If c02 reflects infrared energy back to earth , why doesn't the c02 below reflect it right back out?

Question

co2 is about 50% heavier than air

co2 is about 380 parts per million of the atmosphere, by volume, 590 ppm by weight. this is 1/1695th

since the weight of the atmosphere is equal to 30"of mercury,

the weight of the co2 component would equal .0176" in.hg.

this seems like a hair on the tail,wagging the whole dog

Answer 1

It does not reflect infared radiation, it absorbs it raising the energy level of the molecules (i.e. they get hotter).  Some of this heat is then transferred to other molecules in the atmosphere via conduction.

Answer 2

The percentage of the entire atmosphere composed of CO2 is a red herring.  Neither oxygen or nitrogen (combined +98% of our atmosphere) are green house gases, so they are not a factor in the equation when you deal with the 15C mean warming caused by green house gases.  

Most studies reveal that CO2 is responsible for between 10% & 25% of all green house caused warming.  Thus, a 30% (and growing) increase in CO2 is a lot more than a hair on the tail of a dog.  While it's more complex than a direct linear correlation, for simplicity sake a linear analysis at least gives a ballpark:

CO2 is responsible for 1.5C - 3.75C

+30% means 0.45C - 1.125C warmer

A doubling of CO2 would be 1.5C - 3.75C warmer

From over 61 scientific papers done in the past 110 years on the climate sensitivity to a CO2 doubling, the average estimated warming is about 2.86 C.  The more recent studies are converging at around 3.15 C.

Edit:

d/dx excellent answer.

Answer 3

it's not really about being reflective, it's about energy absorbtion.

As a gas, carbon dioxide is clear (using the greenhouse analogy, it's the glass)

Light is converted to heat by earth's surface, then the carbon dioxide insulates the heat.

Answer 4

Infrared radiation is not reflected by CO2.  CO2 absorbs and re-radiates infrared radiation.  The net effect is very much like reflection, but this is not the correct explanation.  It is better to think of the propagation of radiation as a diffusive process in the lower atmosphere.  In fact, infrared radiation is travels upward by a very torturous path (it goes up and down many times before finally escaping to space) and this is precisely why there is more radiant energy at lower elevations.  If you put your hand in front of a bright light, some radiation will diffuse through.  However, the part of your hand closest to the light will have the highest concentration of photons and will appear the brightest.  The mean free path for visible photons in your hand is about 1/3 of a mm.  In the atmosphere the mean free path for infrared photons varies, depending on pressure, from a few cm to many km, but the basic physics is the similar. (Scattering at cell boundaries rather than absorption and re-emission is the dominant process for visible photons in your hand.)  

The second part of your question is essentially why does a small amount of CO2 matter.  The answer is that CO2 has an infrared absorption cross section that is a billion to a trillion times larger than N2 or O2 (depending on wavelength). The absorption cross sections are published in a standard reference known as the HITRAN spectral database.  You need to multiply the concentration by the absorption cross section to get the overall effect.  You will find that CO2 is in fact much more important than N2 or O2 for radiative transport in the atmosphere.  The same will hold for H2O, CH4 and a host of less abundant organic molecules.

Edit:  The paper referenced by Rick above contains significant errors.  Dr. Hug is doing the wrong experiment with the wrong spectrometer.  The earth is not 1100 C.  The attenuation measured by Dr. Hug is the not unsurprising result  that air at 15 C radiates less than a globar at 1100 C.  Dr. Hug's instrument has 2 cm-1 resolution, whereas an instrument with 0.01 cm-1 or better resolution is required to do the experiment properly.  High resolution FT spectrometers  suitable for atmospheric measurements have historically been made by Bomen.   Dr. Hug is stumbling on a topic in 1998 was dealt with comprehensively by Dr. Hertzberg in the 1940's.  Dr. Hertzberg's contributions to molecular spectroscopy were recognized with a Nobel Prize in Physics in 1971.  Dr. Hug is 50 years late, still wrong, and is frankly nowhere close to Nobel material.

Edit 2:  Ben O, yes a very bright source of IR is very desirable for measuring the absorption spectrum.  Contrast is needed.  I can, and have measured spectra using my hand as a heat source.  The S/N is much worse than the globar, but well within my instument's capability.  Thats why I said that Hug is doing the wrong experiment.  The emission and absorption are balanced in a gas at constant temperature.  Hug's fatal error is that he completely ignores emission side of the equation. Although virtually all of the initial photons emitted from the earth are absorbed in less than a meter, these photons are replaced with an equivalent number (I use the term loosely because there is a change in the spectral distribution because gas molecules have discrete spectra and are not black body radiators) of photons emitted by gas molecules in the air (at the same temperature as the ground).

Answer 5

CO2 doesn't reflect energy.  The atmosphere, and the ground both absorb and emmit infrared radiation.

Heat will always move from from hotter objects to cooler objects in accordance with the second law of thermodynamics.  If the atmosphere is cooler than the earth, radiation energy will move from the earth to the atmosphere.

(edit) d/dx Are you serious?  If you want to measure the absorbtion spectrum of a gas you need an intense source of infrared radiation.  

If you have a room temperature source there will be no absorbtion at all as the gas will radiate the same amount of energy it absorbes, in accordance with the second law of thermodynamics.  Net absorbtion (difference between radiation absorbed and radiation emitted) would be zero.

Answer 6

That's actually a good question (despite the tone it was asked in). So I'll try to answer as best I can. The simple answer is that the greenhouse effect is actually more complicated than most people realize. It isn't just a matter of greenhouse gases "trapping" heat and keeping it from escaping to space.

Most descriptions of the greenhouse effect you find describe the effect as a sort of net that "catches" energy before it escapes to space. A better way of thinking about the greenhouse effect is like a dam built across a river. Just like the river slows the water moving downstream and locally deepens the river, the greenhouse effects slows the energy moving from Earth to space and locally heightens the temperature at Earth's surface. In other words, the greenhouse effect doesn't "trap" energy in the atmosphere, it simply slows the rate energy is able to escape to space.

Another important fact is that greenhouse gases don't reflect energy back to Earth. Rather, they absorb some of the upward energy radiated by the Earth, then re-radiate half of it "up" toward space, and half back "down" to Earth. So you're absolutely right that the lower gases will absorb some of the downward radiation. However, all of this energy eventually will be radiated to space (remember that the greenhouse effect only slows it down), so the overall effect is that energy is escaping to space at the same speed it's coming in from the sun.

The reason then, that changing the concentration of greenhouse gases can affect the planet's temperature should be clear. Physics tells us that in order to stay at a constant temperature, Earth has to radiate energy at the same speed it is absorbing energy from the sun. If energy is coming in faster than it's than going out, Earth will warm. If it's going out faster than it's going in, Earth will cool. So adding greenhouse more greenhouse gases will slow the energy leaving Earth, and Earth will have to warm up to compensate for it.

Hopefully that answers your question. But if it's still confusing, I've included several links in the sources to some more in depth discussions of the greenhouse effect.

As to the several points you raised in the details:

1) It's true that CO2 is heavier than air. But it's irrelevant, since CO2 is a well mixed gas.

2) Again, it's true that CO2 only makes up a very tiny portion of the atmosphere. But again, it's irrelevant because CO2 makes up 9-36% of the overall greenhouse effect (the range is due to spectral overlap with the other absorbers).

Answer 7

I'd like to counter the "asker" (who seems to have more of a rant than a question) with two similar questions:

- How much water does it take to make clear air opaque with fog?

- How much cyanide does it take to make a healthy meal fatal?

Would those things also be "tails wagging dogs"?

Greenhouse gases don't reflect like mirrors; they scatter, like clouds.  Photons in the absorbing range random-walk through them until they are either absorbed (and re-emitted at some other wavelength, which may also be in the absorbing range) or escape.  The greater the concentration of greenhouse gases, the less distance the average IR photon travels before being scattered or absorbed. 

Answer 8

Clever & true - "Hair on the tail, wagging the whole dog."

You might want to read - Dr. Heinz Hug - - A Spectroscopic Artifact?   As well as "Reactions to Dr Hug's controversial paper (downloadable zip file) here"

http://www.john-daly.com/artifact.htm

Very informative - It could be the IPCC exaggerated the absorptive effects by 40 to 80 times?

Funny that some people regurgitate false science like:

"Another important fact is that greenhouse gases don't reflect energy back to Earth. Rather, they absorb some of the upward energy radiated by the Earth, then re-radiate half of it "up" toward space, and half back "down" to Earth."

Intelligent people know that infra red emits from a molecule in an omni directional manner = basically in 6 directions.  

Ergo only one sixth could radiate 'back to earth'.

When temperatures did not follow the continually increasing CO2 levels after 1998 - More scientists began to question the Theory and the Alarmists seem to get more and more irrational!!

+

Oceans regulate CO2 in the atmosphere totally and rapidly through equilibrium exchanging 19 times as much C02 as humans produce.

Almost no energy leaves the earth’s surface as radiation to be absorbed. Almost all exits through conduction, convection and evaporation.

http://www.nov55.com/gbwm.html

Answer 9

there have been many good answers and i would just like to add.

Ben O

Second law of thermodynamics is related to increasing entropy. not to radiation unless you are referring to temps averaging out.

Answer 10

because the infrared energy going back into space is a different wavelength than the solar energy coming from the sun.

that answers the subject.

which has nothing at all to do with the description.

and there is not a question in the description.

other than the implication that there is insufficient CO2 to make a difference.

however, if you've not studied enough to understand the difference that the wavelength makes, it would seem to me that you might consider that the PhDs that are actually doing the research might know more about the problem than you do.

Answer 11

First, your question.  Indeed, some of the CO2 headed back down gets reflected back up.  But some doesn't.  Basically CO2 molecules bat heat around like a ping pong ball, and some goes back to the Earth.  So the Earth heats up. Slowly, but enough to cause great damage over the next 25-50 years.  And it will take us at least that long to fix this, so we need to start now.

I know it seems hard to understand that such a small change can have such a big effect.  But, chemicals often have effects that are enormous, even in small quantities.  The scientists can calculate theoretically how much heat a certain amount of CO2 will cause the Earth to retain.  It corresponds closely to the observed temperature rise.