Greenhouse Effect om Mars - Page 4

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Hynee


Posts: 200

Reply: 61



PostPosted: June 17, 2005 10:39 AM 

I think Extra Nonsense has it in one. Mars is a boiling hot place, thus the rovers could not possible survive on its surface, thus all the pictures we are seeing must have been faked, thus all the rocks are artificial. Problem solved.

On a more serious note, you could probably post this in the open forum. CO2 heats up a place because it is clear in visible light, but black in IR, and given earth has 1 atm @ 365ppm, Mars 0.01atm @ 950000ppm, that's about 25 times the CO2. I think the reason that it doesn't retain the heat is because it radiates it away.
Maybe someone else said that earlier, I didn't read the whole thing. I don't know that much about atmospheres either.

They're Rocks


Posts: no

Reply: 62



PostPosted: June 17, 2005 12:16 PM 

I think that point is that, even if Mars has 25 times the amount of carbon dioxide than earth, that this CO2 is less dense -- the atmospheric pressure at ground level on Mars is 1/100th that of earth. Thus, the attenuated C02 is not effective at trapping heat.

Martin, all the literature I have found agrees with this. At this point, I think it's incumbent on you to show why this literature is wrong and your differing analysis correct.

Martin Gradwell


Posts: 323

Reply: 63



PostPosted: June 17, 2005 1:30 PM 

Re: reply 57. TR says "somewhere there is a flaw, either in your reasoning or in the reasoning of every source I have been able to come up with".

Indeed there is. You have hit the nail on the head.

There are tens of thousands of sites describing Martian global warming, or more accurately the supposed lack thereof, and I have only been able to view a small fraction, but those I have viewed are exactly as you describe.

E.g. Googling 'Mars "greenhouse effect"' we get "approximately 55,600" hits. The first two hits are about terraforming. "Researchers say the best way to make Mars habitable would be to inject synthetic greenhouse gases into its atmosphere". #3 is the ESA saying "The Red Planet displays hardly any greenhouse effect. Mars does have some atmospheric carbon dioxide, but almost no atmosphere!" #4 is this very discussion (well done google!) but you'll have to search a long way down the list for anything comparable. I haven't found nything comparable. #5 is Astronomy 104 Lecture 17 "Why doesn't Mars have a greenhouse effect now? Atmosphere too thin". And so on, for page after page. The link you gave is indeed typical. Despite extensive searching I have found only two places apart from this thread which actually give a figure for Mars greenhouse effect

[link]
"Mars has an atmosphere that's mostly carbon dioxide. This creates a greenhouse effect, but because the atmosphere is so thin, the resulting increase in global temperature is only about 5 to 10 degrees. Overall, Mars is much colder than Earth."

and

[link] (and mirrors thereof)
"Mars' thin atmosphere produces a greenhouse effect but it is only enough to raise the surface temperature by 5 degrees (K); much less than what we see on Venus and Earth.

I have yet to discover a calculation justifying either these numerical claims or the ubiquitous claims that the greenhouse effect on Mars is negligible or nonexistent.

The thing is, terraformers want you to believe that Mars could easily be made habitable by introducing a greenhouse effect. The notion that there might already be a strong greenhouse effect doesn't help their cause at all. Conversely, people who want you to believe that Mars is long dead and will always be a frozen barren wasteland don't particularly want you to know that the daytime temperature can reach 20 C. On both sides of the divide, a current greenhouse effect is an embarassment which can be plausibly be denied (if you avoid all calculations) or, better still, can be safely ignored.


"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?"

Certainly. It means that the atmospheric pressure on Mars is one percent of the atmospheric pressure on Earth. That is, the weight of a column of Martian air pressing down on the Martian surface below it is one percent of the weight of a similarly proportioned column of Earth's atmosphere on Earth (with the column extending all the way from the ground into space). Which means (taking into account the 1/3rd gravity on Mars) that the mass of the Martian air column is about 3 percent of the mass of the Earth column.

But greenhouse gases in the Earth atmosphere are trace components. They are measured in parts per million or, in the case of nitrous oxide or CFCs, in parts per billion. You don't need an atmosphere as thick as the Earth's to have a lot of greenhouse gas producing a strong greenhouse effect.

Re: reply 58: Doug Ellison says "Perhaps the fact that the ammount of solar radiation at Mars is less than half that on Earth is a contributing factor?"

Indeed it has a lot to do with the fact that Mars is, for the most part, colder than Earth. But it has no bearing on the presence or the supposed absence of a greenhouse effect there.

Re: reply 59. Daniel, The main effect of clouds is to reflect a lot of the sunlight hitting the earth back into space. That is why you will find that the hottest summer days are usually the ones when there is very little cloud. Sometimes we do get lucky, when clouds form in late evening and have dispersed by morning, so they keep heat in overnight without reflecting sunlight away during the day. But most of the time clouds have a cooling effect. Transparent water vapour is another matter, but it is by no means certain how much of Earth's greenhouse effect is caused by water vapour.

Re: reply 60, Daniel, can you give me the URL for the "Mars climate site for NASA? Thanks.

Re: reply 61. Hynee, the claim being made is that there is a strong greenhouse effect on Mars. If we can't find a single webpage outside of this thread, mainstream or otherwise, which makes that claim then I think it has to be said that the claim is "against the mainstream". Until we find mainstream sites making such a claim (or other mainstream sources such as textbooks) this thread is exactly where it belongs.

Daniel


Posts: 991

Reply: 64



PostPosted: June 17, 2005 1:51 PM 

Martin,
The website I'm referring to is:
[link]

The relevant section on that page is under the FAQ: Was Mars always this cold?

I'm going to quote below, and discuss the implications in the next post.


The most likely mechanism for a warmer, wetter Mars in the past is if Mars had a larger greenhouse effect. The greenhouse effect arises as follows: visible sunlight passes through the atmosphere and is absorbed directly on the planet's surface which then radiates the energy in the (invisible) infrared; atmospheric greenhouse gases absorb some of this upwelling radiation which warms the atmosphere; the atmosphere radiates because of its finite temperature and some of this radiation is absorbed on the surface. The overall effect is to raise the surface temperature above that which would result in the absence of an atmosphere because the surface receives radiation not just from the Sun but from the atmosphere also.


For the inner planets of the solar system, Mercury, Venus, Earth and Mars, the greenhouse effect increases their average surface temperatures by 0, 500, 35 and 7 deg C respectively. Mercury has no appreciable atmosphere, Venus has an exceedingly dense atmosphere (90 bar surface pressure) of carbon dioxide (CO2), and Earth has a moderately dense atmosphere (1 bar surface pressure) which includes greenhouse gases such as water vapor (H2O) and carbon dioxide (CO2). Today, Mars has only a very thin CO2 atmosphere (0.006 bar surface pressure) and so has a modest greenhouse effect.

Daniel


Posts: 991

Reply: 65



PostPosted: June 17, 2005 1:57 PM 

The implication is that our discussion on this topic is missing some basic understanding of what the Greenhouse Effect really is. I admit, I didn't fully understand until the FAQs (excellent) explanation.

We all realized that greenhouse gasses absorb heat - but we never really discussed the fact that it needs all the other gasses (higher atmospheric density) to help transmit that thermal energy back to the surface (well maybe TR did - but he didn't explain it very well). We touched upon it with the day/night arguments, but I don't think either of us fully understood the implications...

So Mars might have the chemicals in the atmosphere to trap heat, but it is not dense enough to transmit that heat back effectively to the surface. It has one half of the equation - but not the other half, which Earth and Venus have in more abundance.

Martin Gradwell


Posts: 323

Reply: 66



PostPosted: June 17, 2005 2:00 PM 

Re: reply 62. TR says "I think that point is that, even if Mars has 25 times the amount of carbon dioxide than earth, that this CO2 is less dense."

But it *isn't* less dense. That's my point. The atmosphere as a whole is less dense, but the CO2 component isn't. If we use Hynee's figures, above, then on Earth CO2 is 365 parts per million. I think that you are under the misapprehension that CO2 on Mars is maybe 25 times denser in terms of parts per million. but 25 times 365 would be 9125 parts per million, i.e. just under one percent. CO2 on Mars is not just under one percent of the Martian atmosphere. It is 95 percent of the Martian atmosphere. 950000ppm.

The density of CO2 on Mars is 25 or more times the density of CO2 on Earth in absolute terms. Not just as a percentage of the total atmosphere. There is more atmospheric CO2 on Mars than there is on Earth, period. It weighs more. If you counted up the atoms you'd be counting for a lot longer on Mars. By any measure you can think of, there's more on Mars. That is why I reckon that there should be a huge greenhouse effect on Mars, and as far as I can tell the figures bear me out. There *is* a huge greenhouse effect on Mars, far larger than the effect on Earth, and a million sites saying that there's no greenhouse effect there wouldn't make the slightest difference to the figures.

Daniel


Posts: 991

Reply: 67



PostPosted: June 17, 2005 2:11 PM 

Hi Martin,
If you haven't already, take a look at the posts I made above. What you are saying is absolutely right and absolutely wrong. The Martian atmosphere may "catch" a lot more heat coming back up from the surface as a result of the higher CO2 density compared to Earth.

But global warming is more than catching heat - the atmosphere needs to transmit it back to the surface - otherwise its just going to radiate out into space anyway. From a climate perspective - its only really Global Warming if the surface is warming up - the upper atmopshere doesn't count.

So the problem with the Martian atmosphere, is that it isn't thick enough to retain the heat for very long, or radiate/convect/transmit the heat back to the surface. Since it can't get the heat back down to the surface, it can't complete the Greenhouse cycle.

Daniel


Posts: 991

Reply: 68



PostPosted: June 17, 2005 2:24 PM 

Not meaning to keep posting over and over - but I realize that my last post STILL isn't explicit enough. I'm going to try again - with the operative terms in caps.

Martin - you are probably right when you say that Mars's atmosphere absorbs more heat RADIATION from the surface than Earth's does.

But for global warming to occur - the atmosphere needs to get that back to the surface. And atmosphere's do that via CONDUCTION - which is more efficient as density increases. So as a result, even though more RADIATION is trapped, the low density means that only a very small amount reaches the surface thanks to CONDUCTION.

They're Rocks


Posts: no

Reply: 69



PostPosted: June 17, 2005 2:35 PM 

Just a couple of quick points, as I haven't time for a long post.

I really hope RedSky returns to this discussion, because he is a meteorologist. I'm certainly not.

Martin, as you know, CO2 is not the only thing contributing to a greenhouse effect. If it were, then clearly the earth would be a very, very cold place. Now I hold that the presence of trace CO2 on earth, in conjunction with a lot of water vapor (also contributing to greenhouse) in the context of a thick, damp atmosphere is what traps heat and makes earth warm. On Mars, let's stipulate that there is more CO2 in an absolute sense than there is on earth; and further, that these CO2 molecules are closer to one another than they are on earth, if only because the earth has such a small amount of C02. Even given these facts, the overall thinness of Mars' atmosphere is not enough to create the kind of greenhouse effect we find on earth, because on earth you've got to take into account not just CO2 but also water vapor and albedo and closeness to the sun and a number of other factors. There clearly [i]is[/i] a greenhouse effect on Mars, but it is slight compared to that of earth.

Extra Sense


Posts: 1471

Reply: 70



PostPosted: June 17, 2005 3:30 PM 

You rockhead lawyers, crack me up with your greenhouse effect interest.

Better talk about girls, would you?

e Laughing s

Daniel


Posts: 991

Reply: 71



PostPosted: June 17, 2005 3:33 PM 

No matter how stupid your intensions ES, we'll always find a way to get something useful out of your topics, despite your participation.

By the way - we grown-ups discuss WOMEN.

Gingle Blingle Stoogleplex Frok Lorif Joiem Korknle


Posts: no

Reply: 72



PostPosted: June 17, 2005 4:24 PM 

And women discuss nothing but THEMSELVES. Fascinating, captain.

They're Rocks


Posts: no

Reply: 73



PostPosted: June 17, 2005 4:31 PM 

It always cracks me up when I see Gingle's name. Laughing

Martin Gradwell


Posts: 323

Reply: 74



PostPosted: June 17, 2005 5:34 PM 

Re: reply 67.The most comprehensive description of the Earth's global warming and energy budget that I've been able to find is

[link]

This states that.

"The infrared radiation energy absorbed by the greenhouse gases heats the atmosphere. The energy is shared by all gas molecules by conduction, i.e., collisions between the greenhouse gases and non-greenhouse gases."

The fact that this process of sharing energy by collision is mentioned here seems to indicate that it is significant, but in the energy budget I can't see where the energy transferred to non-greenhouse molecules ultimately goes. If it's just transferred back and forth between greenhouse and non-greenhouse molecules then it's not significant because there's no net energy flow. On the other hand if it's ultimately transmitted to the ground via conduction then that's significant, but it isn't what the diagram shows. 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. It's all very complicated.

Every other site I've seen, if it attempts to explain the greenhouse effect at all, just says more or less that it is caused by the greenhouse gases in the atmosphere. and the other gases play no noticeable role. The process can be summarized as

1) visible light from the sun passes through the atmosphere and is absorbed by the ground.
2) Infrared photons are emitted by the ground. They do not interact with non-greenhouse molecules but are (with a few exceptions) absorbed by greenhouse gas molecules in the atmosphere.
3) The greenhouse gas molecule will eventually re-radiate, producing a new infrared photon which can go in any direction - up, down or sideways.
4) If the photon goes downward then it is likely to reach ground level, contributing to warming there. On the other hand if it goes upwards or sideways then it is likely to be absorbed by another greenhouse gas molecule, and we can repeat from step 3, until eventually a photon is either absorbed by the ground or lost to space.

If all the sites describing this process in these simple terms are wrong, and the non-greenhouse gases do play a significant role, then Mars could be warmed by adding *any* gas to the atmosphere. It doesn't matter what. We don't need greenhouse gases there because the atmosphere there already has plenty. All it needs is bulk.

But in that case, what is wrong with my simple calculation in reply 23 which seems to indicate that there *is* a greenhouse effect on Mars already, making it "a whole 83 degrees Celsius warmer than you'd expect if Mars had just the same amount of greenhouse effect as Earth has"?

Re: reply 69. "CO2 is not the only thing contributing to a greenhouse effect" - true, and it probably isn't the most significant contributing factor either. Water vapour probably occupies that spot. But if there was 26 times as much CO2 in the Earth's atmosphere as is currently the case, i.e. if the density of CO2 on Earth was the same as on Mars, then CO2 would be the most important factor, by far.

"on earth you've got to take into account not just CO2 but also water vapor and albedo and closeness to the sun and a number of other factors."

- yes, all these things will have some influence on surface temperature. But all these factors apart from the water vapour are distinct from the greenhouse effect and have no bearing on whether a greenhouse effect is present or not.

Extra Sense


Posts: 1471

Reply: 75



PostPosted: June 17, 2005 10:40 PM 

Martin,

I think you are right qualitatively, but to arrive with precise credible numbers one has to cteate a math model of the atmosphere and for the heating-cooling cycle of it, that would show greenhouse effect upon the temps.

Should not be too hard to get it done, but this goes beyond just talking about things, like we do here. Your estimate is the best available, so it must be used until such time.

es

Hynee


Posts: 200

Reply: 76



PostPosted: June 18, 2005 10:46 AM 

Re reply 74, basically what your deduction shows is that eventually all the IR photons will escape to space, which backs up some other thinking of mine, that the greenhouse gases will heat up in the same way that 'naked' ground will, and radiate their heat away in exactly the same way, through black body radiation.

We need a good explanation of how greenhouse gases trap heat in an atmosphere.

They're Rocks


Posts: no

Reply: 77



PostPosted: June 18, 2005 11:31 AM 

The plain fact is, Mars has a greenhouse effect, but it is negligible. This is essentially true by definition -- it has extremes of warm and cold that would not exist in a robust greenhouse environment. At night, temperatures drop to an extreme cold in a way that they would not if the greenhouse effect were robust. By inference to the best explanatin, the reason for the low greenhouse effect, even in the presence of abundant C02, is the thinness of the atmosphere. This hypothesis stands unrefuted.

Martin Gradwell


Posts: 323

Reply: 78



PostPosted: June 18, 2005 3:57 PM 

Re: reply 75. ES, you're right that we need a model. Does anyone reading this know of a reasonably simple but more-or-less accurate freely downloadable climate model which incorporates the greenhouse effect? Something written in an open-source statistical modelling language such as R would be ideal.

Re: reply 76. Hynee writes, "what your deduction shows is that eventually all the IR photons will escape to space .. the greenhouse gases will heat up in the same way that 'naked' ground will, and radiate their heat away in exactly the same way, through black body radiation"

Yes. Energy is not trapped in the sense that it enters the atmosphere and doesn't get away again. All the energy that enters the Martian atmosphere must get away eventually. If that wasn't the case then each day Mars would be warmer than the previous day - we really would have a "runaway greenhouse effect" which presumably wouldn't stop until Mars was as hot as the sun - but the real greenhouse effect isn't anything like that.

Re: reply 77. TR says "it (Mars) has extremes of warm and cold that would not exist in a robust greenhouse environment"

But, why should the Greenhouse effect reduce the daily temperature range? It increases the minimum temperature, which will normally occur in the night, but it also increases the maximum temperature, and probably by a greater degree. This is because the greenhouse effect is in operation both day and night, but it is greater during the day, when the ground is hotter and therefore radiating more IR. Unless you can see some flaw in my logic here.

It's convection which keeps the daytime temperature close to the nighttime temperature on Venus. *Not* the greenhouse effect. It's convection plus the existence of substantial bodies of liquid water (seas and oceans) which lessens the diurnal temperature variation on Earth - so you get a lot more temperature variation at the centres of continents than you do at the coast. Do you think there's a bigger greenhouse effect at the centres of continents?

I haven't seen a webpage outside of this thread yet which claims that the greenhouse effect lessens the extremes of warm and cold. On the contrary, the big worry everywhere except in the White House seems to be that an increasing greenhouse effec will lead to *greater* extremes of warm and cold. Do you have a reference to a site which backs up the claim that the sort of temperature variations we see on Mars "would not exist in a robust greenhouse environment"?

Martin Gradwell


Posts: 323

Reply: 79



PostPosted: June 19, 2005 5:39 AM 

Re: reply 68. Daniel, it sounds plausible, that you need greenhouse gases to absorb IR radiation from the ground, but you need a dense atmosphere to conduct the heat back down. But I'm willing to bet that you can't find a site which actually says so. Sites which say that there's no greenhouse effect on Mars because the atmosphere there is too thin don't count, because that's just handwaving.

What you will find is lots of sites which say you could warm Mars by adding a small quantity of a powerful greenhouse gas such as octofluoropropane into the atmosphere there. Which, if true, implies that the bulk of the atmosphere really isn't important, what really matters is the quantity and power of the greenhouse gases it contains.

What you won't find is sites suggesting, like I did in reply 74, that Mars could be warmed by adding *any* gas to the atmosphere because it already has plenty of greenhouse gases and just needs bulking up.

And what you won't find any more in google is any link to this discussion.

A couple of days ago, as I said in reply 63, Googling 'Mars "greenhouse effect"' got you this discussion, on the first page of results, in position number 4. By yesterday we had moved up to the number 3 slot. Today, nothing. Nada. Nil. Zilch. Zip. Rien. Admittedly I only searched the first eight pages, but googling 'site:markcarey.com Mars "greenhouse effect"' will confirm that as far as google is concerned this thread doesn't exist any more. You're a figment of my imagination, and I'm a figment of yours.

It's as if someone has had a quiet word with google. "Hey, you can't have a thread in an "against the mainstream" forum which suggests that "approximately 55,600" mainstream sites are spouting rubbish, and put that thread above all but two of those mainstream sites. You can't have a link to a thread like that *at all*."

Extra Sense


Posts: 1471

Reply: 80



PostPosted: June 19, 2005 6:20 AM 

Martin,
re:94

Which brings us back to that Mainstream science is brain dead thread and to that collusion between that pseudoscience and the brain dead "mainstream media", which google is trying to imitate.

e Cool s

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