The energy from the photon causes the CO 2 molecule to vibrate. Some time later, the molecule gives up this extra energy by emitting another infrared photon.
Once the extra energy has been removed by the emitted photon, the carbon dioxide molecule stops vibrating. This animation is somewhat of a simplification. Molecules are constantly in motion, colliding with other gas molecules and transferring energy from one molecule to another during collisions. In the more-complex, real-world process, a CO 2 molecule would most likely bump into several other gas molecules before re-emitting the infrared photon.
Internal combustion engines also 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, it is produced by a combination of pollutants — mostly hydrocarbons and nitrogen oxide compounds. In the s, John Tyndall, an Irish scientist who was fascinated by the growth and formation of glaciers, wanted to test his ideas explaining how Earth maintained a fairly 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 found 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 Earth's atmosphere and how much the gas can absorb specific wavelengths of energy.
An effective absorber of infrared radiation has a broader absorption profile, which means that it can absorb a wider spectrum of wavelengths. The sun's ultraviolet wavelengths are strongly absorbed by ozone in the stratosphere. The sun's visible wavelengths of radiation pass easily through the atmosphere and reach Earth.
Some of this energy is emitted back from the Earth's surface in the form of infrared radiation. Water vapor, carbon dioxide, methane, and other trace gases in Earth's atmosphere absorb the longer wavelengths of outgoing infrared radiation from Earth'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.
Some of this energy is emitted from Earth's surface back into space in the form of infrared radiation. Much of this infrared radiation does not reach space, however, because it is absorbed by greenhouse gases in atmosphere, and is then emitted as infrared radiation back toward the Earth'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 effect. When averaged over the course of a year, 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's energy or radiation balance.
Relatively small changes in the amounts of greenhouse gases in Earth's atmosphere can greatly alter that balance between incoming and outgoing radiation. Some of this energy is transferred to the atmosphere by conduction and convection. The Earth also radiates lower frequency infrared radiation.
Some of this infrared radiation is transmitted through the atmosphere back out into space, and some is absorbed by greenhouse gases in the atmosphere. The greenhouse gases emit infrared radiation in all directions — some out into space and some back towards Earth, which is then reabsorbed.
This allows the planet to support life.
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