What gas allows Earths atmosphere to absorb and maintain heat?
In 1827, Joseph Fourier, a French mathematician and physicist, wondered why Earth's average temperature is approximately 15°C (59°F). He reasoned that at that place must be some type of balance between the incoming energy and the outgoing energy to maintain this fairly constant temperature. His calculations indicated that Globe should actually be much colder (-18°C or 0°F).
To have an average temperature of 15°C (59°F), Fourier knew that there had to be another process occurring in the atmosphere –– something similar to the way a greenhouse retains heat. A greenhouse's glass enclosure allows visible light to enter and be captivated by the plants and soil. The plants and soil then emit the absorbed heat energy as infrared radiation. The glass of the greenhouse then absorbs that infrared radiation, emitting some of it dorsum into the greenhouse and thus keeping the greenhouse warm even when the temperature outside is lower.
Because the two processes are similar, the name "greenhouse event" was coined to draw Fourier'south explanation. However, role of a greenhouse's warmth results from the physical barrier of the glass, which prevents the warmer air from flowing outward. And so despite the fact that the atmospheric greenhouse effect has some processes in common with an actual greenhouse, the overall mechanisms driving the greenhouse consequence are different and more complex.
Greenhouse Gases
You take already learned that Earth's atmosphere is composed primarily of nitrogen and oxygen. These gases are transparent to incoming solar radiation. They are also transparent to outgoing infrared radiation, which means that they practice not blot or emit solar or infrared radiations. However, there are other gases in Earth'due south atmosphere that do blot infrared radiation. These gases are known as greenhouse gases. Below are the most important greenhouse gases that influence Earth'southward climate system.
Water vapor (Water) is the strongest greenhouse gas, and the concentration of this gas is largely controlled by the temperature of the atmosphere. As air becomes warmer, it can hold more wet or water vapor. When the air becomes saturated (or holds every bit much moisture as the air tin at that temperature), the excess moisture will condense into cloud droplets. And if these droplets are large enough, they will fall as precipitation.
Carbon dioxide (CO2) is also an important greenhouse gas. It has a long lifetime in Globe's atmosphere. Carbon dioxide strongly absorbs energy with a wavelength of xv μm (micrometers). This makes carbon dioxide a good absorber of wavelengths falling in the infrared radiation region of the spectrum.
Carbon dioxide constantly moves into and out of the atmosphere through iv major processes: photosynthesis, respiration, organic decomposition or disuse, and combustion or the called-for of organic material. Y'all will learn more about carbon dioxide and the carbon bike in Module 4.
Methane (CH4) is 30 times stronger than carbon dioxide as an absorber of infrared radiation. Methyl hydride, yet, is present in smaller concentrations than carbon dioxide, and so its net contribution to the greenhouse effect is not equally large. Methane is likewise relatively curt-lived (lasting approximately 8 years) in the atmosphere. Methyl hydride is produced when bacteria decompose organic plant and animal matter in such places as wetlands (due east.yard., marshes, mudflats, flooded rice fields), sewage treatment plants, landfills, and the guts of cattle and termites. Scientists are concerned about the concentration of methane increasing in regions where the Arctic and alpine permafrost is thawing and releasing methyl hydride equally it warms.
Halocarbons are composed of carbon, chlorine, fluorine, and hydrogen. They include chlorofluorocarbons (CFCs), which are human being-made gases unremarkably used in refrigerators and air conditioners. Concentrations of CFC gases in the temper are the highest of whatever of the halocarbons, and they can absorb more than infrared radiations than any other greenhouse gas. The impact of 1 molecule of a CFC gas is equivalent to ten,000 molecules of carbon dioxide.
Nitrous oxide (N2O), a relatively long-lived gas, has increased in atmospheric concentration due mainly to agronomics. Nitrate (NO3-) and ammonia (NH4+) are used every bit fertilizers. Bacteria convert a minor amount of this nitrate and ammonia into the course of nitrous oxide. Internal combustion engines too produce nitrous oxide.
Ozone (O3) is also a relatively minor greenhouse gas because it is found in relatively depression concentrations in the troposphere (the lowest layer of the atmosphere). In the troposphere, it is produced past a combination of pollutants — generally hydrocarbons and nitrogen oxide compounds.
In the 1860s, John Tyndall, an Irish scientist who was fascinated by the growth and formation of glaciers, wanted to exam his ideas explaining how World maintained a adequately constant temperature. He began a series of experiments to measure the amount of radiant heat (infrared radiation) that certain gases could absorb and transmit. Tyndall establish that water vapor and carbon dioxide were good absorbers and emitters of infrared radiation.
The relative importance of a greenhouse gas depends on its abundance in World'south atmosphere and how much the gas tin can absorb specific wavelengths of energy.
An effective absorber of infrared radiations has a broader assimilation profile, which means that it can absorb a wider spectrum of wavelengths. Water vapor and carbon dioxide tin can absorb radiation wavelengths in the range of 4 μm to eighty μm, except those between viii μm and 12 μm. Ozone can absorb wavelengths between ix μm and 10 μm, merely as you lot have learned, it is establish in low concentrations. The sun's ultraviolet wavelengths are strongly absorbed past ozone in the stratosphere.
How the Greenhouse Effect Works
The dominicus'due south visible wavelengths of radiation pass hands through the temper and reach Earth. Approximately 51% of this sunlight is absorbed at Earth's surface by the state, h2o, and vegetation. Some of this energy is emitted back from the Earth'south surface in the class of infrared radiations.
Water vapor, carbon dioxide, methane, and other trace gases in Earth's atmosphere absorb the longer wavelengths of outgoing infrared radiation from Globe's surface. These gases and then emit the infrared radiations in all directions, both outward toward space and downward toward World. This process creates a second source of radiation to warm to surface – visible radiation from the sun and infrared radiation from the atmosphere – which causes Globe to be warmer than it otherwise would be. This process is known as the natural greenhouse effect and keeps Earth's average global temperature at approximately 15°C (59°F).
I. The sun's visible wavelengths of radiation pass hands through the atmosphere and reach World. Approximately 51% of this sunlight is absorbed at Globe's surface past the land, water, and vegetation.
II. Some of this energy is emitted from Earth's surface dorsum into space in the course of infrared radiations.
Iii. Much of this infrared radiation does not reach space, however, because it is absorbed by greenhouse gases in temper, and is then emitted as infrared radiations dorsum toward the Globe's surface. This process is known as the greenhouse effect.
If the concentration of greenhouse gases increases, then more infrared radiation will be absorbed and emitted back toward Earth's surface, creating an enhanced or amplified greenhouse result.
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| Certain homo activities emit additional greenhouse gases to the atmosphere and increase the amount of heat that gets absorbed earlier escaping to space, thus enhancing the greenhouse outcome and amplifying the warming of the earth. | |
When averaged over the grade of a twelvemonth, the amount of incoming solar radiations received from the lord's day has balanced the corporeality of outgoing energy emitted from Earth. This equilibrium is chosen Earth's energy or radiation balance. Relatively modest changes in the amounts of greenhouse gases in Earth'south atmosphere can greatly alter that remainder between incoming and outgoing radiations. World then warms or cools in society to restore the radiative residue at the superlative of the atmosphere.
Source: http://www.ces.fau.edu/nasa/module-2/how-greenhouse-effect-works.php
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