The greenhouse effect is created by the ability of the atmosphere to be selective in its response to radiation .It is transparent to high energy, shortwave radiation , such as form the sun, but partially opaque to the lower energy ,long wave radiation emanating from the earth surface .The green house effect , first discovered y Joseph Fourier in 1824 and first investigated quantitavely by Svante arrhenius in1896, is the process by which an atmosphere warms a planet .The name is form the similar effect which greenhouses utilize in order to facilitate plant growth. The term greenhouse effect refers broadly to the partial trapping by the atmosphere of radiation from the earth surface, ladling to a earth surface temperature that is larger than would be the case without the atmosphere.
The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth’s average temperature would be about 60ºF colder. Because of how they warm our world, these gases are referred to as greenhouse gases.
The greenhouse effect is the process in which the emission of infrared radiation by the atmosphere warms a planet's surface.
The greenhouse effect is important. Without the greenhouse effect, the Earth would not be warm enough for humans to live. But if the greenhouse effect becomes stronger, it could make the Earth warmer than usual. Even a little extra warming may cause problems
for humans, plants, and animals.
The name comes from an incorrect analogy with the warming of air inside a greenhouse compared to the air outside the greenhouse.
The greenhouse effect was discovered by Joseph Fourier in 1824 and first investigated quantitatively by Svante Arrhenius in 1896.
The Earth's average surface temperature of 14 °C (57 °F) would otherwise be about -19 °C (-2.2 °F) in the absence of the greenhouse effect. Global warming, a recent warming of the Earth's lower atmosphere, is believed to be the result of an enhanced greenhouse effect due to increased concentrations of greenhouse gases in the atmosphere.
- to know the processes and limiting factors of green house effect .
- to know the components of green house gases.
- to know the nature of green houses gases.
- to know the effect on global warming
- to know the process of curving green house gas emission.
Solar radiation at top of atmosphere and at Earth's surface.
Pattern of absorption bands generated by various greenhouse gases and their impact on both solar radiation and up going thermal radiation from the Earth's surface. Note that a greater quantity of up going 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, 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 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 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 radioactive greenhouse effect that ignores energy transfer in the atmosphere by convection (sensible heat transport) and by the evaporation and condensation of water vapor (latent heat transport). In this purely radioactive 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 10-15 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-radioactive 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 radioactive greenhouse effect, this less familiar radioactive-convective picture is the starting point for most discussions of the greenhouse effect in the climate modeling literature.
The term "greenhouse effect" is a source of confusion in that actual greenhouses do not warm by this mechanism (see section Real greenhouses). Popular discussions often imply incorrectly that they do; this error is sometimes made even in materials from scientific or governmental agencies (e.g., the U.S. Environmental Protection Agency ).
Quantum mechanics provides the basis for computing the interactions between molecules and radiation. Most of this interaction occurs when the frequency of the radiation closely matches that of the spectral lines 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.)
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 spectroscopic measurements, rather than a initial quantum mechanical computations, provide the basis for most of the radiative transfer calculations used in studies of the atmosphere.
The molecules/atoms that constitute the bulk of the atmosphere: oxygen (O2), nitrogen (N2) 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 (O3). The same molecules are also the dominant infrared emitting molecules. CO2 and O3 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 vibration mode in which the molecule bends with the carbon in the middle moving one way and the oxygen’s 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 CO2 molecules will be vibration ally excited by collisions. Roughly 5% of CO2 molecules are vibration ally 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. CO2 has two other vibration 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 vibrations 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 light can be emitted and absorbed during rotational transitions, and these transitions can also be produced by collision 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 chlorofluorocarbons.
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. Gas removed percent reduction in GE
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 more than 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, runaway greenhouse effect and tipping point
The Tipping point in global warming is the point at which change due to human activity brings about sufficient new processes in nature to make any human reversal of the change impossible. Some climate scientists believe this will be reached in about 2017 while others, notably James Hansen, NASA's top climate scientist, believe it has already been reached.
When there is a loop of effects such as the concentration of a greenhouse gas itself being a function of temperature, there is a 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. Sometimes feedback effects can be on the same cause as the forcing but it can also be via another greenhouse gas or on other effects such as change in ice cover affecting the planet's Aledo.
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, 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 allowed to stop due to things 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.
According to the castrate 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 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.
A runaway greenhouse effect involving CO2 and water vapor may have occurred on Venus due to its closer proximity to the sun. 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 is 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 Venusians 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 sub ducted into the Earth by plate tectonics on geologic time scales.
Even so, the high temperatures on Venus are only partially caused by carbon dioxide; a major contributor is the thick bank of clouds containing sulphuric acid.Although these clouds give Venus a high reflectivity in the visible region, the Galileo probe showed that the clouds appear black at infrared wavelengths of 2.3 microns due to strong infrared absorption.
Anthropogenic greenhouse effect
CO2 production from increased industrial activity (fossil fuel burning) and other human activities such as cement production and tropical deforestation has increased the CO2 concentrations in the atmosphere. Measurements of carbon dioxide amounts from Mauna Loa observatory show that CO2 has increased from about 313 ppm (parts per million) in 1960 to about 375 ppm in 2005. The current observed amount of CO2 exceeds the geological record of CO2 maxima (~300 ppm) from ice core data.
Because it is a greenhouse gas, elevated CO2 levels will increase global mean temperature; based on an extensive review of the scientific literature, the Intergovernmental Panel on Climate Change concludes that "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
Over the past 800,000 years,[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. Certain pale climatologists consider variations in carbon dioxide to be a fundamental factor in controlling climate variations over this time scale.
The term 'greenhouse effect' originally came from the greenhouses used for gardening, but it is a misnomer since greenhouses operate differently. A greenhouse is built of glass. It heats up mainly because the sun warms the ground inside it and this 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): a "greenhouse" built of rock salt (which is transparent to infrared radiation) heats up just as one built of glass does. Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection It is quite common, however, to find sources that make the erroneous "greenhouse" analogy Although the primary mechanism for warming greenhouses is the prevention of mixing with the free atmosphere, the radiative properties of the glazing can still be important to commercial growers. With the modern development of new plastic surfaces and glazing for greenhouses, this has permitted construction of greenhouses which selectively control radiation transmittance in order to better control the growing environment.
See an animation of how enhancing the greenhouse effect likely contributes to global warming. (Macromedia Flash Version 5 or higher plug-in required)
Every year from 1998 through 2006 ranks among the top 25 warmest years on record for the United States, an unprecedented occurrence, according to NOAA.
Consequence: drought and wildfire
Warmer temperatures could also increase the probability of drought. Greater evaporation, particularly during summer and fall, could exacerbate drought conditions and increase the risk of wildfires.
Warning signs today
Greater evaporation as a result of global warming
Could increase the risk of wildfires.
The 1999-2002 national droughts was one of the three most extensive droughts in the last 40 years
Warming may have lead to the increased drought frequency that the West has experienced over the last 30 years.
The 2006 wild land fire season set new records in both the number of reported fires as well as acres burned. Close to 100,000 fires were reported and nearly 10 million acres burned, 125 percent above the 10-year average.
If warming continues to exacerbate wildfire seasons, it could be costly. Fire-fighting expenditures have consistently totaled upwards of $1 billion per year.
Consequence: more intense rainstorms
Warmer temperatures increase the energy of the climatic system and lead to more intense rainfall at times in some areas.
Warning signs today
National annual precipitation has increased between 5 and 10 percent since the early 20th century, largely the result of heavy downpours in some areas.
The IPCC reports that intense rain events have increased in frequency during the last 50 years, and human-induced global warming more likely than not contributed to the trend.
According to NOAA statistics, the Northeast region had its wettest summer on record in 2006, exceeding the previous record by more than 1 inch.
More frequent and more intensive heat waves could result in more heat-related deaths. Photo: Gary Braasch, Chicago, July 1995. See the World View of Global Warming website for more Gary Braasch photos illustrating the consequences of the changing climate.
Consequence: deadly heat waves and the spread of disease
More frequent and more intensive heat waves could result in more heat-related deaths. These conditions could also aggravate local air quality problems, already afflicting more than 80 million Americans. Global warming is expected to increase the potential geographic range and virulence of tropical diseases as well.
Warning signs today
In 2003, extreme heat waves claimed an estimated 35,000 lives in Europe. In France alone, nearly 15,000 people died due to soaring temperatures, which reached as high as 104 degrees Fahrenheit and remained extreme for two weeks.
Much of North America experienced a severe heat wave in July 2006, which contributed to the deaths of at least 225 people.
Studies have found that a higher level of carbon dioxide spurs an increase in the growth of weeds whose pollen triggers allergies and exacerbates asthma.
Disease-carrying mosquitoes are spreading as climate shifts allow them to survive in formerly inhospitable areas. Mosquitoes that can carry dengue fever viruses were previously limited to elevations of 3,300 feet but recently appeared at 7,200 feet in the Andes Mountains of Colombia. Malaria has been detected in new higher-elevation areas in Indonesia.
Consequence: more powerful and dangerous hurricanes
Warmer water in the oceans pumps more energy into tropical storms, making them more intense and potentially more destructive.
Warning signs today
The number of category 4 and 5 storms has greatly increased over the past 35 years, along with ocean temperature.
The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, with a record 27 named storms, of which 15 became hurricanes. Seven of the hurricanes strengthened into major storms, five became Category 4 hurricanes and a record four reached Category 5 strength.
Hurricane Katrina of August 2005 was the costliest and one of the deadliest hurricanes in U.S. history.
Consequence: melting glaciers, early ice thaw
Rising global temperatures will speed the melting of glaciers and ice caps, and cause early ice thaw on rivers and lakes.
Warning signs today
At the current rate of retreat, all of the glaciers in Glacier National Park will be gone by 2070.
After existing for many millennia, the northern section of the Larsen B ice shelf in Antarctica -- a section larger than the state of Rhode Island -- collapsed between January and March 2002, disintegrating at a rate that astonished scientists. Since 1995 the ice shelf's area has shrunk by 40 percent.
According to NASA, the polar ice cap is now melting at the alarming rate of nine percent per decade. Arctic ice thickness has decreased 40 percent since the 1960s.
Arctic sea ice extent set an all-time record low in September 2007, with almost half a million square miles less ice than the previous record set in September 2005, according to the National Snow and Ice Data Center. Over the past 3 decades, more than a million square miles of perennial sea ice -- an area the size of Norway, Denmark and Sweden combined --has disappeared.
Multiple climate models indicate that sea ice will increasingly retreat as the earth warms. Scientists at the U.S. Center for Atmospheric Research predict that if the current rate of global warming continues, the Arctic could be ice-free in the summer by 2040.
The satellite photo at far left shows the Larson B ice shelf on Jan. 31, 2002. Ice appears as solid white. Moving to the right, in photos taken Feb. 17 and Feb. 23, the ice begins to disintegrate. In the photos at far right, taken Mar. 5 and Mar 7, note water (blue) where solid ice had been, and that a portion of the shelf is drifting away. Photos: National Aeronautics and Space Administration
Consequence: sea-level rise
Current rates of sea-level rise are expected to increase as a result both of thermal expansion of the oceans and melting of most mountain glaciers and partial melting of the West Antarctic and Greenland ice caps. Consequences include loss of coastal wetlands and barrier islands, and a greater risk of flooding in coastal communities. Low-lying areas, such as the coastal region along the Gulf of Mexico and estuaries like the Chesapeake Bay, are especially vulnerable.
Warning signs today
Global sea level has already risen by four to eight inches in the past century, and the pace of sea level rise appears to be accelerating. The IPCC predicts that sea levels could rise 10 to 23 inches by 2100, but in recent years sea levels have been rising faster than the upper end of the range predicted by the IPCC.
In the 1990s, the Greenland ice mass remained stable, but the ice sheet has increasingly declined in recent years. This melting currently contributes an estimated one-hundredth of an inch per year to global sea level rise.
Greenland holds 10 percent of the total global ice mass; if it melts, sea levels could increase by up to 21 feet.
Warmer temperatures may cause some ecosystems, including alpine meadows in the Rocky Mountains, to disappear.
Consequence: ecosystem shifts and species die-off
The increase in global temperatures is expected to disrupt ecosystems and result in loss of species diversity, as species that cannot adapt die off. The first comprehensive assessment of the extinction risk from global warming found that more than one million species could be committed to extinction by 2050 if global warming pollution is not curtailed. Some ecosystems, including alpine meadows in the Rocky Mountains, as well as tropical mundane and mangrove forests, are likely to disappear because new warmer local climates or coastal sea level rise will not support them.
Warning signs today
A recent study of nearly 2,000 species of plants and animals discovered movement toward the poles at an average rate of 3.8 miles per decade. Similarly, the study found species in alpine areas to be moving vertically at a rate of 20 feet per decade in the 2nd half of the 20th century.
The latest IPCC report found that approximately 20 to 30 percent of plant and animal species assessed so far are likely to be at increased risk of extinction if global average temperature increases by more than 2.7 to 4.5 degrees Fahrenheit.
Some polar bears are drowning because they have to swim longer distances to reach ice floes. The U. S. Geological Survey has predicted that two-thirds of the world's polar bear sub-populations will be extinct by mid-century due to melting of the Arctic ice cap.
In Washington's Olympic Mountains, sub-alpine forest has invaded higher elevation alpine meadows. In Bermuda and other places, mangrove forests are being lost.
In areas of California, shoreline sea life is shifting northward, probably in response to warmer ocean and air temperatures.
Over the past 25 years, some penguin populations have shrunk by 33 percent in parts of Antarctica, due to declines in winter sea-ice habitat.
The ocean will continue to become more acidic due to carbon dioxide emissions. Because of this acidification, species with hard calcium carbonate shells are vulnerable, as are coral reefs, which are vital to ocean ecosystems. Scientists predict that a 3.6 degree Fahrenheit increase in temperature would wipe out 97 percent of the world's coral reefs.
Responses: Mitigating of global warming and adoption to global warming the threat of possible global warming has led to attempts to mitigate global warming, which covers all action aimed at reducing the negative effects or the likelihood of global warming.
How to responses the green house effects:
- Reduction of energy use
- Waste Treatment and waste management mechanism
- Shifting from carbon based fossil fuels to alternative energy sources
- Planetary engineering to cool the earth
- Massive a forestation program
- Less use of automobile that aggravate pollution
- More use of biogas fuel
- Less use of fuel and other mineral resources
- Use of more solar power and wind power
- Use of renewable energy resources
- Enhancing natural carbon dioxide gas
- Use of bio-gas and bio-diesel
- Introduction of carbon tax
- Carbon capture and shortage
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