A Summary and Explanation of the Greenhouse Effect Phenomenon - Report Example

The greenhouse effect is a thermal process by which solar radiation from a star is trapped upon a planetary surface in the form of heat, and then absorbed by atmospheric greenhouse gases. The actual heat energy is again radiated outwardly. Since a portion of this re-released heat radiation returns to the planets surface, energy is then transferred to the surface and the lower reaches of the atmosphere. consequently, the temperature becomes higher than it would be from the direct consequences of actual heating only by solar radiation as a warming mechanism. (Claussen, 2001) The origin of the term, giving reference to botanical greenhouses pays homage to a simpler, localized means of restricting heat-flow. The transparent surface of the botanical greenhouse permits heat from radiation to warm the plant-nurturing interior, and that heat is concentrated due to the physical enclosure that restricts aerial convection. The restraint of normal convection in this instance, creates the localized temperature increase. The exact consequences and risk factors from the Greenhouse effect is terms of long-term climate effects as provoked vociferous scientific debate, as it may pertain to changes caused by human activity. The famed physicist Svante Arrhenius once calculated that doubling the Earths natural carbon dioxide Greenhouse effect, such as caused by the combustion of fossil fuels, would generate a surface temperature increase on average of 5.2 °C. His calculations indicated that an increase equal to half of these levels could raise the temperature 3.0 °C.2. (Arrhenius, 1896) The Greenhouse effect has, in other places been attributed to a warming effect that allegedly generates a higher probability of hurricanes. In March 1996, Eileen Claussen gave lecture at a “Town Meeting on Global Warming” in Chapel Hill, North Carolina, the substance of which being that the then recent Hurricane Fran (1996) " .. was typical of what one could expect from global warming." Based in part on a 1987 paper, (Emanuel, 1987.) In essence, the Greenhouse effect depends upon Greenhouse gases, typically carbon dioxide - but also methane, water vapor and nitrous oxide. (Robertson et al. 2000) Actually, water vapor itself is the most thermally important gas in terms of heat-capture in the troposphere; with carbon dioxide a close second. Some dispute exists as to whether and which gas has the most impact, while general agreement exists that water vapor is the strongest greenhouse gas in terms of heat-capture, and temperature contribution, estimates vary as to the exact percentages of heat increase either gas is responsible for. Figures range from 70 percent - (Kiehl & Trenberth, 1997) to 95% - (Michaels, 1998) This leaves room for speculation concerning the magnitude of the role of carbon dioxide; but there is little doubt that it does cause greenhouse warming, and is the second largest contributor to this form of heat-capture. To clarify, water vapors effect is illustrated from heat losses in the upper atmosphere, which is known to accelerate due to the lower concentrations of water vapor at higher elevations. (13) A concentration of these gases in a planetary atmosphere creates a layer in which radiating energy from the sun is allowed to pass relatively unimpeded. The radiation incoming from the Sun largely takes the form of visible light and nearby wavelengths, usually in the range 0.2–4 µm, which is the natural byproduct of a body with our Suns radiative temperature of 6,000 K. (Mitchell, 1989) But the resulting heat-energy that results when radiant light contacts solid matter is retained. A one-way energy-mirror arises; allowing light to pass but not heat. This heat therefore, accumulates in the atmosphere beneath these Greenhouse gas- layers, which allows a larger increase in temperature than would otherwise be possible. The exact effect varies with atmospheric pressure and quantities of the effector-gases. The easiest, starkest demonstration of the power of the Greenhouse effect is the obvious one of other inner-planets in our Solar System. Mercury for instance, shifts wildly in temperature; the heat it receives bleeding off easily and immediately into space, the far side from the sun being sub-zero, but the near side heating to over 700 kelvin, with no atmosphere; given nothing to hold the heat, such shifts are inevitable with celestial objects. Except those with measurable atmospheric pressure. Venus, for instance. Where Mercury is an object lesson on the perils and pitfalls of an environment with no atmosphere; and the corresponding lack of a Greenhouse effect; Venus is the classic poster-child of Greenhouse- gone-wild. A layperson might be forgiven for believing that Mercury would claim first prize as the hottest of Sols planetary children. But it is not. Even though Mercury is far closer, Venus is still hotter. A lead-melting 735 Kelvin (460 C) is the normal temperature on the surface of Earths smoking-hot sister. (Coffey, 2008) Such is the power of the Greenhouse effect. The culprit in Venus case being the the aforementioned hothouse molecule Carbon Dioxide, but at far greater levels. And this is not limited to just one side of Venus; scorching winds spread the wealth from pole to pole, with only the faintest traces of heat energy escaping to space. Almost half the relevant solar radiation that initially triggers warming is in the form of "visible" light, naturally suited for our eyes, or rather the form our eyes have become suited to use. Within this radiative cornucopia, approximately half of the Suns energy is absorbed by the surface of the Earth, as the remainder is absorbed or reflected by the ambient atmosphere. Some light is inevitably reflected back into space, usually by clouds, and does not factor into the heat-absorption calculations of energy emanating from the surface. This light is lost to the system. It is The absorbed heat-energy that warms the surface of the planet. Simple exhibitions of the greenhouse effect, show surface heat being lost in the form of thermal radiation. In reality, air near the surface becomes much less permeable to thermal radiation, with some exceptions, and most surface heat loss is due to localized mechanisms of heat transfer. as mentioned above, Radiative heat-energy losses are more impactful in higher atmospheric layers essentially due to decreased levels of water vapor. The most affected layer is actually the mid-troposphere in terms of temperature increase due to radiant heat. There exists interplay between these layers and the surface through a specific a lapse rate. In the region where radiative effects have their greatest effect the description given by the standard theory of the greenhouse effect conforms to expectations: The surface of the Earth, heated heated on the order of 255 K, will then radiate long-wavelength infrared heat- energy, usually close to 4–100 µm. (Mitchell, 1989) These wavelengths result in greenhouse gases that allow incoming radiation to pass unimpeded for the most part. (Mitchell, 1989) Every layer of atmosphere possessing greenhouses gases absorbs a quantity of the heat radiated up from lower layers. Most gases, including Greenhouse gases do possess a property that allows them to radiate in the infrared in proportion to a given temperature. A particular atmospheric layer achieves stability by radiating the heat it does absorb both upwards and downwards. This transfers more warmth below the layer, accumulating at ground level, yet nonetheless radiating enough heat back to outer space from the upper atmospheric layers in order to maintain overall stability of temperature. Natural sources of atmospheric carbon dioxide can in some cases include volcanic activity, and slow diffusion from natural oil deposits left by ancient life. Normal respiration by living animals also contributes CO² into the carbon cycle, where it is typically incorporated into plant respiration to release oxygen. (EPA.gov 2011) Atmospheric concentrations of carbon dioxide can be enhanced by human industry. Sources of what is termed anthropogenic carbon dioxide can accumulate to levels that can yield thermal consequences for the atmosphere and climate. While some dissenters do exist, many governments, and intergovernmental panels agree with the assessment that carbon dioxide from man-made sources adds to absorption and thus emission of thermal infrared energy into the atmosphere, which is projected to yield measurable temperature increases. The latest assessment of the Intergovernmental panel on Climate change has concluded: "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". (IPCC 2007) In summary; the Greenhouse effect is the result of solar radiation penetrating the atmosphere of a planetary surface where it is absorbed in part by the surface, and by tropospheric layers of gases. The combination of subsequent infrared radiation from heated air and land masses raises the temperature. Gases, primarily water vapor trap this radiant heat, even as they allow solar rays to pass unimpeded; this generates a reliably warmer climate than would otherwise exist solely from direct solar heating. Planets such as Mercury demonstrate the radical temperature swings that exist without Greenhouse warming, and Venus illustrates an infernal extreme that the Greenhouse effect can cause. Carbon dioxide is the second strongest effector, in heat-trapping for the troposphere, but estimates vary concerning its interplay with water vapor in terms of overall influence in heat-capture. The levels of carbon dioxide, among greenhouse gases are most likely to be effected by human industry, agriculture, and transportation. Most agencies agree that a warming trend will result from anthropogenic contributions of CO² to the Earths carbon cycle. The possibility of polar ice-cap melting, the destruction of habitats – especially in arctic regions, and consequences for agriculture are potent considerations that must be carefully weighed by policy-makers, captains of industry, and the voting public. With countless billions of dollars at stake, it behooves all children of the planet to sift science from hyperbole and analyze the facts of climate change and the Greenhouse effect. REFERENCES Arrhenius, Svante “On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground,” Philisophical Magazine 41 (1896), pp. 237–276. Coffey, Jerry 2008. Universetoday.com, MAy 15th, 2008. http://www.universetoday.com/14306/temperature-of-venus/ Claussen, E. Cochran, V.A. Davis, D.P. 2001. Climate Change: Science, Strategies, & Solutions, University of Michigan, 2001. Emanuel, K.A. 1987. “On the Maximum Intensity of Hurricanes,” Journal of the Atmospheric Sciences, 45 (1987), pp. 1143–1156. Intergovernmental Panel on Climate Change. 2007. Climate Change 2007: Synthesis Report. A Summary for Policymakers. An Assessment of the Intergovernmental Panel on Climate Change. Kiehl, J. T., Trenberth, K. E. 1997. "Earths Annual Global Mean Energy Budget" (PDF). Bulletin of the American Meteorological Society 78 (2): 197–208. Michaels, Patrick J. 1998. Global Deception: The Exaggeration of the Global Warming Threat. Center for the Study of American Business. Policy Study Number 146, June 1998. Mitchell, John F. B. (1989). "THE "GREENHOUSE" EFFECT AND CLIMATE CHANGE". Reviews of geophysics (American Geophysical Union) 27 (1): 115–139. Robertson, Phillip G. Eldor, Paul A. Harwood, Richard R. 2000. Greenhouse Gases in Intensive Agriculture: Contribution of Individual Gases to the radiative forcing of the atmosphere. Science Mag. United States Environmental Protection Agency. 2011. Climate Change: Greenhouse Gas Emissions. Natural Sources and Sinks of Carbon Dioxide. http://www.epa.gov/climatechange/emissions/co2_natural.html, Last updated on Thursday, April 14, 2011, Accessed 10/22/2011 Read More