[BillM]

I really object to calling "global warming" a theory. Evolution, gravity, relativity--those are all theories. They are all supported by massive amounts of data. However, I do not see much evidence or data to back up the claim that carbon dioxide has a disproportionate effect on climate. I see speculations--e.g. "Sea levels expected to rise between 1 and 3 meters"--but no hard evidence that adding carbon dioxide to a gas mix has any more of an effect on its ability to retain heat than adding water vapor. To be correct, one would have to call anthropogenic global warming a hypothesis, which is scientificese for "educated guess." I am still waiting to see this hypothesis undergo experimental controlled tests.

Quite to the contrary, Water in the atmosphere has enormously more effect that CO2.

From Miltonconservative

This is THE ESSENSE of the GREENHOUSE EFFECT.
Enormous amounts of energy (principally translational and vibrational) are carried from the surface into the atmosphere by fast moving free or loosely associated water molecules.
Collisions between water molecules and the majority nitrogen and oxygen molecules transfer the energy to the greater atmosphere. As the energy level of the water molecules diminishes, the probability that water molecules will reaggregate increases. This leads to condensation and has the effect of transferring that 539 calories per gram to the rest of the atmosphere.
Now for the Kicker!
Carbon dioxide does NOT form aggregates. It is not lighter than air and thus does not rise quickly. There is no phase change when carbon dioxide enters the atmosphere. Carbon dioxide carries less than half the heat per molecule compared to water.
One gram of Carbon Dioxide heated at the surface by incident sunlight carries (2 * 539 = 1078) 1078 times less energy into the atmosphere than one gram of water.
Carbon dioxide represents 0.0387 % of the atmosphere. Water in the lower atmosphere represents 1% to 4% or 25 to 100 times the amount of carbon dioxide.
Combining the two statements above, Water is (25 * 1078 = 27,175) to (100 * 1078 = 108,700) times more responsible for greenhouse effect than carbon dioxide.

[exDemMom]

That’s a very interesting explanation of the greenhouse effect, and it makes a lot more sense than other explanations I have seen.

I have often questioned what it is about CO2 that supposedly gives it such a disproportionate ability to increase total atmospheric heat (energy) content. No one has ever been able to explain it, even those who are rabid advocates of the AGW hypothesis.

One explanation that I have seen is that CO2 has an unusually broad fluorescence band in the IR range. However, that does not make sense as a mechanism for retaining energy, since fluorescent absorption and emission happen almost instantaneously. Someone told me that during the nanoseconds between absorption and emission, the CO2 molecule can shed that energy by bumping another molecule. In that case, the atmosphere would have to be of a certain density for that mechanism to have any effect. Without that critical density, the shedding of energy by fluorescent emission would be the primary way the CO2 loses the energy gain of fluorescent absorption.

Your description of the greenhouse effect makes far more sense. The energy change of phase transition of water accounts for a lot of energy—and, of course, CO2 under normal atmospheric conditions only undergoes one phase transition at a very low temperature, lower than that encountered almost anywhere on earth. So CO2 cannot store energy, while water does.

Thank you.