How come CO2 doesn't reflect energy coming in from the sun?
CO2 reflects energy coming back from the Earth, right? Why doesn't it also reflect energy directly coming in from the sun back, thus making the planet colder ?
- speakeasyLv 61 decade agoFavorite Answer
These answers are about right - the Earth radiates heat in certain infrared spectrums that are allegedly trapped by CO2. However, CO2 is very poor at trapping heat.
That's why the Sahara Desert goes from over 120 degrees in the daytime to freezing at night. CO2 cannot trap heat even for a few hours, much less over the long periods of time necessary to make a global difference.
Water vapor, however, is a very good heat sink. It constitutes 95% of the atmosphere's heat-trapping capability. That's why the Amazon only loses about five degrees overnight.
When this current warming cycle started, about 18,000 years ago, it was due to increased solar energy warming oceans and vaporizing water that trapped atmospheric heat and releasing CO2 gas to feed the plant life.
Think about it.Source(s): Water Vapor Rules the Greenhouse System http://www.geocraft.com/WVFossils/greenhouse_data.... Clues to End of the Last Ice Age - increased solar output warmed oceans, melting ice and releasing CO2 http://www.usc.edu/uscnews/stories/14288.html
- Anonymous4 years ago
Objects emit light depending on their temperature. That's why pottery glows in kilns, or swords glow when they're in a furnace. This is called 'Blackbody radiation'. The type of light given out by a blackbody is modeled by 'Planck's law of blackbody radiation'. If you look at the graphs, you'll see that both the amount of light, and the wavelength of the light, depends on the temperature of the material. Hotter means more light and shorter wavelengths. Cooler means less light and longer wavelengths. The surface of the Sun is something like 6,000-6,600 degrees Kelvin. (about 5,700-6,200 celsius). The surface of the Earth is something like 290K (17 celsius). So most of the light from the Sun is at smaller wavelengths than the light emitted by Earth. Materials only absorb light of specific wavelengths, when the energy of a photon is roughly the same as the difference in electron energy levels. If you've done upper school physics or chemistry you'll know this, if you haven't, then you'll have to accept this is a fundamental result of quantum mechanics! The energy bands in CO2 are just the right size to absorb a lot more photons coming up from Earth than photons coming down from the Sun, so it stops a decent amount of heat escaping upwards, but barely anything coming down. 'Global dimming' was not from CO2, but from aerosols which are big enough to directly reflect incoming sunlight.
- d/dx+d/dy+d/dzLv 61 decade ago
All gasses in the atmosphere absorb and scatter photons. The relative magnitudes of these processes varies with wavelength for each type of gas. Further, the processes are exactly the same whether radiation is incoming or outgoing. The sun does radiate in the infrared and CO2 at the top of the atmosphere absorbs and radiates about half of the incoming infrared radiation at frequencies near 700 cm-1back into space. There is also outgoing infrared radiation that is absorbed and re-radiated back to earth. The earth radiates much more infrared radiation than it receives from the sun so the NET effect is that more infrared radiation is emitted toward the earth as the CO2 concentration increases. In the visible and ultraviolet regions, CO2 can also absorb incoming photons via electronic transitions and the radiative transport is similar to the infrared case, except that the net flux is outgoing. This effect is about 1E-12 weaker than the infrared case. CO2 can also scatter radiation elastically (Rayleigh) and inelastically (Raman) and thus contributes to the blue sky. These processes scale with (frequency)^4 and are typically 1-E6 to 1E-8 weaker than absorptions at the same frequency. Scattering is strong at the UV end of the spectrum and quite weak in the infrared, which is why you see sunsets. An important exception to this generalization is if the frequency of the photon corresponds to an electronic transition energy (resonance) in which case the scattering is enhanced by a factor or 1E6 or more.
- pegminerLv 71 decade ago
First, it doesn't reflect energy, it absorbs infrared. Most of the sun's energy is visible light, not infrared, and CO2 is transparent to visible, letting it pass down to the Earth's surface (like all the other gases). Once the Earth's surface heats up, it radiates infrared back toward space--that is what CO2 absorbs.
EDIT: Speakeasy, can you give a source for your assertions about the Sahara? Specifically, what is the precipitable water (total column water vapor) over the Sahara? How does it compare to other places in the world?
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- DifdiLv 61 decade ago
CO2 traps heat. Most of the energy in sunlight is not in the form of heat. Heat is produced when that non-heat energy strikes matter (including atmospheric gasses). For example, a microwave oven works by beaming microwaves through the food, which get blocked by water, among other things -- When the microwaves are blocked, the energy in them is converted into heat.
- DavidLv 61 decade ago
It doesn't really reflect the energy coming from the earth, it absorbs it and re-emits it.
It's all about the wavelength. CO2 can only absorb at very specific wavelengths. Some of these wavelengths happen to be emitted by the earth. The ones emitted by the sun are too short to be absorbed by CO2.
- bob326Lv 51 decade ago
"CO2 traps heat. Most of the energy in sunlight is not in the form of heat. Heat is produced when that non-heat energy strikes matter (including atmospheric gasses). For example, a microwave oven works by beaming microwaves through the food, which get blocked by water, among other things -- When the microwaves are blocked, the energy in them is converted into heat."
This is mostly wrong.
- x1yofuzzy1xLv 41 decade ago
because its a clear gas. it acts as an insulator trapping the heat energy here. the sun energy is light and light can pass straight through co2
- 1 decade ago
Because it's made up.