transient [[dipole]] moment, they can neither absorb nor emit infrared radiation. In the Earth’s atmosphere, the dominant infrared absorbing gases are [[water vapor]], [[carbon dioxide]], and [[ozone]] (O<sub>3</sub>). The same molecules are also the dominant infrared emitting molecules. CO<sub>2</sub> and O<sub>3</sub> have "floppy" vibration motions whose quantum states can be excited by collisions at energies encountered in the atmosphere. For example, carbon dioxide is a linear molecule, but it has an important vibrational mode in which the molecule bends with the carbon in the middle moving one way and the oxygens on the ends moving the other way, creating some charge separation, a [[dipole moment]], thus carbon dioxide molecules can absorb IR radiation. Collisions will immediately transfer this energy to heating the surrounding gas. On the other hand, other CO<sub>2</sub> molecules will be vibrationally excited by collisions. Roughly 5% of CO<sub>2</sub> molecules are vibrationally excited at room temperature and it is this 5% that radiates. A substantial part of the greenhouse effect due to carbon dioxide exists because this vibration is easily excited by infrared radiation. CO<sub>2</sub> has two other vibrational modes. The symmetric stretch does not radiate, and the asymmetric stretch is at too high a frequency to be effectively excited by atmospheric temperature collisions, although it does contribute to absorption of IR radiation. The vibrational modes of water are at too high energies to effectively radiate, but do absorb higher frequency IR radiation. Water vapor has a bent shape. It has a permanent dipole moment (the O atom end is electron rich, and the H atoms electron poor) which means that IR radiation can be emitted and absorbed during rotational transitions, and these transitions can also be produced by collisional energy transfer. Clouds are also very important infrared absorbers. Therefore, water has multiple effects on infrared radiation, through its vapor phase and through its condensed phases. Other absorbers of significance include [[methane]], [[nitrous oxide]] and the [[chlorofluorocarbon]]s.

Discussion of the relative importance of different infrared absorbers is confused by the overlap between the spectral lines due to different gases, widened by pressure broadening. As a result, the absorption due to one gas cannot be thought of as independent of the presence of other gases. One convenient approach is to remove the chosen constituent, leaving all other absorbers, and the temperatures, untouched, and monitoring the infrared radiation escaping to space. The reduction in infrared absorption is then a measure of the importance of that constituent. More precisely, define the greenhouse effect (GE) to be the difference between the infrared radiation that the surface would radiate to space if there were no atmosphere and the actual infrared radiation escaping to space. Then compute the percentage reduction in GE when a constituent is removed. The table below is computed by this method, using a particular 1-dimensional model of the atmosphere. More recent 3D computations lead to similar results.

<center>

{| class="wikitable" style="text-align:center"
!Gas removed

! percent reduction in GE
|-
| H<sub>2</sub>O || 36%
|-
| CO<sub>2</sub> || 9%
|-
| O<sub>3</sub> || 3%
|}

(Source: GISS-GCM ModelE simulation) <ref>RealClimate, [http://www.realclimate.org/index.php?p=142 ''Water vapour: feedback or forcing?'']</ref>

</center>

By this particular measure, water vapor can be thought of as providing 36% of the greenhouse effect, and carbon dioxide 9%, but the effect of removal of both of these constituents will be greater than the total that each reduces the effect, in this case, around 45%. An additional proviso is that these numbers are computed holding the cloud distribution fixed. But removing water vapor from the atmosphere while holding clouds fixed is not likely to be physically relevant. In addition, the effects of a given gas are typically nonlinear in the amount of that gas, since the absorption by the gas at one level in the atmosphere can remove photons that would otherwise interact with the gas at another altitude. The kinds of estimates presented in the table, while often encountered in the controversies surrounding global warming, must be treated with caution. Different estimates found in different sources typically result from different definitions and do not reflect uncertainties in the underlying radiative transfer.

== Positive feedback and runaway greenhouse effect==
{{main|Runaway climate change}}
When there is a loop of effects such as the concentration of a greenhouse gas itself being a function of temperature, there is a [[positive feedback|feedback]]. If the effect is to act in the same direction on temperature it is a [[positive feedback]]; and if in the opposite direction it is a [[negative feedback]]. Feedback effects can be on the same cause as the forcing, via another greenhouse gas, or on other effects such as change in ice cover affecting the planet's [[albedo]].<ref>Physics of the Greenhouse Effect (March 10, 2008) http://chriscolose.wordpress.com/2008/03/10/physics-of-the-greenhouse-effect-pt-2/</ref>

Positive feedbacks do not have to lead to a runaway effect. With radiation from the Earth increasing in proportion to the fourth power of temperature, in accordance with the [[Stefan-Boltzmann law]], the feedback effect has to be very strong to cause a runaway effect. An increase in temperature from greenhouse gases leading to increased water vapor which is a greenhouse gas causing further warming is a positive feedback. This cannot be a runaway effect or the runaway effect would have occurred long ago. Positive feedback effects are common and can always exist while runaway effects are much rarer and cannot be operating at all times.

If the effects from the second iteration of the loop of effects is larger than the effects of the first iteration of the loop this will lead to a self perpetuating effect. If this occurs and the feedback only ends after producing a major temperature increase, it is called a '''runaway greenhouse effect'''. A runaway feedback could also occur in the opposite direction leading to an ice age. Runaway feedbacks are bound to stop, since infinite temperatures are not observed. They are stopped by factors like a reducing supply of a greenhouse gas or a phase change of the gas or ice cover reducing towards zero or increasing toward a large size that is difficult to increase.

A runaway greenhouse effect involving CO<sub>2</sub> and water vapor may have occurred on [[Venus]].<ref>S. I. Rasoonl and C. de Bergh, "The Runaway Greenhouse Effect and the Accumulation of CO2 in the Atmosphere of Venus," ''Nature,'' 226', pp. 1037-1039, 1970.</ref> In this scenario, early Venus may have had a global ocean. As the brightness of the early sun increased, the amount of water vapor in the atmosphere increased, increasing the temperature and consequently increasing the evaporation of the ocean, leading eventually to the situation in which the oceans boiled, and all of the water vapor entered the atmosphere. On Venus today there is little water vapor in the atmosphere. If water vapor did contribute to the warmth of Venus at one time, this water is thought to have escaped to space. Venus is sufficiently strongly heated by the Sun that water vapor can rise much higher in the atmosphere and be split into [[hydrogen]] and [[oxygen]] by ultraviolet light. The hydrogen can then escape from the atmosphere and the oxygen recombines. Carbon dioxide, the dominant greenhouse gas in the current Venusian atmosphere, likely owes its larger concentration to the weakness of carbon recycling as compared to Earth, where the carbon dioxide emitted from volcanoes is efficiently [[Subduction|subducted]] into the Earth by plate tectonics on geologic time scales.<ref>[http://home.case.edu/~sjr16/venus.html Venus - Stuart Robbins and David McDonald]</ref><ref>Notes (created by Nick Strobel) for an introductory astronomy courses he teaches.
*[http://www.astronomynotes.com/solarsys/s9.htm Nick's new site]
*[http://web.archive.org/web/20070324205501/http://astronomy.nju.edu.cn/astron/Astronomynotes/solsysb.htm Old site (The Wayback Machine)]</ref>

According to the [[clathrate gun hypothesis]] a runaway greenhouse effect could be caused by liberation of methane gas from hydrates by global warming if there are sufficient hydrates close to unstable conditions. It has been speculated that the [[Permian-Triassic extinction event]]<ref>How to kill (almost) all life: the end-Permian extinction event, Michael J. Benton and Richard J. Twitchett, Department of Earth Sciences University of Bristol UK, TRENDS in Ecology and Evolution Vol.18 No.7 July 2003, {{DOI|10.1016/S0169-5347(03)00093-4}} ({{PDFlink|[http://palaeo.gly.bris.ac.uk/Benton/reprints/2003TREEPTr.pdf full reprint]|506&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 518857 bytes -->}})</ref> was caused by such a runaway effect. It is also thought that large quantities of methane could be released from the Siberian tundra as it begins to thaw, methane being 21 times more potent a greenhouse gas than carbon dioxide.<ref>[http://environment.newscientist.com/channel/earth/mg19125713.300-climate-change-one-degree-and-were-done-for.html Climate change: 'One degree and we're done for' - earth - September 27, 2006 - New Scientist Environment<!-- Bot generated title -->]</ref>

== Anthropogenic greenhouse effect ==
{{main|Global warming}}

Of the human-produced greenhouse gases, the one that contributes the bulk in terms of [[radiative forcing]] is [[carbon dioxide]]. CO<sub>2</sub> production from increased industrial activity (fossil fuel burning) and other human activities such as cement production and tropical deforestation<ref name="IPCC deforestation">IPCC [http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter7.pdf Fourth Assessment Report, Working Group I Report "The Physical Science Basis"] Chapter 7</ref> has increased the concentrations in the atmosphere. Measurements of CO<sub>2</sub> from the Mauna Loa observatory show that concentrations have increased from about 313 ppm (mole fraction in dry air<ref>{{cite web| url=http://www.esrl.noaa.gov/gmd/ccgg/trends/co2_data_mlo.html | title=Atmospheric Carbon Dioxide - Mauna Loa | publisher=[[NOAA]] }}</ref>) in 1960 to about 375 ppm in 2005. The current observed amount of CO<sub>2</sub> exceeds the geological record maxima (~300 ppm) from ice core data.<ref>Hansen, J., Climatic Change, '''68''', 269, 2005 [http://www.springerlink.com/content/x283l27781675v51/?p=799ebc88193f4ecfa8ca76f6e28f45d7 ISSN 0165-0009]</ref>

The effect of combustion-produced carbon dioxide on the global climate, a special case of the greenhouse effect first demonstrated in the 1930s, may be called the [[Callendar effect]].

Because it is a greenhouse gas, elevated CO<sub>2</sub> 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''".<ref>IPCC Fourth Assessment Report [http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf Synthesis Report: Summary for Policymakers] (p. 5)</ref>

Over the past 800,000 years,<ref>[http://news.bbc.co.uk/2/hi/science/nature/5314592.stm BBC NEWS | Science/Nature | Deep ice tells long climate story<!-- Bot generated title -->]</ref> [[Carbon dioxide#Variation in the past|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.<ref>[http://pubs.acs.org/cen/news/83/i48/8348notw1.html Chemical & Engineering News: Latest News - Ice Core Record Extended<!-- Bot generated title -->]</ref> Certain [[paleoclimatologists]] consider variations in carbon dioxide to be a fundamental factor in controlling climate variations over this time scale.<ref name="Bowen (2005), Thin Ice">Bowen, Mark; Thin Ice: Unlocking the Secrets of Climate in the World's Highest Mountains; Owl Books, 2005.</ref>

The amount of [[global warming]] caused by [[CO2]] emissions can be modified by [[feedback]]s and and [[climate tipping points]]. It is thought by some scientists that the existing [[greenhouse effect]] is sufficient to induce [[catastrophic climate change]].{{Fact|date=January 2009}}

Responses to anthropogenic global warming fall into three categories:
* [[Adaptation to global warming|Adaptation]] - dealing with the [[effects of global warming]], such as by building [[flood defences]]
* [[Mitigation of global warming|Mitigation]] - reducing [[carbon emissions]], such as by using [[renewable energy]] and [[energy efficiency]] measures.
* [[Geoengineering]] - directly intervening in the climate using techniques such as [[solar radiation management]]

== Real greenhouses ==

{{main|Solar greenhouse (technical)}}

[[Image:RHSGlasshouse.JPG|thumb|right|250px|A modern [[Greenhouse]] in [[Wisley Garden|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<ref>[http://www.epa.gov/globalwarming/kids/greenhouse.html EPA Climate Change Site]</ref>.

The term 'greenhouse effect' originally came from the greenhouses used for gardening, but as mentioned the mechanism for greenhouses operates differently.<ref name="Schroeder">
{{Cite book
| author=Schroeder, Daniel V.
| title=An introduction to thermal physics
| year=2000
| publisher=[[Addison-Wesley]]
| location=[[San Francisco, California]]
| isbn=0-321-27779-1
| quote=... this mechanism is called the ''greenhouse effect'', even though most greenhouses depend primarily on a different mechanism (namely, limiting convective cooling).
| pages=305–307}}
</ref> 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.<ref> [http://pangea.stanford.edu/courses/gp025/webbook/07_clement.html GP 25 Web Book | Chapter 7<!-- Bot generated title -->]</ref> <!-- NOAA paleoclimate link deleted because it didn't seem relevant to real greenhouse section here http://www.ncdc.noaa.gov/paleo/globalwarming/what.html#greenhouse NOAA Paleoclimatology Global Warming - The Story-->

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.<ref name= "wood1909">Wood, R.W. (1909) "Note on the Theory of the Greenhouse," ''Philosophical Magazine, 17'', pp 319–320. For the text of this online, see [http://www.wmconnolley.org.uk/sci/wood_rw.1909.html R. W. Wood: Note on the Theory of the Greenhouse]</ref> <!-- "When exposed to sunlight the temperature rose gradually to 65 C., the enclosure covered with the salt plate keeping a little ahead of the other, owing to the fact that it transmitted the longer waves from the sun, which were stopped by the glass. In order to eliminate this action the sunlight was first passed through a glass plate." "it is clear that the rock-salt plate is capable of transmitting practically all of it, while the glass plate stops it entirely. This shows us that the loss of temperature of the ground by radiation is very small in comparison to the loss by convection, in other words that we gain very little from the circumstance that the radiation is trapped." --> Greenhouses thus work primarily by preventing ''[[convection]]''; the atmospheric greenhouse effect however reduces ''radiation loss'', not convection.<ref>* 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"</ref><ref name="Schroeder" />

== See also ==
{{wikibooks|Climate Change}}
{{wikiversity|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]]

== Footnotes ==
<references />

== 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 CO<sub>2</sub> 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.

{{global warming}}

[[Category:Atmospheric radiation]]
[[Category:Climate change feedbacks and causes]]
[[Category:Climate forcing]]
[[Category:Atmosphere]]

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[[lt:Šiltnamio efektas]]
[[hu:Üvegházhatás]]
[[ml:ഹരിതഗൃഹ പ്രഭാവം]]
[[mr:हरितगृह परिणाम]]
[[ms:Kesan rumah hijau]]
[[nl:Broeikaseffect]]
[[ja:温室効果]]
[[no:Drivhuseffekt]]
[[nn:Drivhuseffekt]]
[[oc:Efièch de sèrra]]
[[pl:Efekt cieplarniany]]
[[pt:Efeito estufa]]
[[ro:Efect de seră]]
[[qu:Pacha q'uñichiy]]
[[ru:Парниковый эффект]]
[[si:හරිතාගාර ආචරණය]]
[[simple:Greenhouse effect]]
[[sk:Skleníkový efekt]]
[[sl:Učinek tople grede]]
[[sr:Efekat staklene bašte]]
[[fi:Kasvihuoneilmiö]]
[[sv:Växthuseffekten]]
[[ta:பைங்குடில் விளைவு]]
[[th:ปรากฏการณ์เรือนกระจก]]
[[vi:Hiệu ứng nhà kính]]
[[tr:Sera etkisi]]
[[uk:Парниковий ефект]]
[[wuu:温室效应]]
[[zh-yue:溫室效應]]
[[zh:温室效应]]

Revision as of 12:18, 6 February 2009

Greenhouse effect is when the earth become hotter and therefore we die,

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