Greenhouse Effect om Mars - Page 5

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They're Rocks


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Reply: 81



PostPosted: June 19, 2005 11:46 AM 

I'll return to this discussion later. I do think RedSky could be of some help in answering the various questions, if someone would like to alert him. In the meantime, ES, I wouldn't be parading your threads, If I were you.

Martin Gradwell


Posts: 323

Reply: 82



PostPosted: June 19, 2005 4:40 PM 

Okay, I'm making progress. In reply 23 I wrote "Other things being equal albedo-wise and greenhouse-wise, the temperature on Mars would be about 44% of the temperature on Earth."

But that's not right. The *power* (measured in gigswatts or terawatts or whatever) of the black body radiation from Mars would be 44% of the power of the black body radiation from Earth. But temperature is proportional to the fourth root of power, apparently (for reasons which I may have known once, but it's a long time since I studied anything like this).

The fourth root of .44 is .81, near enough. So in the circumstances described we should actually expect the temperature on Mars to be about 81% of Earth's.

Repeating the steps in reply 23 with the corrected percentage plugged in,

The mean temperature on Earth is 15 C according to
http://library.thinkquest.org/C005921/Earth/earth.htm
and that's 288 degrees K (to convert from C to K just add 273).

81% of 288 is 233 degrees K. That's minus 40 degrees C. The actual average temperature on Mars is -63 degrees C according to
http://library.thinkquest.org/C005921/Mars/marsSurf.htm

So Mars is actually 23 degrees colder on average than it would be if it had the same albedo and greenhouse effect as on Earth. The question now is *why*.

At this point it would help to know if Mars albedo is really about the same as Earth's. The wikipedia article on albedo tells us "Earth has an average albedo of 37-39%". The article on Mars tells us it has an albedo of 0.15. Or 15% to put it in the same terms as the Earth figure. This means Mars is much less reflective than the Earth. It actually absorbs 85% of the light that hits it, as opposed to 61..63% for the Earth. This should make Mars warmer than it actually is - I won't bother with quantifying the difference. It's sufficient to note that it should make Mars warmer, not colder.

If Mars is colder than it would be with the same albedo and greenhouse effect as Earth, and albedo isn't the culprit, then it seems that greenhouse effect must be the culprit. There must indeed be less greenhouse effect on Mars than there is on Earth.

But again the question is why. Because the air is thinner there? But all the descriptions I've seen of the greenhouse effect say it depends on the quantity of greenhouse gas in the atmosphere, not on the overall thickness of the atmosphere. I have yet to see a description of the role of the non-greenhouse atmospheric gases, and why they are necessary for a robust greenhouse effect. We still need that elusive better description of the greenhouse effect.

Daniel


Posts: 991

Reply: 83



PostPosted: June 20, 2005 8:32 AM 

Hi Martin,
There are plenty of sites that explain the Greenhouse effect properly - CO2 is opaque on the IR wavelengths, and thus absorbs more IR Radiation than the surrounding molecules. This heat is then transferred back to the ground via conduction (or convection - which is a type of conduction).

Apparently, the reason that the conduction/convection isn't mentioned in this type of literature, is because that is a seperate discussion entirely on how atmospheres work. The Greenhouse gases are just adding a little heat on top of the heat already in the atmosphere. But that relative small amount of heat energy is enough to lift up the average temperature of the whole system, on top of the heat the atmosphere gains from the surface from direct conduction - which apparently is a lot bigger than the "greenhouse" contribution.

But, as you asked, here is a website that does a good job spelling out the need for atmospheric conduction or convection (plus direct radiation) to heat the ground, once the heat is captured by greenhouse gasses:

[link]

Martin Gradwell


Posts: 323

Reply: 84



PostPosted: June 21, 2005 2:58 PM 

Re: reply 83. Daniel, the link you give is a good one, but it's the same one that I gave in reply 74. And as I pointed out there

'The budget diagrams seem to suggest that the heat flow due to conduction/convection is actually the other way, that "sensible heat flux" (conduction and dry convection), and "latent heat flux" (phase changes of water) take heat away from the ground and into the atmosphere.'

If you look at the "Addition of Energy Transfers via Conduction and Convection between Earth's Surface and Atmosphere" diagram on that page you will see that there is a net flow due to conduction/convection from the ground to the atmosphere of 30 units - that's 6 "sensible heat flux" + 24 "latent heat flux". Conduction/convection doesn't warm the ground, it cools it down.

You can say that without the greenhouse effect the atmosphere would be cooler and therefore these fluxes would be larger. I think that's what you saying, and it does make sense. Except - if the non-greenhouse gases which are almost entirely responsible for the sensible flux were to be completely removed from the atmosphere, then the sensible flux would reduce almost to zero.

If we were to remove all the gases from Earth's atmosphere except greenhouse gases, then I see no indication that this would greatly affect the radiative heat flows. But it would almost remove the "sensible heat flux" from the equation. There'd still be cunduction/convection in the remaining greenhouse gases, but it would be tiny compared to what you'd get in a thick atmosphere. So, a major source of cooling for the ground would be eliminated. The ground should be hotter, other things being equal.

We still need to take into account the latent heat flux, and the complication here is that you can't remove that effect without removing water vapour from the air, and water vapour is a greenhouse gas. But, suppose we removed the water from the earth in order to prevent phase changes. This would remove water vapour from the atmosphere, but we could make up for that by inserting an equivalent quantity of some other greenhouse gas into the atmosphere. We would then have an atmosphere with as much radiative greenhouse effect as it currently has, minuscule sensible heat flux and zero latent heat flux. The ground would be a lot warmer than it currently is - and that's *before* we take into account that the lack of clouds would reduce the Earth's albedo considerably.

So it looks like an Earth with no water and a Mars-type atmosphere - thin but loaded with CO2 - would have a warmer surface than it currently has. The elimination of latent heat flux, the near-elimination of sensible heat flux and the significant reduction in albedo would all conspire to have that effect.

Unless I'm still missing something.

Daniel


Posts: 991

Reply: 85



PostPosted: June 21, 2005 4:04 PM 

Martin, you are really really really missing something.

That heat transfer from ground to atmosphere isn't cooling the Earth - its warming it. Without the atmosphere, the heat would radiate away - but with no way of returning. The atmosphere provides a mechanism for some of that heat to be returned to the surface - via convection/conduction.

Let me simplify. Without any greenhouse gasses, so just a pure N/O2 atmosphere, the Earth's atmosphere would still warm the surface. Why? Because heat radiated or conducted from the surface into the atmosphere is partially conducted back. This makes the atmosphere a heat source for surface temperature. Sure this heat is "stolen" from the surface - but without the atmosphere it would be lost anyway - but without a mechanism to capture a portion of it.

What the greenhouse gases are doing, are adding more energy into the atmosphere - so now the atmosphere is not just capturing some of the lost heat and returning it thanks to convection - but by radiation capture as well. So that means there is more energy in the atmosphere to be returned to the surface.

Mars's atmosphere transplanted to Earth would result in a low amount of greenhouse warming because it is a poor conductor of heat.

Greenhouse warming in the atmosphere is not just a process of capturing heat. Its also a process of getting that heat back to the surface. And that is where atmospheric density matters. Low density (Martian) atmospheres just can't get that heat back as well, because it is a poor conductor - and don't have strong convection.

Daniel


Posts: 991

Reply: 86



PostPosted: June 21, 2005 4:30 PM 

*sigh* Ignore what I wrote above. I dig into the subject more, and find that these watered down pages are confusing things more - not clarifying. Apparently, according to some better pages I found, we are both right... and wrong. Again.

Here is a link to the two technical pages I found helpful - I think these watered down pages we were reading just confused things. The first is a good overview - the second is a definitive answer that we both have a lousy understanding of how the greenhouse effect works. I think you'll find them helpful.

www.du.edu/~etuttle/weather/atmrad.htm
www.copernicus.org/EGU/acp/acpd/2/289/acpd-2-289_p.pdf

The bottom line - atmospheric density is important. But the Greenhouse gasses are even more important (though If I'm reading this right its more effective in denser atmospheres with multiple layers). They also state that H20, not CO2 is the primary greenhouse engine. So this fixation on CO2 is mainly because we can affect it, not because its the main greenhouse contributor.

Extra Sense


Posts: 1471

Reply: 87



PostPosted: June 21, 2005 5:12 PM 

--- this fixation on CO2 is mainly because we can affect it ---

We actually can not, by the suggested changing of fossil fuel pollution. Kyoto and the rest of it is simply stinky communist hoax, a make believe sham.

e Cool s

Daniel


Posts: 991

Reply: 88



PostPosted: June 21, 2005 7:52 PM 

Right... because there's no way taking carbon out of the ground and releasing it through artificial processes could have a noticeable affect on atmospheric CO2 content... Rolling Eyes

OMG


Posts: no

Reply: 89



PostPosted: June 21, 2005 8:05 PM 

One thing people always seem to ignore in the entire 'global warming' debate is that we are taking materials out of the ground and BURNING THEM to create energy. This by itself must warm the Earth more than it would otherwise.

Extra Sense


Posts: 1471

Reply: 90



PostPosted: June 22, 2005 5:31 AM 

OMG,

Good point. A realistic model is needed, but the issue is too politicized and has had attracted too much pseudoscience.


It occured to me, that using agro-produced etanol as a fuel might be a great CO2 reducer, along with timber industry!

They take CO2 from the air Razz

e Razz s

Extra Sense


Posts: 1471

Reply: 91



PostPosted: June 22, 2005 5:45 AM 


http://www.ethanol.org/PressReleasec5.6.05.htm

e Cool s

Extra Sense


Posts: 1471

Reply: 92



PostPosted: June 28, 2005 7:49 AM 

Dust falls down on Mars 7 times faster than on Earth, and is the most unlikely to produce even coloring of the Martian atmosphere, which is being observed.

Velocity = C * sqrt( Weight/AirDensity )
where coefficient C depends on the shape of a particle.
The same particle on Mars will have half the Weight, a a hundred times lower AirDensity compared with Earth.
Which means its falling Velocity will be sqrt(50) =~ 7 times higher.
[link]
Velocity = C * sqrt( Weight/AirDensity )
where coefficient C depends on the shape of a particle.
The same particle on Mars will have half the Weight, a a hundred times lower AirDensity compared with Earth.
Which means its falling Velocity will be sqrt(50) =~ 7 times higher.
[link]

The reason that Martian sky can be seen with reddish color, is that often the infrared is bundled with red, and then it is displayed as red.

The infrared color of Martian sky, it is due to greehouse effect caused by the CO2 atmosphere.

e Razz s

Andy G


Posts: 227

Reply: 93



PostPosted: June 28, 2005 10:48 AM 

ES, this is just a cheap troll. Or else you're dangerously scientifically illiterate.

You've given us an equation for terminal velocity which (if you put in more accurate units than yours) suggest that the terminal velocity is nearer 4.8 times higher than on Earth, assuming the particles are the same size, shape and density. (But this doesn't tell us what that speed is, for dust-sized particles...)

Then you seem to suggest that this somehow automagically means that the Martian atmosphere has no dust in it, and the red colour of the atmosphere is due to IR from the greenhouse effect.

:-|

I visited your website today. I suggest if you are desperate to continue to use the name "Extra Sense" you might like to check out the dictionary for a definition of "oxymoron", first.

Andy G

Extra Sense


Posts: 1471

Reply: 94



PostPosted: June 28, 2005 11:36 AM 

AndyG,

You believe all the crap you read in newspapers, and disbelieve any reasonable argument of mine.

It is the high time to get real, baby


e Razz s

Daniel


Posts: 991

Reply: 95



PostPosted: June 28, 2005 12:03 PM 

It is the high time to get real, baby

Wow - does that mean you're going to admit that all those video's and pictures of Antarctica I posted aren't fake?

Extra Sense


Posts: 1471

Reply: 96



PostPosted: June 28, 2005 12:27 PM 

Daniel,

it is not good, that fixation of yours; better to agree to diagree.

Move on to the new topics

e Cool s

Daniel


Posts: 991

Reply: 97



PostPosted: June 28, 2005 1:08 PM 

Just illustrating your ideas of "open minded" and "getting real".

Andy G


Posts: 227

Reply: 98



PostPosted: June 29, 2005 10:29 AM 

Hi all! Here's a stab at a reasonable solar input/output chart for Mars, taken from the Earth one that appeared quoted in a recent reply.


The figures in red are my Mars guesses. The input is 147Wm/2 - that's a diurnal average over the Martian equator, like the figure of 342 for Earth. I've decreased it to 43% to due the distance.

There's hardly any clouds, so reflectivity from these is low. The given albedo is 0.15, on the 147 input, so set to be about 22. Thermals and evapotranspiration are guesses, but low (not much atmosphere, not much water vapour). Indeed the atmos holds very little energy in total - something to think about when considering greenhouse stuff. Much of the surface temp is re-radiated through the atmosphere, but there is a greenhouse effected back-radiation (I've made this 1% of Earth's, due to the 1% of Earth's atmosphere density on Mars. Yes, I know it's CO2 rich there, but it's not dense, there's no water vapour and no blanketing cloud coverage. Thin atmospheres physically can't store much latent heat, and have little to give back. (Witness the range of temp over diurnal figures for Viking, for example.)

Right...now I need to find a reasonable figure for the /real/ Mars outgoing IR signal that comes close to my guessed 124 W/sq m.

Any opinions welcome!

Andy

Gingle Blingle Stoogleplex


Posts: 93

Reply: 99



PostPosted: June 29, 2005 11:40 AM 

It's obvious to anyone that Mars is in fact hotter than the mythical Hades itself. The temperature is so high that it is distorting all measurements ever taken of it.

Therefore there is clearly some other force at work preventing our rovers and probes from melting under this intense heat, and this MUST BE STUDIED.

And yet NASA ignores all this incontrovertible proof. What do they have to hide? Perhaps they are in league with Hades?

Extra Sense


Posts: 1471

Reply: 100



PostPosted: June 29, 2005 12:29 PM 

Andy,

--- know it's CO2 rich there, but it's not dense ---

The CO2 on Mars density is 30 times higher, than on Earth. I think, you must review you figures to reflect that fact.

ES

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