What Process Causes Gases in the Atmosphere to Trap Heat Near the Surface of Earth
In 1827, Joseph Fourier, a French mathematician and physicist, wondered why Earth's boilerplate temperature is approximately 15°C (59°F). He reasoned that there must exist some type of residual between the incoming free 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 accept an average temperature of xv°C (59°F), Fourier knew that there had to exist some other process occurring in the atmosphere –– something similar to the mode a greenhouse retains heat. A greenhouse'south glass enclosure allows visible light to enter and be captivated by the plants and soil. The plants and soil and so emit the captivated rut energy as infrared radiation. The drinking glass of the greenhouse then absorbs that infrared radiations, emitting some of it dorsum into the greenhouse and thus keeping the greenhouse warm even when the temperature exterior is lower.
Because the two processes are like, the name "greenhouse effect" was coined to draw Fourier'south explanation. Notwithstanding, part of a greenhouse'due south warmth results from the physical bulwark of the drinking glass, which prevents the warmer air from flowing outward. Then despite the fact that the atmospheric greenhouse consequence has some processes in mutual with an actual greenhouse, the overall mechanisms driving the greenhouse effect are different and more than complex.
Greenhouse Gases
You have already learned that Earth's atmosphere is equanimous primarily of nitrogen and oxygen. These gases are transparent to incoming solar radiation. They are also transparent to outgoing infrared radiations, which means that they practise non absorb or emit solar or infrared radiations. However, there are other gases in Globe's atmosphere that do absorb infrared radiations. These gases are known every bit greenhouse gases. Below are the virtually important greenhouse gases that influence Earth'southward climate arrangement.
H2o vapor (H2O) 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 as much moisture as the air can at that temperature), the excess moisture will condense into cloud droplets. And if these droplets are large plenty, they will fall equally precipitation.
Carbon dioxide (CO2) is also an important greenhouse gas. It has a long lifetime in Earth's atmosphere. Carbon dioxide strongly absorbs energy with a wavelength of 15 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 four major processes: photosynthesis, respiration, organic decomposition or decay, and combustion or the burning of organic fabric. You lot will learn more about carbon dioxide and the carbon cycle in Module four.
Methane (CH4) is 30 times stronger than carbon dioxide as an absorber of infrared radiation. Methyl hydride, yet, is nowadays in smaller concentrations than carbon dioxide, so its net contribution to the greenhouse result is not as large. Methane is also relatively short-lived (lasting approximately 8 years) in the atmosphere. Methyl hydride is produced when bacteria decompose organic plant and animal matter in such places equally wetlands (e.k., marshes, mudflats, flooded rice fields), sewage treatment plants, landfills, and the guts of cattle and termites. Scientists are concerned near the concentration of methane increasing in regions where the Chill and alpine permafrost is thawing and releasing methane equally it warms.
Halocarbons are composed of carbon, chlorine, fluorine, and hydrogen. They include chlorofluorocarbons (CFCs), which are human-fabricated gases commonly used in refrigerators and air conditioners. Concentrations of Cfc gases in the temper are the highest of any of the halocarbons, and they can blot more than infrared radiations than whatever other greenhouse gas. The impact of 1 molecule of a CFC gas is equivalent to 10,000 molecules of carbon dioxide.
Nitrous oxide (N2O), a relatively long-lived gas, has increased in atmospheric concentration due mainly to agriculture. Nitrate (NO3-) and ammonia (NH4+) are used equally fertilizers. Bacteria convert a small amount of this nitrate and ammonia into the form 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 low concentrations in the troposphere (the lowest layer of the atmosphere). In the troposphere, information technology is produced by a combination of pollutants — generally hydrocarbons and nitrogen oxide compounds.
In the 1860s, John Tyndall, an Irish gaelic scientist who was fascinated by the growth and formation of glaciers, wanted to exam his ideas explaining how Earth maintained a fairly constant temperature. He began a series of experiments to mensurate the amount of radiant heat (infrared radiations) that certain gases could blot and transmit. Tyndall found that water vapor and carbon dioxide were expert absorbers and emitters of infrared radiation.
The relative importance of a greenhouse gas depends on its abundance in Earth's temper and how much the gas tin absorb specific wavelengths of free energy.
An effective absorber of infrared radiation has a broader absorption profile, which means that information technology can absorb a wider spectrum of wavelengths. Water vapor and carbon dioxide can absorb radiation wavelengths in the range of 4 μm to fourscore μm, except those between 8 μm and 12 μm. Ozone can blot wavelengths between 9 μm and x μm, but as you have learned, information technology is found in low concentrations. The sun's ultraviolet wavelengths are strongly absorbed by ozone in the stratosphere.
How the Greenhouse Effect Works
The dominicus's visible wavelengths of radiation pass easily through the atmosphere and reach Globe. Approximately 51% of this sunlight is absorbed at Earth's surface past the land, h2o, and vegetation. Some of this energy is emitted dorsum from the Globe's surface in the course of infrared radiations.
Water vapor, carbon dioxide, methyl hydride, and other trace gases in Earth'due south atmosphere absorb the longer wavelengths of outgoing infrared radiation from Globe's surface. These gases then emit the infrared radiation in all directions, both outward toward space and downward toward Earth. 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 Earth to be warmer than it otherwise would be. This process is known as the natural greenhouse consequence and keeps Earth's average global temperature at approximately xv°C (59°F).
I. The sun'south visible wavelengths of radiation pass easily through the temper and reach Earth. Approximately 51% of this sunlight is absorbed at Earth's surface by the land, water, and vegetation.
Two. Some of this energy is emitted from Earth's surface back into space in the form of infrared radiation.
Iii. Much of this infrared radiations does non reach space, yet, because information technology is captivated by greenhouse gases in temper, and is and so emitted as infrared radiation back toward the Earth's surface. This procedure is known as the greenhouse outcome.
If the concentration of greenhouse gases increases, then more infrared radiation volition be absorbed and emitted back toward Earth's surface, creating an enhanced or amplified greenhouse effect.
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| Certain human activities emit additional greenhouse gases to the temper and increase the amount of heat that gets absorbed earlier escaping to space, thus enhancing the greenhouse consequence and amplifying the warming of the earth. | |
When averaged over the course of a yr, the amount of incoming solar radiation received from the sun has balanced the amount of outgoing energy emitted from Earth. This equilibrium is called Earth'southward free energy or radiations balance. Relatively small changes in the amounts of greenhouse gases in Globe's temper can profoundly modify that balance between incoming and approachable radiation. Earth then warms or cools in club to restore the radiative rest at the top of the temper.
Source: http://www.ces.fau.edu/nasa/module-2/how-greenhouse-effect-works.php
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