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Post by hunterson on Nov 13, 2010 16:54:19 GMT
Mars is Mars because it has almost no atmosphere, in comparison to Earth, almost 0 H2O in the atmosphere, and is much farther from the sun. It has a lot of CO2 in %, but the entire atmosphere of Mars is a tiny fraction of Earth's Comparing Mars to Earth is not much less useless than comparing Venus to Earth. Why Mars' atmosphere is like this probably has many causes. No significant magnetosphere comes to mind. This leaves Martian atmosphere more vulnerable to solar wind leaching the atmosphere away over time. It is possible the primordial rubble and subsequent rain of comets did not favor Mars being endowed with a lot of volatiles. Perhaps, if luna was formed the way we presently think it was, the collision released a lot of volatiles that were unable to escape after the destruction?
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Post by steve on Nov 13, 2010 19:34:23 GMT
hunter
Your input here is the proof that the question was poorly posed. We got over that and had a discussion about Mars instead. We can and have discussed the impact of weather and climate changes on the economy elsewhere.
I wouldn't say so at all. The fundamental physics is the same even if there are differences due to the differering pressure, the lack of water vapour feedback, the presence of dust.
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Post by hunterson on Nov 13, 2010 21:48:36 GMT
hunter Your input here is the proof that the question was poorly posed. We got over that and had a discussion about Mars instead. We can and have discussed the impact of weather and climate changes on the economy elsewhere. I wouldn't say so at all. The fundamental physics is the same even if there are differences due to the differering pressure, the lack of water vapour feedback, the presence of dust. My answer was specific to the assertion, and I was wondering why someone needed to come up with idiot assertion about CO2 and weather on a Mars thread. I am not aware of anywhere in the universe where the physics are not exactly the same. Could you be a bit more clear about what that has to do with the differences between Mars, Earth and Venus?
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Post by af4ex on Nov 14, 2010 4:43:39 GMT
> ... come up with idiot assertion ... Dude. Chill. Inflammatory rhetoric doesn't help the discussion. The whole idea of this thread was that Mars seems to be an ideal lab to test the "CO2 Warming Hypothesis" because the atmosphere is almost pure CO2 and very little water vapor or other gases (or people) to complicate the argument. We observe very little of this so-called "Greenhouse Effect" on Mars, even though the effective concentration of CO2 on Mars is much higher than on Earth. Why is that? (rhetorical question) This is an important issue because, on Earth, CO2 GH warming is blamed for the imminent catastrophic and disastrous changes to our climate caused by man-made CO2, the so-called CAGW (Catastrophic Anthropogenic Global Warming) argument. I happen to be a CAGW skeptic and am inclined to believe that CAGW involves a lot of "hand waving" (i.e. no convincing proofs) about CO2. This weak GH effect on Mars seems to bolster the skeptics argument that CO2 warming is exaggerated. But I'm willling to hear civil arguments to the contrary on this thread. Steve and I were discussing this. He believes the weak GH effect on Mars can be blamed on the atmospheric pressure (about 1% of Earth). The Lacis paper (above) also makes this same assertion, that high pressure broadens the absorption lines and enhances the GH effect on Earth. But in order for me to accept this I need to see some quantification or experiment results to illustrate this effect. I'm not denying it, but it's just hand-waving, to me, unless I can see how big or little this effect is. BTW, Steve, I found the inelastic scattering effect on molecules, analogous to the Compton effect on electrons. It's called "Raman scattering". Don't know exactly how applicable it is to these arguments, but it accounts for the energy shift (up or down) when IR photons hit molecules, under certain conditions. en.wikipedia.org/wiki/Raman_scattering
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Post by af4ex on Nov 14, 2010 14:18:37 GMT
Notes while reading the Lacis paper: wattsupwiththat.files.wordpress.com/2010/10/lacis101015.pdfQuote (from the introductory part, emphasis mine): "Now, further consideration shows that CO2 is the one that controls climate change." This is paper's main point: CO2 is the critical 'control knob' that determines the impact of GHG's on the climate. Note that they didn't say 'new evidence' or 'new model'. The paper is just restating the old AGW positions, with new rhetoric, for Science magazine, which is known for its AGW stance. The main finding of the paper, that a recent run of the Goddard GISS modelE tool shows that CO2 controls everything, is not surprising. It's not surprising because of the way the model parameters were set up. Quote: "In round numbers, water vapor accounts for about 50% of Earth’s greenhouse effect, with clouds contributing 25%, CO2 20%, and the minor GHGs and aerosols accounting for the remaining 5%. Because CO2, O3, N2O, CH4, and chlorofluorocarbons (CFCs) do not condense and precipitate, noncondensing GHGs constitute the _key_ 25% of the radiative forcing that supports and sustains the entire terrestrial greenhouse effect, the remaining 75% coming as fast _feedback_ contributions from water vapor and clouds." So the "consideration" alluded to amounts to the initial assumption that water and clouds are not to be considered as "forcing" agents because they can 'condense', even though recognized that they constitute 50% of the GH effect. So they ran a GISS model with these input parameters (Fig 1 below) Feedback: water vapor, cloud Forcing: C02,O3,N2O,CH4,CFC So, assuming that H2O has no forcing effect, the model says CO2 rules. Surprise? Just because water can change states doesn't mean it can't have a powerful forcing effect as a vapor. So I think the entire premise of this paper is misleading. But still, it's an interesting paper especially because it talks about our "Mars Greenhouse" and the 'line broadening' issue we're discussing here. Attachments:
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Post by af4ex on Nov 14, 2010 14:47:42 GMT
af4ex wrote: > The main finding of the paper, that a recent run of the > Goddard GISS modelE tool shows that CO2 controls > everything, is not surprising. It's not surprising because > of the way the model parameters were set up. One more insight: I consider the GISS model to be an important tool in climate research. Not because it's "always right", but because it's been around for a while, well understood and freely available for anyone to play with. www.giss.nasa.gov/tools/modelE/In fact we could all download and modify the model to spit out whatever conclusions we want. That's why models are useless unless validated by observations. Models that can't predict or explain observations of nature are incorrect to the degree that they are inaccurate. [Citation for this assertion? Perhaps the Jewish Bible: Deuteronomy 18:21-22 www.mechon-mamre.org/p/pt/pt0518.htm] The crux of the AGW hypothesis is that the AGW models predict warming climate. Where is the warming? Possibly it's too early to completely reject this hypothesis. But there's a sense of urgency: the CAGW side is predicting doom and gloom. The Skeptics are complaining about their wallets getting lighter. So we need to get off our collective haunches and resolve this issue. But it's a lot like trying to call heads or tails while the coin is still in the air. :-]
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Post by steve on Nov 15, 2010 10:25:28 GMT
Of course! But models *are* validated by observations. Obviously they do not perfectly match observations, and where they *do* match observations they may not match them for the right reason.
But a lot of models are developed for weather forecasting before climate, and they do not appear to require a water vapour forcing mechanism and there is no physical mechanism that I am aware of that would result in such a forcing.
If a water vapour forcing mechanism is being proposed, what is the mechanism?
The physics assumption is that the amount of water vapour that is evaporated or that condenses is a local effect dependent on local conditions and happens in a relatively short timescale. Normally days to weeks. At most perhaps many years for the stratosphere. This means that a model could statistically get it right.
What could make water evaporation and condensation behave differently to allow it to act as its own control knob rather than as a feedback?
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Post by nautonnier on Nov 15, 2010 11:40:42 GMT
Of course! But models *are* validated by observations. Obviously they do not perfectly match observations, and where they *do* match observations they may not match them for the right reason. But a lot of models are developed for weather forecasting before climate, and they do not appear to require a water vapour forcing mechanism and there is no physical mechanism that I am aware of that would result in such a forcing. If a water vapour forcing mechanism is being proposed, what is the mechanism? The physics assumption is that the amount of water vapour that is evaporated or that condenses is a local effect dependent on local conditions and happens in a relatively short timescale. Normally days to weeks. At most perhaps many years for the stratosphere. This means that a model could statistically get it right. What could make water evaporation and condensation behave differently to allow it to act as its own control knob rather than as a feedback? "What could make water evaporation and condensation behave differently to allow it to act as its own control knob rather than as a feedback?"You are asking the incorrect question Steve Is it possible to have a world where there is NO water vapor considering that the oceans make up ~70% of the surface? Even ice will sublimate into a dry atmosphere. In a world without CO 2 (and thus without life), the water vapor from evaporation/sublimation of the surface would start convection even without heat as wet air is lighter than dry air. The dry air would replace the rising more humid air would pass over the surface and itself become humid and start rising. The sun on the tropics would be sufficient to accelerate evaporation and convection even in a colder world. Once started the hydrologic cycle runs on its own without the need for CO 2 or other 'green house' gases. The presence of CO 2 may slightly increase the hydrologic cycle but it is not the sole reason that water evaporates cf Henry's Law. The effect of water vapor convected into the atmosphere on atmospheric heat retention is all positive feedback until clouds start to form. As sufficient water vapor reaches a dewpoint as it rises and clouds form, then the feedback starts going negative due to cloud albedo and optical depth. If you want to have a control knob then you should consider water vapor and the hydrologic cycle as the thermostat which will keep the Earth at a within a stable temperature range regardless of the position of the control knob. The problem with the models - as we have discussed before - is that they run on the assumption that water only evaporates in proportion with levels of CO 2 - a totally false assumption. That leads to the equally false - water is condensing therefore it has a short lived effect - which only considers one side of the Hyrdrologic cycle - that's why its called a CYCLE. Perhaps if the models included a hydrologic cycle that did NOT assume that CO 2 was necessary for water to evaporate and also modeled clouds and latent heat correctly they would be closer to what is really happening. As it is there are -as you would say- a lot of double headed assumptions that lead to the totally incorrect results and parameterization to make the results match the observations.
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Post by steve on Nov 15, 2010 11:59:17 GMT
nautonnier
Are you quite sure you mean what you say here!?
Water in models evaporates and precipitates according to the temperature and pressure, not the CO2.
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Post by af4ex on Nov 15, 2010 12:15:01 GMT
steve: > Of course! But models *are* validated by observations. But there is a tendency to believe a model as an "oracle". We all do this. Our human sensory organs provide mostly qualitative and only crude quantitative measures of distance, time, pressure, illumination etc. All of our external quantitative measures are obtained through models. The thermometer on your back porch, for example, doesn't give you the real "temperature" there (in reality, a dynamic distribution over time and space). It uses a model, based on thermal expansion properties of materials or flow of current through a thermocouple to crank out a "point estimate" number we call "temperature". Your wristwatch and tape measure are also "models". employing models which partition time and space into equally-divided (more or less) subsets and counting them. (Sometimes you have to do some of the counting yourself). Again the numbers they produce are only approximate, because the it's impossible to make the subsets perfect. But we tend to believe in our watchs and rulers, as if they were oracles. en.wikipedia.org/wiki/Oracle_machineSo "validating a model" _always_ means comparing the output of some model, usually one we don't trust, to another model which we do trust (sometimes too much). >... models are developed for weather forecasting > before climate, and they do not appear to require a > water vapour forcing mechanism ... and may produce a correct prediction for the wrong reason, as you pointed out. > ... there is no physical mechanism that I am aware of that would > result in such a forcing. If a water vapour forcing mechanism is > being proposed, what is the mechanism? Water vapor is a GHG, with humongous absorption bands. So it absorbs radiated heat just like CO2, on a much larger scale. Yes, it changes state, which complicates the model. But let's keep that issue separate for our analysis. Actually it's pretty obvious that water is the "control knob" here, but not in the atmosphere. In the oceans. An enormous heat reservoir whose capacity is several orders of magnitude larger than the atmosphere. Again, for those who came in late, that's why our Mars Greenhouse, here in this thread, is so useful. We can study the CO2 warming hypothesis without interference from all of that ice, water and steam!
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Post by steve on Nov 15, 2010 13:03:34 GMT
Although it is the climate and weather model that normally has the shortcoming, when the satellite temperature measurements were showing no warming and the ocean heat content measurements were showing cooling, the modellers said - hang on, isn't it more likely that in this case the climate model is better than the modelling of the observations. Or models sometimes show phenomena that haven't been observed at all (stratospheric cooling). Models are not oracles, they are tools (like the observing systems) to understand the real world.
I'm not sure I like the control knob analogy.
If the ocean reaches equilibrium in a few decades then it does not act as a control knob. A water-related control knob requires changes that occur without a determinate weather/climate cause.
On geological timescales, CO2 is normally controlled by the rate it is emitted (by volcanoes) compared with the rate it is absorbed (ultimately into sedimentary rocks). It's level may control the temperature, but its level is controlled by a balance of geological phenomena.
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Post by af4ex on Nov 15, 2010 14:00:18 GMT
steve: > If the ocean reaches equilibrium in a few decades > then it does not act as a control knob. The oceans will never be "in equilibrium", with all the Atlantic/Pacific decadal patterns, ninyas and ninyos, and don't forget Milankovic (or however it's spelled)! I don't think we "need" CO2 to explain these controlling effects. The coin is still in the air, but I think it's getting close to ground and the side that says "Heads, it's the Oceans!" is facing up. But we're getting way off-topic here. Forget about water vapor and feedback. Does the weak greenhouse effect on Mars imply that the effect of CO2 on Earth's climate has been overstated? Are there any quantitative models which explain the "line broadening" effect you spoke of in terms of temperature or energy?
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Post by nautonnier on Nov 15, 2010 14:07:41 GMT
nautonnier Are you quite sure you mean what you say here!? Water in models evaporates and precipitates according to the temperature and pressure, not the CO2. It was your question Steve: "What could make water evaporation and condensation behave differently to allow it to act as its own control knob rather than as a feedback?"I just explained how in your vernacular - it is its own control knob- Water vapor in the atmosphere is NOT 'just a feedback' as I explained.
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Post by af4ex on Nov 15, 2010 14:25:22 GMT
steve: > hang on, isn't it more likely that in this case the climate model is > better than the modelling of the observations. It happens all the time that a new, "untrusted" model (digital watch) eventually replaces the old, "trusted" model (spring-wound watch). I also see the Skeptics complain that climatologists rely too much on models and not enough on "real data", as if "real" data for any historical era (including the modern era) actually existed. All of that "real" data comes from models, with the more accurate models replacing the less accurate ones. But how do we know which model of Nature to believe, if they're all just "guessing"? I agree with that 6th century BC cleric, who figured out how to tell the false prophets from the true prophets and answered that very same question: 21 “You may wonder how you can tell when a prophet's message does not come from the LORD. 22 If a prophet speaks in the name of the LORD and what he says does not come true, then it is not the LORD's message. That prophet has spoken on his own authority, and you are not to fear him. We may not all agree that God is in Nature and therefore is part of it, but the basic "algorithm" is still the same. Ok, enough philosophy and religion. Back to the topic: Mars Greenhouse!
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Post by steve on Nov 15, 2010 17:44:54 GMT
steve: > If the ocean reaches equilibrium in a few decades > then it does not act as a control knob. The oceans will never be "in equilibrium", with all the Atlantic/Pacific decadal patterns, ninyas and ninyos, and don't forget Milankovic (or however it's spelled)! I don't think we "need" CO2 to explain these controlling effects. The coin is still in the air, but I think it's getting close to ground and the side that says "Heads, it's the Oceans!" is facing up. ENSO, PDO etc. are relatively short term cycles with limited effect. Milankovitch is an external forcing, so it is not the ocean acting as a control knob. I don't think there is any more I can add. Pressure broadening is a well-documented and observed phenomenon. It's not an instrument effect or an invention of AGW. Planetary scientists have concluded that the back radiation from CO2 would be only about 12 Watts/m^2 compared with the earth climate science figure of over 300W/m^2 on earth. 12W/m^2 equates to a less than 10K warming. The back radiation from CO2 is small compared with the back radiation from dust. The minute to minute temperature variation on Mars is large compared with the theoretical greenhouse effect. I don't know what observational support exists for the 12W figure.
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