The process where vibrational energy is transferred as kinetic energy is called V-T collisional relaxation. It is not particularly efficient, maybe 1 in 1000 collisions, but the average collision time at atmospheric pressure is ~ 0.1 ns. so you get a time of ~ 10 microseconds.

If you want a model of what happens, think of the collision partner approaching one end of a vibration molecule, the atom on that end which is moving because it is vibrationally excited “strikes” the other molecule and the energy is transferred to kinetic energy. Think billiards.

]]>I think you have come to the same much the same conclusion as myself about the cloud emissivities.

I would put them in a range of 0.8,0.6,0.5,0.3.

I f we compare these figures with the Keihl, Trenberth paper we have;

1,1,0.6.

A glance tells you that these two sets are widely different.

The K-T numbers appear to be guesses.

However this paper features at the top of the IPCC case and I feel its just not good enough.

On computer models I have further concerns.

Equations and laws are used that are themselves not entirely reliable.

I think if you read the paper below on the robustness of Kirchhoff’s Law you will have some concerns.

At the end of the day only experiments will lead us to the physical processes underpinning the climate.

]]>Thank you for your reference and once again I will print it off and get back to you.

“tweaking the parameters to achieve some preconceived structure”. It would be more scientific to say “these assumptions are not valid because of this or this”

If we look at any reference to emissivity figures(even SODs) we quickly find that real figures are less than one.

There is a need for the utmost accuracy in trying to prove one way or another if AGW exists.

As Lindzen ha pointed out over the last weekend;

There has been a rise of about 0.7 degrees C over the last 150 years.

So any rounding up of the figures could give the impression that a problem existed when a more accurate figure might prove the opposite.

“About the Earth Surface Calculation: my amateur calculations show 15ºC is indeed the temperature that yields 390 W/m2 irradiation. Could you please ellaborate on your claim?”

Yes your calculation is correct and to get that figure you had to use the “perfect black body” figure of e=1.

Now use the same equation to find out what value of emissivity corresponds to the new revised figure of 396.1W/m2

]]>First of all, I’d like you to become aware of how closely you scrutinized this paper, and in contrast how easily you accepted the “engineer’s critique” (it’s so superficial you can’t even call it a “study” or “paper”, be it on the first or last year of a graduation). Attention is good, just use it when analysing contrarian claims as well.

About the cloud emissivity: he assumed two figures, one for low and another one for high cirrus. It’s an explicit assumption, and you’re right to question whether these are valid figures.

I found this reference about that, and figures seem to range from 0.4 to around 0.8 (although I don’t trust my own judgment on the subject. My knowledge is not enough to interpret it safely. There may be some missed underlying assumption that is relevant)

But the figures we were talking about were *clear sky* ones. So I would think cloud emissivity is irrelevant on this issue.

Then you do a quick digression on their motives “tweaking the parameters to achieve some preconceived structure”. It would be more scientific to say “these assumptions are not valid because of this or this”. Or you could show some other paper that finds something different with more plausible assumptions. But you did not do this. (oh, and again: cloud emissivity seems to be irrelevant to clear-sky figures)

About the Earth Surface Calculation: my amateur calculations show 15ºC is indeed the temperature that yields 390 W/m2 irradiation. Could you please ellaborate on your claim?

]]>I have now had a chance to read the paper reading by Kiehl and Trenberth.

On page 200 we find “The emissivity of low and middle level clouds is assumed to be 1.

..for high level clouds emissivity is set at 0.6″

Note these figures seem to be plucked out of (pardon the pun) ‘thin air’.

Instead of using real experiments this pair seem largely to be using computer models and tweaking the parameters to achieve some preconceived structure.

It is little wonder that none of these models stand up to any reality check.

On page 206 we have the famous diagram of the energy budget.

Notice that the values given are mostly given to three significant figures.

The figures in the diagram have since been revised and for example the Earth surface radiation now is given as 396.1 W/m2 that is to four significant figures.

Now any experimenter from an exact science will know that you should not claim any more accuracy in your final result than was used to calculate that result.

Which in the case of the diagram(page 206) should be to one significant figure.

The emissivity numbers I quoted above from the article are to one significant figure.

The other emissivity numbers I have seen are to two significant figures (Science od Doom examples).

This rule if applied makes the diagram unusably crude.

Yet that is the blunt reality of the situation.

This report would not be acceptable if presented in a first year physics lab.

One other problem with the Earth Surface Radiation figure when used in the Stefan Boltzmann equation for 15 degree Celsius temperature.

It gives an emissivity of well over one which is physically impossible.

]]>Thanks for the reference Ive printed it off.

I find it easier to read that way.

Bryan

I think it’s clearer now, thanks.

The difference made by man-enhanced atmospheric CO2 is just a few W/m2 (the difference, not the total backradiation). It is a known fact that CO2 is just the second place in the most important greenhouse gases, being H2O the first. Here’s a reference. Even so, changing the second-biggest GHG is not innocuous.

If I remember right, doubled CO2 forcing alone would raise global temperatures in 1ºC. The accepted overall sensitivty (i.e. including feedbacks) is calculated to be around 3ºC. So the direct role of CO2 is known to be a small part of the whole.

There’s a very extensive peer-reviewed literature about quantifying this sensitivity, starting in the late 19th century and continuing until today, through different lines of evidence, reaching similar results.

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