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Post by hunter on Dec 16, 2009 4:53:25 GMT
Sorry. My flippancy was really because the point I was making is not really controversial and doesn't relate to the greenhouse effect per se. I think the Mars argument is as follows. 1. While there is 10 times as much CO2 in Mars' atmosphere as in earth, there is no water vapour. 2. Current earth's total greenhouse effect is about 33C 3. If earth got 10 times as much CO2 its temperature would rise a further 9C or so - to 42C. 4. If water vapour is 2/3 of the greenhouse effect, this suggests that without water vapour, the greenhouse effect would be 14C on earth. 5. This suggests that the greenhouse effect on Mars might raise its temperature 14C above the Stephan-Boltzmann expected value. Mars has a large diurnal cycle, and big temperature gradient from equator to the pole because of the thinner atmosphere and the fact that there is so much CO2 (which therefore radiates a bigger proportion of the total energy in its atmosphere). Dust in Mars' atmosphere has a big effect on Mars' weather. On earth, water vapour is very important. The differences in the atmosphere might make the expected greenhouse effect more than 14C or less than 14C. I suspect it is less than 14C because the planet cools so quickly. However it is not clear to me whether our knowledge of the surface temperature of the planet is known in sufficient detail to detect a variation from the Stephan-Boltzman basic calculation of even as much as 14C. The so-called greenhouse effect may raise Earth temps some, but the average temp on Earth is The average temp of earth is 13oC wiki.answers.com/Q/What_is_the_average_temperature_of_Earth%27s_surface
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Post by Purinoli on Dec 16, 2009 10:53:21 GMT
Sorry. My flippancy was really because the point I was making is not really controversial and doesn't relate to the greenhouse effect per se. I think the Mars argument is as follows. 1. While there is 10 times as much CO2 in Mars' atmosphere as in earth, there is no water vapour. 2. Current earth's total greenhouse effect is about 33C 3. If earth got 10 times as much CO2 its temperature would rise a further 9C or so - to 42C. 4. If water vapour is 2/3 of the greenhouse effect, this suggests that without water vapour, the greenhouse effect would be 14C on earth. 5. This suggests that the greenhouse effect on Mars might raise its temperature 14C above the Stephan-Boltzmann expected value. Mars has a large diurnal cycle, and big temperature gradient from equator to the pole because of the thinner atmosphere and the fact that there is so much CO2 (which therefore radiates a bigger proportion of the total energy in its atmosphere). Dust in Mars' atmosphere has a big effect on Mars' weather. On earth, water vapour is very important. The differences in the atmosphere might make the expected greenhouse effect more than 14C or less than 14C. I suspect it is less than 14C because the planet cools so quickly. However it is not clear to me whether our knowledge of the surface temperature of the planet is known in sufficient detail to detect a variation from the Stephan-Boltzman basic calculation of even as much as 14C. In the past our Earth has gone through a "snow/ice ball" phase. Simply because there was dry air. Due to tectonic movements and consequently volcanic activities oceans melted, glaciers retreated...and we got than photosynthesis =>life as we know it now. If there was no water vapours in the atmosfere, we would not be here. It's mainly water. CO2 levels were already about 7,000 ppm in the history of planet. Without "burning hell" on surface. What is important is that CO2 level don't fall under 140 ppm. At this point photosynthesis stopped. Secure level of CO2 is around 1,000 ppm. For global warming/cooling cloudiness, solar irradiance, cosmic rays, precession and tilt of orbit are most important. And of course, solar (in)activity and volcanoes as well. BTW, Stefan-Boltzman law is a night mare for people like you, making CO2 as prime "guilty" for greenhouse effect. Stefan was Slovenian ( Austro-Hungarian Empire at time of his life) and on our University we students had to know his laws very good. So minimizing effect of H2O on only 1/3 is blasfemy. There is 100 times more H2O in the atmosfere than CO2!! Just look at the some very usual weather ( not clime) pattern. When it is cold in the winter and no clouds you can see temps like -10 or -20 oC. Just some clouds are starting forming ( without winds !) and temps rise up for 10 oC. It's just water vapor and clouds blanket, nothing else.
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Post by steve on Dec 16, 2009 12:05:27 GMT
If you think volcanic activity could shift snowball earth just by itself, I suggest you visit Iceland.
Are you aware that the solar output was about 5-10% weaker during the last "snowball earth" period.
The "Stefan-Boltzmann" argument is about the contribution of the greenhouse effect. It doesn't say anything about the cause of the greenhouse effect (ie. water vapour, or CO2, or a large layer of Pilkington K).
What is the ration of water vapour to CO2 at a height of 5km above the surface?
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Post by steve on Dec 16, 2009 12:14:18 GMT
re: Mars The proportion of CO2 in the atmosphere of Mars (@95%) is 2,500 times greater than the proportion of CO2 in the atmosphere of Earth (@.038 %). The atmosphere of Mars is less dense than that of Earth by a factor of 100. The energy/radiation per square metre is approximately 1/2 that of Earth. The question which arises is why is the atmospheric temperature of Mars not greater than Earth's by a factor of 1.2? Conversely, why is the atmospheric temperature of Mars so much lower than Earth's. I believe Hansen inconclusively mentioned this issue a while back, although not with reference to the foregoing parameters. With half the energy (assuming albedo has been taken into account), the Boltzmann formula gives a reduction of temperature from 254K for the earth to 213K for Mars. Temperature in Kelvin = 1/( fourth root of ( energy in W/m^2)/5.67e-8) A calculation based on earth's atmosphere indicates that each doubling of CO2 raises temperatures about 1C before feedbacks relating to clouds and water vapour. If as you say, Mars has 25 times as much CO2, that is equivalent to just under 5 doublings of CO2. Since Mars has no clouds and water vapour, then assuming the same calculation applies to Mars (and I don't think it would), one might expect that the extra greenhouse effect on Mars to equate to under 5C.
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Post by donmartin on Dec 16, 2009 22:26:14 GMT
I am out of my depth, but would it not be the case that given the absolute CO2 atmospheric composition of Mars being 25 times greater than that of Earth, by applying the Stefan-Boltzman constant one would obtain a much higher atmospheric temperature for Mars than Earth. Given the relatively and proportionately greater number of CO2 molecules in the Martian atmosphere, would not the entropic state be equivalently greater producing thereby a relatively higher thermodynamic temperature at the surface of Mars. Once again, that is if you believe in little thingies bumping into each other, getting excited, and generally making things warmer.
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Post by nautonnier on Dec 16, 2009 23:59:00 GMT
The major issue here is that CO2 concentration in the atmosphere was actually measured accurately from ~1800 and in 1850 its atmospheric concentration was above today's level.
The figures being bandied about by CRU and IPCC etc are from ice core proxies which like tree rings have never been validated. Even if they _were_ relatively accurate the atmospheric concentration of CO2 at the poles is very low compared to the rest of the globe. There is even a report that the date of the cores was arbitrarily shifted 80 years or so to try to match with a measured level. But this can't be true as we know that CRU and the IPCC would _never_ contemplate altering or hiding inaccurate proxies don't we......
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Post by sigurdur on Dec 17, 2009 0:21:36 GMT
The major issue here is that CO 2 concentration in the atmosphere was actually measured accurately from ~1800 and in 1850 its atmospheric concentration was above today's level. The figures being bandied about by CRU and IPCC etc are from ice core proxies which like tree rings have never been validated. Even if they _were_ relatively accurate the atmospheric concentration of CO 2 at the poles is very low compared to the rest of the globe. There is even a report that the date of the cores was arbitrarily shifted 80 years or so to try to match with a measured level. But this can't be true as we know that CRU and the IPCC would _never_ contemplate altering or hiding inaccurate proxies don't we...... Actually, do an alalysis of the scatter plot involved in Dr. Keelings work, one can see very poor statisitical use. The levels of co2 measured between 1800-1900 were done with instrumentation that was accurate within 3%. The levels of co2 during the early 1800's were over 400ppm. The levels of the early 2000's are about on par with the levels seen in the early 1800's. Two papers published this summer have brought this into agreement as they both still stand last I heard.
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Post by sigurdur on Dec 17, 2009 0:23:54 GMT
Mars is actually an excellent planet to test AGW hypothosis. The co2 verses h2o are what the AGW hypothosis is based upon. The actual retention of heat on Mars is virtually none. So co2, in and by itself, is a very poor greenhouse gas.
H2o is a very good greenhouse gas.
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Post by brian0707 on Dec 17, 2009 3:41:08 GMT
Not being familiar with Messrs. Stephan or Boltzmann I am in over my head here. But it seems to me, the greenhouse effect reflects interraction of incoming solar radiation with ALL fluids surrounding the planet. In terms of mass, the atmosphere is a small fraction of the liquid water covering close to 80% of the planet's surface area. And oceans on any given day are absorbing (and retaining) vast amounts of incoming IR; and slowly releasing that energy in darkness.
Anybody who compares the daytime - nighttime termperature difference of inland deserts versus seaside areas clearly sees the huge influence of liquid water in the greenhouse effect.
But the foregoing discussion seems to focus solely on atmospheric heat transfer.
Is the effect of liquid water some kind of constant in the greenhouse balance? If so, it should be a pretty large one, IMO.
Just asking. Would appreciate an explanation at least approaching laymen's terms.
Cheers.
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Post by poitsplace on Dec 17, 2009 5:39:57 GMT
Anybody who compares the daytime - nighttime termperature difference of inland deserts versus seaside areas clearly sees the huge influence of liquid water in the greenhouse effect. But the foregoing discussion seems to focus solely on atmospheric heat transfer. Is the effect of liquid water some kind of constant in the greenhouse balance? If so, it should be a pretty large one, IMO. Just asking. Would appreciate an explanation at least approaching laymen's terms. Actually it's not so much the liquid water as it is the phase changes of water. Every day 1300 cubic kilometers of water evaporates and then falls as rain (when it cools). This takes 30% of the earth's entire energy budget. Vegetation and moist soil allow similar interactions inland. The other side of this water vapor interaction is that it keeps daytime temperatures lower. Deserts simply lack this buffer. An interesting side note...the water vapor over deserts and the water vapor over oceans absorbs IR radiated from the surface to essentially the same levels. There is so much water vapor in the atmosphere that there's essentially no "enhancement" of the greenhouse effect from additional vapor. The temperature of emission from the part of the spectrum impacted by water vapor is determined by the temperature...it has to be cold enough that concentration drops sufficiently to allow the radiation to pass into space. This happens just a little below 0C. so...the "positive feedback" from water vapor is a load of crap....although increased temperatures DO cause disproportionate warming of the higher latitudes as the energy pours out from the equators via various climate systems. This is technically a NEGATIVE feedback though because the disproportionate warming of other regions causes even more disproportionate radiated energy from the areas that have warmed (emissions of IR go up exponentially with temperature)
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Post by sentient on Dec 17, 2009 5:40:07 GMT
Although the subject has drifted off into the climate weeds once again (CO2 vs. H2O and not Hansen), I suggest that the entire discussion may be completely irrelevant.
Ignore Stephan-Boltzman? Why not? We can argue the efficacy of CO2 and H2O as climate drivers til the proverbial cows come home, but this is easily shown to be completely and totally irrelevant to real climate.
Did CO2 drive the ice age terminations? All the proxy data show that CO2 and global temperatures are strongly and definitely tied. The abrupt ice-age terminations that result in about a 20C change in temperature are absolutely tied to CO2. That is the truth, and there is no debate about it anymore. It is a fact. The abrupt termination warmings occur in startlingly little time, just years to a few centuries. CO2 follows between 800-1,300 years later. Same pattern with the Dansgaard-Oeschger events which populate the glacials. The rises are faster but not as strong, taking us between 1/3 to 1/2 of the difference between the two dominant states of glacial cold and interglacial warmth.
AND WE HAVE NO IDEA WHAT CAUSES THE ABRUPT WARMINGS, TERMINATIONS OR D-O OSCILLATIONS.
It remains THE greatest mystery in all of climate science.
Back to those pesky weeds for a moment, CO2 and H2O. Somehow, one is left to integrate all of the theory incumbent on Stephan-Boltzman and the anthropogenic signal due to CO2, and the hard cold facts of astonishing larger natural climate noise which we know CO2 does not cause.
Can we see the forest for the trees? If the natural noise is so dramatically larger than any estimated or predicted anthropogenic climate signal, what sort of algorEithm has anyone seen that can accurately tease such a signal out of such overwhelmingly larger background noise?
Think of it this way. I remember quite well as a child, on family camping trips to Myrtle Beach, my father setting up our small TV in the trailer and trying to tune in a channel. The screen was covered in static (noise), but one could kind of discern an anthropogenic signal coming from a faraway station, because the noise patterns would shift in such ways as to prove there was some signal buried in the noisy morass. However none of our Mark I eyeballs could tell if it was "I Love Lucy" or "Star Trek". The signal was just too weak compared to the noise.
IPCC AR4 worst case scenario yields 0.59 meters of sea level rise by 2100. The difference between the glacial and interglacial states is about 130 meters. 1/3rd would be 43.3 meters, 1/2 65 meters if the D-O oscillations provided enough time for sea levels to respond. During the last interglacial back, the Eemian, or MIS-5e sea levels topped out at 20 meters higher than present. During MIS-11, four interglacials back, 21.3 meters higher than present. And MIS-11 was at an eccentricity minimum, just like we are today.
Starting to get the picture?
For the sake of discussion, let's propose that what we observed in the proxy data is really backwards, and CO2 is the driver of the abrupt warmings. Let's say we enact whatever emergency legislation we need to reduce it to any level you suggest, and fast, so we can avert this IPCC worst case scenario. As we pat ourselves on our collective backs, sea level shoots up 20 meters anyway, like it has at least twice before in the past 400,000 years.
Feeling better yet?
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Post by Purinoli on Dec 17, 2009 8:53:21 GMT
Steve said:
If you think volcanic activity could shift snowball earth just by itself, I suggest you visit Iceland.
Are you aware that the solar output was about 5-10% weaker during the last "snowball earth" period.
TheStefan-Boltzmann argument is about the contribution of the greenhouse effect. It doesn't say anything about the cause of the greenhouse effect (ie. water vapour, or CO2, or a large layer of Pilkington K).
What is the ration of water vapour to CO2 at a height of 5km above the surface?[/quote][/i]
Less Sun's output at that time certanly can't be the cause of Iceball Earth because before that period Earth was not covered completely with ice ( and Sun's output was even lower). The cause was probably change in Earth orbit and tilt of axis as a trigger. At the time of iceball E. CO2 accumulated in the atmosfere to the amount of 13% (from volcanoes). And also CH4 accumulated faster than decomposed. This probably cause warming again and retreat of glaciers from equatorial regions. Once there were oceans again, CO2 could sink into water and equilibrium on higher global temps was established. water vapour started ruling as CO2 levels felt on sub 10.000 ppm...
About Stefan-Boltzmann law I just claim that in case of CO2 its influence is overestimated and simply don't comply with the law.
Ratio of water/CO2 at 5 km has less influence simply because of absolute lower levels compared to amounts at lower heights. But of course should still have influence.
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Post by steve on Dec 17, 2009 9:54:25 GMT
Not being familiar with Messrs. Stephan or Boltzmann I am in over my head here. But it seems to me, the greenhouse effect reflects interraction of incoming solar radiation with ALL fluids surrounding the planet. In terms of mass, the atmosphere is a small fraction of the liquid water covering close to 80% of the planet's surface area. And oceans on any given day are absorbing (and retaining) vast amounts of incoming IR; and slowly releasing that energy in darkness. Anybody who compares the daytime - nighttime termperature difference of inland deserts versus seaside areas clearly sees the huge influence of liquid water in the greenhouse effect. But the foregoing discussion seems to focus solely on atmospheric heat transfer. Is the effect of liquid water some kind of constant in the greenhouse balance? If so, it should be a pretty large one, IMO. Just asking. Would appreciate an explanation at least approaching laymen's terms. Cheers. Lets be clear that a basic application of Stefan-Boltzmann is a first look at the problem and misses out vast amounts of details. The Stefan-Boltzmann equation is simply an equation that tells you how much energy a body radiates according to its temperature. We also know approximately how much energy the earth and Mars receives and absorbs from the Sun. Balancing the two gives a first order idea of what the temperature should be. Because planets are warmer near the equator during the day, and colder at night or near the poles, the amount of radiation emitted by different parts is not the same. So a second order approach requires that you integrate over the surface of a sphere. As the earth has a relatively even temperature whereas Mars (because of its thin atmosphere) has a much more variable temperature. The first order approximation is not too bad for the earth but worse for Mars. (The earth has a more even temperature than you'd think because the relevant temperature is the temperature of the layers of atmosphere above most of the greenhouse gases - ie. above the water vapour. This layer is higher at the equator than at the poles because of the stronger convection and more moist air, so some of the difference in surface temperature is cancelled out).
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Post by steve on Dec 17, 2009 10:08:33 GMT
Steve said: If you think volcanic activity could shift snowball earth just by itself, I suggest you visit Iceland.
Are you aware that the solar output was about 5-10% weaker during the last "snowball earth" period.
TheStefan-Boltzmann argument is about the contribution of the greenhouse effect. It doesn't say anything about the cause of the greenhouse effect (ie. water vapour, or CO2, or a large layer of Pilkington K).What is the ration of water vapour to CO2 at a height of 5km above the surface?[/i] Less Sun's output at that time certanly can't be the cause of Iceball Earth because before that period Earth was not covered completely with ice ( and Sun's output was even lower). The cause was probably change in Earth orbit and tilt of axis as a trigger. [/quote] I didn't say it was the cause. You suggested that the high levels of CO2 would have prevented snowball earth if the CO2 theories were right. I said that you had to look at both CO2 levels *and* the solar output at the time. Both gases have influence. The point is a lot of the radiation emitted near the surface is reabsorbed. Adding more greenhouse gases near the surface doesn't make much difference. Hence some sceptics crude suggestion that spitting on the ground won't make a bit of difference. When you get up to 5km or so, the atmosphere is thinner and there is less water vapour, so a proportion of the radiation emitted goes into space (so cooling the earth). Increasing the levels of greenhouse gas *here* therefore has an impact. The impact is to raise the height in the atmosphere from which radiation escapes to space by a bit. Because the height is raised, the emissions are coming from a colder location. Because the emissions are coming from a colder location, Stefan-Boltzmann tells us that the emissions will be less. Because the emissions are less, the earth is out of radiation balance and may tend to absorb more than it emits until the atmosphere readjusts due to the effects of the radiation imbalance. More first order approximations: based on a lapse rate of about 6C per 1000 metres, raising CO2 from 280-560 ppm would need to raise this effective emitting layer by about 150 metres - not a great deal given that at 5km or so the relative importance of CO2 is quite high due to the lack of water vapour.
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Post by northsphinx on Dec 17, 2009 21:23:45 GMT
Stefan-Boltzmann law is applicable for black body radiation. The earth is not a black body. Far from it. And: Transmittance of IR radiation in the atmospheres well known. As here en.wikipedia.org/wiki/File:Atmosfaerisk_spredning.gifen.wikipedia.org/wiki/TransmittanceThe atmosphere is opaque in certain spectra. But what some people like to forget a few important things. The CO2 spectra band is already 100% opaque in well know and narrow bands, as the tranmittanse picture show. These band will not get wider with more CO2 in the atmosphere. Water as vapor have a much larger bandwith and a stronger variation in the atmosphere. But most important is that cloud cover the whole IR spectrum. It is just a issue of cloud thickness and coverage. Result? You can add as much CO2 as You want that will not make any changes. It is all about how much cloud there is in the atmosphere that matters. The earth is acting as a selective surface with a absorption of about 0.7 and with a lower emissivity. en.wikipedia.org/wiki/Selective_surfaceFor thermal balance of earth is the emissivity about 0.6. (I sell solar panels for living and are used to calculate radiation balances for selective surfaces as well as annual solar radiation. The earth is nothing else than a big solar collector. I benefit from government's interest in renewal energy but I don't agree on the CO2 theory.) From a local climate view is the issue also where the cloud is forming, because that drive the global wind patterns. Consider the monsoon wind patterns as an example. The climate forcing is so simple as wind directions.
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