Mars Greenhouse

The question is poorly posed. Without CO2 there would be catastrophic and disastrous cooling. The amount of CO2 we have keeps us comfortable. Doubling the amount of CO2 will cause significant damage to our economy because it will change weather patterns.

The absorption lines of gases including CO2 are affected by both temperature and pressure. The higher the temperature and pressure the broader the lines. The temperature on Mars is 80C cooler than earth. The pressure is 0.7% of earth's atmospheric pressure. This means that the CO2 absorption lines are much narrower than those on earth. There is also very little water vapour.

This allows most of the radiation from Mars' surface to escape to space without being absobed by the CO2.



Without CO2 the planet would probably cool so much that the amount of water vapour will be significantly reduced also. So quite a lot of the 33C is attributable to the warming effects of CO2 plus the water vapour that can be held by the warmer atmosphere.



Close to its BB temperature. The greenhouse effect of the small amount of CO2 would, like on Mars now, be further reduced by the narrower spectral lines resulting from the reduced atmospheric pressure and temperature.

steve
> The question is poorly posed.
Hi Steve. I don't think the question is poorly posed at all. In fact Mars provides us an ideal "testbed" to investigate the hypothesis of CO2 warming. CO2 is the main ingredient in the Martian atmosphere (95%) and even though the atmosphere is much thinner than Earth's, CO2 is much more abundant (x 30) than on Earth. So it's ideally posed and controlled for a valid scientific analysis, because we don't have all those other gases and vapors (and nasty humanoids) mucking about, complicating the analysis.

My take on the data is that either the effective "radiative forcing" of CO2 (due to the so-called GH effect) is zero Or the "climate sensitivity" is zero. Meaning that any actual warming is neglible or that CO2, by itself, cannot "block" the warming from escaping. There are no oceans on Mars (which have enormous heat capacity on Earth) so the heat must be escaping into space. But the GH theory says that can't happen because the atmosphere is opaque to IR and so is "trapped" in the atmosphere.

That doesn't appear to be happening. Why? That is my question.

Personally, I confess that I expected to see some warming. Martian albedo is also somewhat lower, so I'm a little surprised by the NASA Fact Sheet claim that the Martian mean temp is the same as the black body temp. I would have expected 1C or so of warming, because of the relatively high concentration of CO2 compared to Earth. But for now, we'll assume the NASA data is correct.

The atmosphere of Earth is opaque to most EMR radiation. There are holes in the spectrum for _all_ visible light (hurray!) and some IR and RF to escape through. EVerything else is mostly blocked. (Good thing. The UV, x-rays and gamma rays would kill all life quickly)

There are 3 CO2 absorbtion bands around 2k-4k nm and a much wider band around 14k nm.


Note that water vapor is doing most of the 'heavy lifting' here.

You said:
"The absorption lines of gases including CO2 are affected by both temperature and pressure. The higher the temperature and pressure the broaden the lines."

I don't think this correct. Do you have a reference? The IR absorbtion depends on the frequency response of vibrating CO2 molecules. A single molecule can absorb an IR photon. The concept of pressure and temperature don't exist at this level. Is a water molecule "wet"?

www.wag.caltech.edu/home/jang/genchem/infrared.htm

I think you're conflating the apparent width of these lines with the resolution of the spectrum analyzer equipment. The same thing happens in radio receivers. Strong, nearby signals appear to have wider spectrum width than far-away signals, but the bandwidth of the signal is controlled entirely by the frequencies of the modulating audio signal. A pure RF carrier has zero bandwidth, theoretically, but it will look like it has bandwidth on your receiver, more or less, depending on the quality of the front-end electronics.

> Pressure broadening is a very general phenomenon
> of all spectral lines and involves a range of phenomena.

Ok, I'll accept that such "broadening" is observed. But it's not clear to me whether this is an artifact of observation induced by the resolving power of the equipment, or if it represents some fundamental phenomenology going on at the molecular level.

Putting it in simpler terms, a CO2 molecule is floating out there in the Martian atmosphere. An IR photon comes whizzing by, close to the 1.5k nm wavelength. The molecule whips out a barometer and says: "Sorry, I'm not going to capture you today, because the barometric pressure is too low for that. You're free to travel onward and upward to freedom!"

Is that how it works?

> One might question whether the data
> is precise enough to show a greenhouse effect that is small.

Then one might also question whether CO2 generates enough warming to cause concern in the environment, if it is going to take a powerful microscope to read the thermometer difference. Remember that CO2 is thirty times more abundant in the Martian atmosphere.

I suppose you'll say, well, we have to factor in a lot of other parameters, water vapor, oceans, clouds, methane etc.

Then I'll have to call "BS"! All along the CAGW alarmists have been shouting, it's the CO2! It's the CO2! We're all going to die, unless we reduce the CO2 concentrations!

Where's the warming? We have the ideal lab, in Mars, to prove this CO2 warming phenomenon for the world to see and learn.

<soapbox>
It's starting to resemble that old fairy tale about "Stone Soup". Some swindling panhandlers conned the villagers to give them meat, veggies and seasonings to add to their "magic" recipe consisting of stones and water.

In this case, the stones are made of CO2, and the panhandlers are the economic fascists (sorry, that's the best term to describe this kind of totalitarian economic-political behavior) are trying to con us out of our taxes and freedom to conduct our manufacturing enterprises to make an honest profit for the benefit and security of everyone.
[Edit: ... and if you think I'm exaggerating about the 'totalitarian' aspect of this campaign, check out these WUWT articles:
wattsupwiththat.com/2010/11/11/germany-gets-ugly-with-skeptics/
wattsupwiththat.com/2010/11/20/surreality-carb-contemplating-a-skeptical-science-regulation-with-penalties/]
</soapbox>

> While a molecule is in the process of colliding with
> another molecule its absorption spectrum will shift.

Can you cite some research detailing this phenomenon at the molecular level? Not at the instrument level where we're dealing with lumped sums of process and observational noise. Show me the formula that calculates how much the spectrum shifts when the molecule is bumped. I'm not denying this happens, I just want to see the science behind it.

> To compare with Mars it would be useful to know what the
> theoretical impact of the CO2 is before we decide whether the
> apparent lack of evidence for a greenhouse effect is interesting.

We're in agreement on that one. :-]


> Only in the imaginary world where we are totally reliant
> on fossil fuels.

Uh, that would be pretty close to the world we're living in right now.

Yes, the Chinese are selling a lot of solar and wind technology to us right now, but using little of it themselves. Guess what keeps their home fires burning? This 'cap and trade' nonsense is going to make a significant dent in U.S. industrial and commercial output. The Russians and Chinese are exploiting every bit of this (and are undoubtedly helping to pull the strings behind the curtain).

And try getting Obama and his gang to start building nuclear power (the most sensible solution). He makes "lip service" sounds once in a while to appease the "angry mobs". But his wacko-leftist base would never go along with actually building these today.

Oh, I forgot to insert the <soapbox> brackets. Sorry. :-|

> My knowledge of it comes from my university courses -
> so I don't have specific references. If you Google
> "pressure broadening" or "impact pressure broadening"
> you should find references for further reading.

Darn, where are the experts when you need them! What you've asserted amounts to a kind of "Compton Effect" for molecules. At the atomic level, it's well studied and involves x-ray and gamma spectral shifts.

At the molecular level it would be at a lower set of frequencies, maybe thermal? This all kind of "makes sense", what I need to see is the proof of the existence theorem for this "effect". I'm a little skeptical because thermal photons won't have much energy, just a few electron volts. (Compared to 50Kev or higher for the real Compton Effect). So even if the shift exists, it would probably be hard to detect and wouldn't have much effect on heat exchanges (thinking out loud here).

Leif Svalgaard, are you listening to this discussion? Can you tell us more about this "thermal Compton effect"?

Thanks,
John/af4ex

The Compton effect relates to the scattering of photons by (usually) electrons rather than to the absorption of photons by molecules. The energy of the scattered photon (assuming the electron is relatively low energy compared with the gamma ray) is a function of the original energy and the angle of scatter - analogous to snooker/pool balls colliding (due to the requirement to conserve both energy and momentum) and not really analogous to pressure broadening.