Greenhouse Effect om Mars - Page 3

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Extra Sense


Posts: 1471

Reply: 41



PostPosted: June 16, 2005 5:46 PM 

Rocks,

you must take a name They're Runaway Rocks

It must be obvious even to a lawyer, that 10 molecules is a small number compared to many Gigatons of Martian atmosphere. You are getting laughable by a minute

e Laughing s

They're Rocks


Posts: no

Reply: 42



PostPosted: June 16, 2005 6:05 PM 

You are a complete idiot.

If you had basic reading comprehension skills, you would have noticed that I stipulated that such a scenario was not actually possible, but an idealization meant to illustrate a point -- that the impact of greenhouse-inducing molecules will be attenuated by increasing separation from one another, thus making the fact that Mars's atmosphere is only one percent as thick as earth's entirely relevant to the discussion of the greenhouse impact on Mars. Now go play with your Martian concrete, silly boy.

Martin Gradwell


Posts: 323

Reply: 43



PostPosted: June 16, 2005 6:09 PM 

Re: reply 33. Daniel, can you point me at any of the sources which cite a greenhouse effect "raising temps by 5-10 degrees c"? I know lots of sites which say the greenhouse effect on Mars is "small", but none which quantify it, presumably because they couldn't do so without destroying their own case.

Can you find any flaw in my maths? If not, it trumps any number of unsupported assertions. I hate it when people won't believe what I say unless I can prove that someone else said it first. It means that anything original that I say will never be believed (and anything I say which is totally wrong will be believed anyway, provided I can remember which site I filched it from). That's why I'm "against the mainstream", because it epitomises the "if it's original it can't be right" mindset. Not that I'm saying I'm the first person ever to notice that there's significant global warming on Mars, obviously ES on the face of it has a claim to priority here, I just don't see why it matters whether other people have said it before or not.

Re: reply 38. for "CO2 atoms" read CO2 molecules.

Re: reply 39-40, TR, did you read my reply 38?

You can reduce the thickness of an atmosphere, and reduce it, and reduce it, until you have removed everything except the greenhouse gases. This has no effect on the greenhouse properties of the atmosphere. Even when you have reached that point where there is nothing left except greenhouse gases, you can continue to attenuate the atmosphere, provided you replace the CO2 with CFCs. You can have an atmosphere so attenuated that it wouldn't register on the vast majority of Earth's barometers. It could be almost a vacuum and still have just as much greenhouse effect as Earth's atmosphere. Of course, when there's nothing left except the most effective greenhouse gas in the universe, you can't remove any more without having an effect on the greenhouse properties of the atmosphere. At this point, you are dealing with a pretty thin atmosphere, and the thinner it gets the less greenhouse effect it will have. But even in this most extreme case it doesn't lack greenhouse effect because it is a thin atmosphere. It lacks greenhouse effect because it doesn't contain enough CFCs or whatever. The thinness is accidental. It is a consequence of your insistence that the atmosphere should contain nothing but greenhouse gases. Take away that arbitrary insistence, and the atmosphere can be as thick as you like.

Extra Sense


Posts: 1471

Reply: 44



PostPosted: June 16, 2005 6:18 PM 

Rocks,

You are banned from this forum for foul language and mental development disability

e Wink s

RedSky


Posts: no

Reply: 45



PostPosted: June 16, 2005 6:24 PM 

I just want to add my 2 cents as a meteorologist.

Mars' CO2 probably does have some effect on its temperature, but not much because it is so thin. But the issue is that Mars' atmosphere has more than likely been stable for quite a while. Thus, whatever the greenhouse effect, Mars temperature has already reached equilibrium long ago. (not including factors coming together to change its climate overall like combinations of orbital eccentricity, polar axis precession and nutation).

I think the misunderstanding is that a "runaway" greenhouse will continue to some extreme temperature. It will reach equilibrium, then stop. Venus hasn't vaporized, nor will Earth or Mars. (well, at least until the sun goes Red Giant).

The issue/ concern with earth and the greenhouse effect is that *changing* (increasing) the CO2 concentration will cause an increase in temperature to a new (higher) equilibrium temperature. Even if that change is only 5 C, that might have large consequences for earth's climate (expansion of desert areas, melting of polar ice, etc).

RedSky

They're Rocks


Posts: no

Reply: 46



PostPosted: June 16, 2005 6:28 PM 

Well, yes, Martin, it lacks greenhouse effect because it doesn't contain enough CFCs or whatever, which is just another way of saying it lacks effect because it is thin.


So, I'm not sure where we're in disagreement here. Let's remember the topic of this thread. BS tried to construct a reductio ad absurdum of the argument to runaway greenhouse. He tried to show that, because Mars is 95 percent CO2, we should be led to the logical conclusion that it should be very hot due to a runaway greenhouse. Obviously, he was trying to make the point, via this reductio, that because Mars is cold rather than hot, we can stop worrying about runaway greenhouse.

But, the Martian atmosphere is one percent the thickness of earth's. My basic point, which I don't see how you have refuted, if you think you have, is that at one percent thickness, the greenhouse-causing molecules, though dominant in the atmosphere, will be greatly attenuated relative to their companion molecules on earth; and hence their ability to trap heat on Mars will be greatly diminished. And thus BS's stupid reductio fails.

They're Rocks


Posts: no

Reply: 47



PostPosted: June 16, 2005 6:31 PM 

Well, thanks RedSky. It keeps mystifying me how Martin can dismiss thinness of atmosphere as consequential for greenhouse effects, though it remains possible I have missed his point. And thanks for the clarifications of equilibrium.

OMG


Posts: no

Reply: 48



PostPosted: June 16, 2005 7:23 PM 

Wait wait wait, just because ES doesn't understand the basics of how the greenhouse effect would have to work doesn't mean that the rounded rock ISN'T Martian concrete. How dare you.

Extra Sense


Posts: 1471

Reply: 49



PostPosted: June 16, 2005 7:29 PM 

RedSky,

I have never heared word "runaway" being used to describe anything natural Very Happy You are certainly right about stable eventual temperature dynamics, that depends on the level of CO2.

The thing is, that level of CO2 depends on the CO2 influx, and on the CO2 consumption, on Earth most importently by the forests.

e Razz s

Extra Sense


Posts: 1471

Reply: 50



PostPosted: June 16, 2005 7:31 PM 

OMG,

Are you a lawyer too?

e Laughing s

Martin Gradwell


Posts: 323

Reply: 51



PostPosted: June 16, 2005 7:51 PM 

re: reply 45.
Hi redsky.

"Mars' CO2 probably does have some effect on its temperature, but not much because it is so thin."

I believe that you are mistaken on this point, for reasons I have already given. First of all, the Martian atmosphere may be thin, but the fact that it is 95% CO2 means that it contains a lot more CO2 than Earth's much denser atmosphere (26 times as much or thereabouts for a vertical column of equal cross-section). Even taking into account other greenhouse gases such as H2O and CH4, it still has more greenhouse effect than Earth's atmosphere. This is borne out by the observed temperatures on Mars, which are considerably higher than what would be observed with no greenhouse effect, or with only Earth levels of greenhouse effect.

"I think the misunderstanding is that a "runaway" greenhouse will continue to some extreme temperature."

Certainly there are people who are of that opinion, as a quick google search will demonstrate. However, I am not certain that anyone contributing to this thread is of that opinion. I myself am willing to keep an open mind on the possibility, with regard to the Earth, since I don't have a sufficient understanding of the processes controlling unprecedented extremes of weather to be able to rule it out. I accept, though, that you say about equilibrium makes sense. The fact that life has persisted for billions of years suggests that the climate system is pretty stable within very broad limits, but every system will break if you mess with it enough. Some will break in a spectacular fashion. I hope that this is not the case with our climate.

ES, as far as I can tell, accepts the reality of global warming but is anti-Kyoto because he believes that addressing deforestation is a more urgent priority, and that if deforestation isn't addressed then no amount of regulation of CO2 emissions will help. I think that there has to be both, and that third world countries will be reluctant both to reduce emissions and to address deforestation issues if the developed nations aren't seen to be taking on their share of the burden.

Re: reply 46.
TR says
"Well, yes, Martin, it lacks greenhouse effect because it doesn't contain enough CFCs or whatever, which is just another way of saying it lacks effect because it is thin."

No it isn't. If I say that Earth's atmosphere doesn't contain enough CFCs that isn't the same as saying that the Earth's atmosphere is thin. They are two completely different statements. Even in the extreme case of a thin atmosphere containing only CFCs, the two statements are not equivalent because there's nothing stopping you from adding non-greenhouse gases into the mix. I'm running out of ways of saying this.

"My basic point, which I don't see how you have refuted, if you think you have, is that at one percent thickness, the greenhouse-causing molecules, though dominant in the atmosphere, will be greatly attenuated relative to their companion molecules on earth"

If those companion molecules are not greenhouse gases then they are irrelevant. They might be relevant to a discussion of convection, but not of the greenhouse effect. On the other hand if by companion molecules you mean the nearest neigboring molecules of greenhouse gas, then those companion molecules are closer together in the Martian atmosphere than they are in Earth's atmosphere. They are not attenuated relative to their companion molecules on earth.

They're Rocks


Posts: no

Reply: 52



PostPosted: June 16, 2005 8:38 PM 

Martin, now I think we are talking about the same thing. Before it seemed to me you were saying that the Mars atmosphere was thinner in terms of CO2 but that this didn't matter, because of the greater relative amount of CO2. Now you are saying the CO2 molecules are closer together than their like molecules on earth. How do you know this? Just because the level of CO2 in the Martian atmosphere is greater than on earth, it does not follow that their concentration or proximity is greater -- indeed how could they be, if the atmosphere overall is one percent as thick as earth's? We need some cites. Maybe RedSky can contribute some info.

Martin Gradwell


Posts: 323

Reply: 53



PostPosted: June 16, 2005 8:54 PM 

CO2 molecules on Mars are closer together than their like molecules on earth because CO2 is only about 370 parts per million of the Earth atmosphere. That's not a lot. See reply 17 for more details.

Raptor Witness


Posts: 2255

Reply: 54



PostPosted: June 16, 2005 9:11 PM 

There's an equilibrium of some kind going on also, isn't there? Didn't someone say that the surface temperature and pressure are close to the triple point?

They're Rocks


Posts: no

Reply: 55



PostPosted: June 16, 2005 9:14 PM 

But Martin, as you pointed out, CO2 is not the only cause of heat-trapping. Moreover, even though there is a much greater percentage of CO2 in the Martian atmosphere than in earth's, since the atmosphere of Mars is much, much thinner, I don't see it follows that those greenhouse-causing molecules are necessarily closer together; and it certainly doesn't follow that they are closer together in such a way as to create a greenhouse phenomenon such as can be accounted for on earth not just by CO2 but also by water vapor and other factors.

It doesn't even follow, it seems to me, that there is more CO2 on Mars than on earth. If Mars's atmosphere is one percent that of earth, then the absolute amount of CO2 there could still be lower than the absolute amount here.

In any event, maybe RedSky can clear this up, and specifically show how the atmospheric thinness reduces greenhouse influences. For that is the claim, from various sources, that you are questioning.

Martin Gradwell


Posts: 323

Reply: 56



PostPosted: June 16, 2005 10:04 PM 

TR, there's a very simple relationship between atmospheric pressure and the weight of the gas in the atmosphere. The pressure of air pressing down on one square foot of ground, say, is simply the weight of the column of air directly above that square foot. Imagine a column, one square foot in cross section, extending from the ground all the way up into space.

Of course air doesn't press directly downwards. It presses in all directions. But the left->right pressure exactly balances the right->left pressure and they cancel out unless there is a wind. The same is true for any lateral pressure.

If we measure pressure in millibars (where 1 bar = the Earth's atmospheric pressure at sea level) then as I said in reply 17 about atmospheric CO2 "In terms of its contribution to atmospheric pressure, that's about 0.37 millibars. The pressure of CO2 on Mars is 95% of 10 millibars i.e. about 9.5 millibars. That's about 26 times as much as on Earth"

That means that a column of air on Mars will contain about 26 times as much CO2 by weight as a similar column on Earth.

There are two complicating factors. First, notice that I said "by weight", not "by mass". Gravity on Mars is about a third of what it is on Earth. You need three times as many molecules to get the same weight. So to get the relative numbers of molecules I should multiply the Mars figure by three. A column of air on Mars will contain about 26*3 = 78 times as many CO2 molecules as a similar column on Earth. But the other complication is that again because of the lower gravity the atmosphere on Mars will extend three times further out into space. When measuring the density in terms of molecules per unit volume these effects cancel out. I tried to avoid these complications before because it was tricky enough getting the point across without them. But I hope you will see now that however you work it out, whether by weight or mass or numbers of molecules, there's a lot more CO2 on Mars than there is on Earth, and it's a lot denser.

They're Rocks


Posts: no

Reply: 57



PostPosted: June 16, 2005 11:31 PM 

Martin, I appreciate you taking the time to explain this, but somewhere there is a flaw, either in your reasoning or in the reasoning of every source I have been able to come up with. They all say the same thing: that the density of the greenhouse gases on Mars is much less than on earth, and this is the reason there is no significant greenhouse effect. Maybe you could tell me, then, that if there is a lot more CO2 on Mars, and if these gasses are a lot denser there than here, what it means when we say that the Martian atmosphere is one percent that of earth?

Here is a link, very typical of what I have found:

http://www.earthsky.com/scienceqs/browsefaq.php?c=752241f8d7&f=379

From he linked material:

The greenhouse effect is created when gases like CO2, ozone, and water vapor trap solar trap heat that strikes a planet's surface. It's a lot like when a pane of glass traps heat inside a greenhouse. On Mars, this greenhouse is relatively flimsy. That's because the atmospheric pressure on Mars -- the density of the gases -- is very low. Mars' atmosphere is mostly carbon dioxide, but this martian air is so thin that there's no significant greenhouse warming.
Doug Ellison


Posts: 1077

Reply: 58



PostPosted: June 17, 2005 7:01 AM 

Perhaps the fact that the ammount of solar radiation at Mars is less than half that on Earth is a contributing factor?


Doug

Daniel


Posts: 991

Reply: 59



PostPosted: June 17, 2005 8:16 AM 

I would like to add here, that something being overlooked is that a lot of the "greenhouse" on Earth comes from clouds. Earth has a pretty high level of cloud cover - our clouds trap a LOT of heat, compared to normal atmosphere.

Lacking clouds for the most part, Mars is missing out on a lot of warming that Earth gets - with one BIG exception - the global dust storms. I remember reading that average temps on Mars shot up 40-50 degrees C when it was covered in the last global dust storm.

Daniel


Posts: 991

Reply: 60



PostPosted: June 17, 2005 8:19 AM 

Martin,
You very well could be right, but almost all of the "expert" sites on Mars (such as the Mars climate site for NASA) throw around this 5-10 degree figure... and I can't find the math or the explanation of the model they use to achieve it...I'm not really looking for an explanation of why you are right - really, I'd like to see their explanation, and then an explanation of why they are wrong...

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