Without getting technical, the greenhouse gases work because they have the capacity to trap heat as it tries to escape from Earth into space. This happens because the vibrational frequency of the greenhouse gas molecules corresponds with the wavelengths of thermal radiation, this allows for the absorption and subsequent retransmission of the heat energy; it’s this process that we call the greenhouse effect.
Thermal radiation (infrared heat energy) is given off by Earth and the various things on it. It’s different from the heat coming at us from the Sun, this is solar radiation and has a different frequency to thermal radiation. This difference in wavelengths allows heat from the Sun to pass through our atmosphere and not get absorbed by the greenhouse gases. The heat from the Sun warms the land and the oceans and then, as the temperature falls, this absorbed energy is radiated back out, only now it’s thermal radiation and can be absorbed by the greenhouse gases.
This change from one type of radiation to another occurs due to the temperature of the medium emitting the heat – the hotter it is the more energetic the heat and the shorter the wavelength.
It is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface and the lower atmosphere, it results in an elevation of the average surface temperature above what it would be in the absence of the gases.
When visible light strikes the Earth most of it turns to heat, which in turn is re-radiated upward in the IR band.
Any gas having significant 'absorption' bands in the IR range will capture some of this heat & some of the captured heat will re-radiate back to Earth... thus making the planet warmer.
One important thing to understand about this effect is that it's logarithmic... namely that as a given gas reaches the point where it has absorbed most the energy in a given band, higher concentrations have less & less effect.
Picture an umbrella that cuts 50% of the light. A second umbrella will cut the light by only 25% more. A 3 umbrella only by 12.5%. So in essence, what ever concentration of a give gas absorbs half the available energy, each doubling will result in half the given effect of the prior doubling.
This is important because the 'Religion' of AGW, which pretty much evolved to promote Socialist control over Free Market Energy, ignores the fact that CO2 has apparently reached a point of effective 'saturation'. (or more accurately the 'insensitive' part of the curve)
So for example, if you graduated from High School this year, there has been no Global Warming since the time you entered Kindergarten.
the green house gases do nothing when the heat is coming fro the sun. but after hitting the earth, when this heat trying to reflect and go outside. the green house gases stopped this and preserve it. in this way the green house gases helps to warm the earth's atmosphere. though now a days, these gases are increased very much in our atmosphere and that's why, the earth is getting hot to hotter which is not wanted. so we need to control these green house gases.
Earth emits light in the infrared range (3 -70 microns) http://en.wikipedia.org/wiki/Black-body_...
rather than the visible range like the sun does (0.1 - 3 microns). http://en.wikipedia.org/wiki/File:Atmosp...
If Earth emits more energy to outer space than she absorbs from the sun, she cools. If she emits less, she warms. Metastability http://en.wikipedia.org/wiki/Metastabili...
is achieved when Earth reaches a temperature at which increasing the temperature causes enough of an increase in Earthlight escaping to outer space to bring the temperature back to where it was before, and decreasing the temperature causes a sufficient drop in Earthlight output to keep the temperature stable within a relatively narrow range. http://en.wikipedia.org/wiki/Homeostasis
Greenhouse gases (H2O, CO2, halocarbons) are those which tend to absorb earthlight more than they block sunlight. http://randombio.com/co2.html
Once a photon is absorbed (earthlight or sunlight), the gas then re-emits a photon in a random direction that might not be at the same wavelength (color) as the original photon it absorbed. If it is emitted toward outer space, and has a wavelength that is not efficiently absorbed by gases in the atmosphere, it will escape unmolested. Otherwise, it will either head back to Earth if pointed in that direction, and/or possibly be absorbed again if was emitted at a wavelength that is easily absorbed. http://answers.yahoo.com/question/index;...
Thus, the Earthlight escaping to outer space is reduced. Earth is 33 kelvins warmer in order to produce more Earthlight to make up for the Earthlight that does not escape. The equation is:
j = σT^4 = Power radiated per area = Earthlight/m^2 http://en.wikipedia.org/wiki/Stefan-Bolt...
σ = a constant that depends on units and greenhouse gases and a few other things
T = absolute temperature (kelvins) http://en.wikipedia.org/wiki/Thermodynam...
j = σT^4 = Sunlight absorbed by Earth for homeostasis
Aside from greenhouse gases which absorb earthlight more efficiently than sunlight, there are gases like O3 (ozone) that absorb sunlight more efficiently than earthlight. These are anti-greenhouse gases. The IPCC believes (with good reason) that adding more O3 to the atmosphere will warm Earth rather than cool Earth. http://www.ipcc.ch/publications_and_data...
This is because, there is already enough O3 in the atmosphere to nearly completely block UV light from the sun (< 300 nm), but not yet enough to complete all the earthlight that it absorbs less efficiently (10 microns). [1] To some extent CO2 and CH4, which are greenhouse gases that also absorb sunlight less efficiently also saturate, and start to have a cooling effect at some concentration. The greenhouse gases that are not saturated are halocarbons, and they can explain all of the recent warming [2] by themselves. [3]
I did'nt know they did. In order for greenhouse gases to warm a planet, you'd have to have 98% of the planet all greenhouse's. I wonder how a greenhouse produce's gas, when it grows green plants that create oxygen. MIKE
All the green house gases absorbs excessive heat from the sunlight and can't give chance to escape from the environment or atmosphere.so the green house gases warm the earth's atmosphere.i hope you understood thankyou
confusing factor look into in google that can help
