eli@bbn.com (Steve Elias) (03/16/88)
In article <3772@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >>>In article <781@lf-abe.BBN.COM> eli@BBN.COM (Steve Elias) writes: jfc>[ In response to description of the greenhouse effect, which, accelerated jfc> by fossil fuel consumption, may raise the level of the oceans enough to jfc> flood coastal cities.] my comment about nuclear power is in response to JFC's statement that nuclear power will help us avoid the "greenhouse effect". se>: : : nuclear power plants also contribute nontrivial amounts of se>: : : thermal pollution into the environment, a significant factor se>: : : in the greenhouse effect, especially if more plants are built. jfc>The quote above reveals a lack of understanding of thermodynamics, wrong. it reveals that i don't agree with your opinions on the greenhouse effect theory. there is no valid model for the greenhouse effect. either one of our statements are just opinions. if you are aware of some definitive new research, please do tell. the issue is only partially a thermodynamic one. planetary and atmospheric science issues are also key. the "greenhouse effect" is pure theory, whether it is applied to Venus or Earth. it may be a commonly accepted theory, but it is far from proven. jfc>Thermal pollution is seperate from the greenhouse effect. how do you know? seriously! jfc>It is likely jfc>that the Earth is stable to the addition of small amounts of heat. it is unlikely that your statement can be backed up. power generation generates far more than a "small" amount of waste heat, regardless of the resource used for fuel. se>: an important concept: the thermal equilibrium of the planet. se>: nuclear waste heat affects the equilibrium, too. the energy se>: contained in uranium is being released with great speed, on a se>: geologic scale. the same is true for the heat and CO2 from se>: burning fossil fuels. jfc>Nuclear or chemical power plants both produce waste heat. waste heat is not a global issue unless the energy for it originates outside the earth/atmosphere system. that's the thermo concept i'm trying to stress. the greatest thermal danger is from solar power satellites, or solar farms on earth. jfc>However, chemical plants also produce carbon dioxide which does the real jfc>harm to the heat balance by trapping IR radiation. neither JFC's nor the hypothesis i am backing is proven. "my" hypothesis actually belongs to Frank Drake of Cornell U. his calculations indicate that both solar power satellites, or a great number conventional power plants, could cause a thermal runaway or other disaster. se>: when natural gas burns, the products are CO2 and water. se>: natural gas can be produced by fermenting garbage -- reversing se>: the CO2 production process... >This is an ideal case, assuming perfect combustion (another article mentioned >nitrous oxides; there may also be CO) and an effective large scale conversion >of garbage. I think I've seen figures showing that garbage can not produce >more than a very small fraction of our energy needs; I'll check these. good enough. i'm not aware of other byproducts of natural gas burning -- chemists please comment. is there any fuel which burns more cleanly than natural gas??? >I consider myself informed. I have read about nuclear power, reactor >design, and the accidents for which details have been published. all are different subjects than the one i've been discussing. >I'm sure I could imagine some worst case scenarios for coal power which >show it to be worse. (I'd start with acid rain.) John, i'm not trying to bash nuclear or coal power -- just commenting on the "greenhouse effect" theory. (i can't wait for summer.)
jwm@stdc.jhuapl.edu (James W. Meritt) (03/17/88)
In article <22138@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In article <3772@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >>>>In article <781@lf-abe.BBN.COM> eli@BBN.COM (Steve Elias) writes: > >jfc>[ In response to description of the greenhouse effect, which, accelerated >jfc> by fossil fuel consumption, may raise the level of the oceans enough to >jfc> flood coastal cities.] > > my comment about nuclear power is in response to JFC's statement > that nuclear power will help us avoid the "greenhouse effect". > >se>: : : nuclear power plants also contribute nontrivial amounts of >se>: : : thermal pollution into the environment, a significant factor >se>: : : in the greenhouse effect, especially if more plants are built. webster's new collegiate: greenhouse effect - warming of the earth's surface and the lower layers of atmosphere that tends to increase with increasing atmospheric carbon dioxide and that is caused by conversion of solar radiation into heat in a process involving selective transmission of short wave solar radiation by the atmosphere, its absorption by the earth's surface and re-radiation as infrared which is absorbed and partially reradiated back to the surface by carbon dioxide and water vapor in the air. note: no mention of thermal pollution as a direct cause. Perhaps you mean the increase in water vapor caused by the cooling of the reactors? >jfc>The quote above reveals a lack of understanding of thermodynamics, > > wrong. it reveals that i don't agree with your opinions on > the greenhouse effect theory. > > there is no valid model for the greenhouse effect. expletive deleted! Check definition of greenhouse effect. Everything measurable. No theory. Thus, there is a model. As to its validity, the effect itself is easily measured, and thus validified. Do you mean "possible long term results"? > the issue is only partially a thermodynamic one. planetary and > atmospheric science issues are also key. If you mean "long term results", this is a definite understatement! They are more than the key, they are the issue! > the "greenhouse effect" is pure theory, whether it is applied to > Venus or Earth. it may be a commonly accepted theory, but it is > far from proven. negat: see above! >jfc>Thermal pollution is seperate from the greenhouse effect. > how do you know? seriously! You could always check the definition of "greenhouse effect" >jfc>It is likely >jfc>that the Earth is stable to the addition of small amounts of heat. > > it is unlikely that your statement can be backed up. I don't know - seems that you could model this from a conservation level. Meterologist do it all the time! > power generation generates far more than a "small" amount > of waste heat, regardless of the resource used for fuel. Not on the world-wide scheme of things.check: solar constant: the quantity of radiant solar heat received normally at the outer layer of the earth's atmosphere and having an average value of about 1.94 gram calories per square centimeter per minute. Note: the world is BIG!!! What do you think melts a few feet of snow every year? Nuclear waste heat??? >jfc>Nuclear or chemical power plants both produce waste heat. > > waste heat is not a global issue unless the energy for it originates > outside the earth/atmosphere system. that's the thermo concept > i'm trying to stress. the greatest thermal danger is from solar > power satellites, or solar farms on earth. The waste heat from solar farms on earth is not from outside the earth/ atmosphere system. If the solar farm were not there, the dirt would absort just as much heat as the farm. More, infact, because none would be converted to electricity. Of course, more would (possibly) be re-radiated because solar collectors are designed to prevent just that. Now, importing it from outside might cause problems, but it would have to be a LOT of energy! Nuclear power may be viewed as originating as "outside" the earth/ atmosphere system. From the thermodynamic viewpoint, the heat was not there before. Anywhere else either, so should say "not in" the system instead of "outside" of it. For you sci-fi readers, recognize the problems from Larry Nivel's "Known Space" stories, in particular the ones associated with the Puppeteers (sp?) home world? Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
eli@bbn.com (Steve Elias) (03/17/88)
In article <114@aplcomm.UUCP> jwm@stdc.jhuapl.edu (James W. Meritt) writes: >.. dictionary definition of the greenhouse effect .. >note: no mention of thermal pollution as a direct cause. determining causality between thermal runaway and CO2 buildup quickly turns into a chicken/egg problem. water vapor & cooling techniques aren't related to the greenhouse effect theory. se>> there is no valid model for the greenhouse effect. >expletive deleted! Check definition of greenhouse effect. Everything >measurable. No theory. Thus, there is a model. As to its validity, >the effect itself is easily measured, and thus validified. i don't think Funk & Wagnall have hung out on venus for a million years... this theory is not proven! read an astro text instead of a dictionary for a more complete look... dictionaries don't make scientific discoveries! the Earth's atmosphere cannot be modeled with current technology. thus, THERE IS NO MODEL. present one and you will make history. when i say 'model', i mean a working model that can be used to see what the atmosphere will do under any specific global conditions -- the problem is IMMENSE and unsolved. >The waste heat from solar farms on earth is not from outside the earth/ >atmosphere system. not true -- they would absorb some energy that would ordinarily be reflected back into space. >If the solar farm were not there, the dirt would >absort just as much heat as the farm. no. vegetation has different reflective properties than do solar cells. >Nuclear power may be viewed as originating as "outside" the earth/ >atmosphere system. i don't think there's an easy answer to this question...
jwm@stdc.jhuapl.edu (James W. Meritt) (03/17/88)
In article <22230@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In article <114@aplcomm.UUCP> jwm@stdc.jhuapl.edu (James W. Meritt) writes: >>.. dictionary definition of the greenhouse effect .. >>note: no mention of thermal pollution as a direct cause. : : determining causality between thermal runaway and CO2 buildup quickly : turns into a chicken/egg problem. water vapor & cooling techniques : aren't related to the greenhouse effect theory. >se>> there is no valid model for the greenhouse effect. : >>expletive deleted! Check definition of greenhouse effect. Everything >>measurable. No theory. Thus, there is a model. As to its validity, >>the effect itself is easily measured, and thus validified. : : i don't think Funk & Wagnall have hung out on venus for a : million years... this theory is not proven! read an astro : text instead of a dictionary for a more complete look... I believe you are confused as to my definition: I said that the greenhouse effect, as defined, was a confirmed, easily testable model. Now, you are debating the applicability of the valid model to conditions under which is was not generated. This action is not generally recommended as "extrapolating beyond region of fit" also known as "going off on a limb" : dictionaries don't make scientific discoveries! the Earth's : atmosphere cannot be modeled with current technology. thus, : THERE IS NO MODEL. present one and you will make history. : when i say 'model', i mean a working model that can be used : to see what the atmosphere will do under any specific global : conditions -- the problem is IMMENSE and unsolved. You are incorrect in saying that the Earth's atmosphere cannot be modeled. You might be more correct to say "cannot be modeled well", but you must then define by what you mean by "well". There are many, varying, models. You probably know of some of them: can you say "National Weather Service"? Point of fact, these are the primary uses of most of the biggest machines, and one of the best applications of parallel processing. I know of a number of models in other jobs (I was a Navy meterologist) and I am afraid that I would not make history. The problem is, as you stated IMMENSE, and generally falls apart under microclimat conditions, largely due to a lack of sufficient & appropriate data. There are, apparently, more models than you know about. Try the Goddard Space Center for a good one..... >>The waste heat from solar farms on earth is not from outside the earth/ >>atmosphere system. : not true -- they would absorb some energy that would ordinarily : be reflected back into space. : >>If the solar farm were not there, the dirt would >>absort just as much heat as the farm. : no. vegetation has different reflective properties than : do solar cells. And if you read my next line you would have seen this. Why did you leave that out of your quote? Keeping score or seeking knowledge? Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
jfc@athena.mit.edu (John F Carr) (03/18/88)
In article <22138@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In article <3772@bloom-beacon.MIT.EDU> I wrote: [ In response to description of the greenhouse effect, which, accelerated by fossil fuel consumption, may raise the level of the oceans enough to flood coastal cities.] SE : nuclear power plants also contribute nontrivial amounts of SE : thermal pollution into the environment, a significant factor SE : in the greenhouse effect, especially if more plants are built. JFC : The quote above reveals a lack of understanding of thermodynamics, > wrong. it reveals that i don't agree with your opinions on > the greenhouse effect theory. > there is no valid model for the greenhouse effect. > either one of our statements are just opinions. if you are aware > of some definitive new research, please do tell. I am not aware of any serious disagreement over the nature of the greenhouse effect, only its magnitude. The Earth must be stable to small additions of heat, since the solar constant isn't really constant. There is a theory (which is somewhat controversial) that Earth+life is self-regulating (i.e., mean temp and atmospheric composition are kept constant). Certainly there must be some reason for the relatively stable climate/atmoshpere. The addition of massive amounts of non- biological CO2 may remove any stability. Remeber that fossil fuel plants produce all the thermal pollution of nuclear PLUS carbon dioxide. [question for any scientists who have studied this: has anyone added biological factors to the computer simulations of the ice ages? Last I read, the variation of the Earth's orbit and some assumptions about the response time of rock gave close results. Maybe feedback through life would improve the fit?] > the issue is only partially a thermodynamic one. planetary and > atmospheric science issues are also key. I called it a thermodynamic issue because the claim was that nuclear plants emit waste heat, and that this heat was important to the greenhouse effect. It can be proved (using thermodynamics) that ALL heat engines produce waste heat, so there is no justification in singling out nuclear power. The magnitude of the total waste heat produced relative to the total heat content of/flow through the atmosphere is much less than the amount of added Carbon Dioxide relative to the total amount (especially while we are cutting down forests). > the "greenhouse effect" is pure theory, whether it is applied to > Venus or Earth. it may be a commonly accepted theory, but it is > far from proven. JFC : Thermal pollution is seperate from the greenhouse effect. > how do you know? seriously! JFC : It is likely JFC : that the Earth is stable to the addition of small amounts of heat. > it is unlikely that your statement can be backed up. > power generation generates far more than a "small" amount > of waste heat, regardless of the resource used for fuel. See above. SE : an important concept: the thermal equilibrium of the planet. SE : nuclear waste heat affects the equilibrium, too. the energy SE : contained in uranium is being released with great speed, on a SE : geologic scale. the same is true for the heat and CO2 from SE : burning fossil fuels. JFC : Nuclear or chemical power plants both produce waste heat. > waste heat is not a global issue unless the energy for it originates > outside the earth/atmosphere system. that's the thermo concept > i'm trying to stress. the greatest thermal danger is from solar > power satellites, or solar farms on earth. Waste heat from any of the heat engines (as opposed to hydroelectric, wind, or possibly trash [see below] power) is effectively from outside, since it would not otherwise have been released into the atmosphere on such a short timescale. JFC : However, chemical plants also produce carbon dioxide which does the real JFC : harm to the heat balance by trapping IR radiation. > neither JFC's nor the hypothesis i am backing is proven. > "my" hypothesis actually belongs to Frank Drake of Cornell U. > his calculations indicate that both solar power satellites, > or a great number conventional power plants, could cause a > thermal runaway or other disaster. I read, long ago, articles on the formation of the solar system (specific issue: outside of what bounds would the Earth form like Venus [runaway greenhouse effect] or Mars [the opposite, never enough air to heat the surface]). The conclusion from this and other sources I have seen is that beyond some limit of temperature and CO2 concentration, the greenhouse effect grows very large. My impression is that in extreme quantities either CO2 or heat can cause the effect, but that it is much harder to do with heat alone. Think of CO2 as a catalyst, very small quantities of which can produce great effects. (Thermal energy is spent heating up the earth, which would then cool on a timescale of days if it were removed. CO2 produces a permanent increase in temperature, and remains afterward [until production is slowed enough for biology to take over]). SE : when natural gas burns, the products are CO2 and water. SE : natural gas can be produced by fermenting garbage -- reversing SE : the CO2 production process... >>This is an ideal case, assuming perfect combustion (another article mentioned >>nitrous oxides; there may also be CO) and an effective large scale conversion >>of garbage. I think I've seen figures showing that garbage can not produce >>more than a very small fraction of our energy needs; I'll check these. And I have... My source is an essay titled "Can Trash Save Us" by Jerry Pournelle, from a book called "A Step Farther Out" (a collection of essays on the future of humanity and some of the technical problems and promises). It was written in 1977; relevant changes between then and now are: increase in oil prices (since we import almost the same fraction of oil now as then, this shouldn't be too important to the general conclusion) and increase in energy consumption relative to trash production (I assume this on the grounds that trash is proportional to population, but energy use grows faster.). In answer to the question: how much energy can trash give us "...1.6x10^25 ergs [per year], or 4.4x10^11 kW-hours. In other words, if we captured ALL the energy from our rubbish we could produce about 2% of the energy [which JP uses to mean all forms, not just electricity, since oil imports go to others forms also] we used in 1974. Significant, yes. Important, yes. But it won't save us from Arab oil and sinking tankers." He goes on to say, assuming an efficiency of 27%, trash could produce 2% of the electricity generated, not counting processing, drying, and plant construction (or any of the costs). About costs: [quotes _Annual Review of Energy_ for figures] "[cost] ranges from around $500 pe kW for a coal-fired plant to over $1000 for some kinds of nuclear. Assuming 27% efficiency...capital cost per kW is $1100, much higher than other kinds of plant costs, which explains why electrical utilities aren't terribly interested. For $1100 a kW they can buy a nuclear BREEDER plant, whose operating costs will be lower than the value of the fuel produced." [He notes that nuclear costs are going up, and I note that the gov't doesn't like breeder plants because they produce Pu, which can make bombs.] "...If we subtract off the costs of sanitary landfill, and a number of other expenses of disposing of that growing mound of trash that gives mayors nightmares, our electrical plants begin to make sense after all: but only if we look at cities as a total system, and city budgets aren't prepared that way. Believe me, I know: I've been Executive Assistant to the Mayor of Los Angeles." [goes on to say that is not possible to raise taxes enough to build such plants, nor to persuade relevant agency to be joined with the lowly sanitation department.] Next part asks "can sewage save us?" [I paraphrase to save space] 1 ton sewage produces 225 m^3 methane = $80.00 [in 1977]. With plant costs (and interest on same) it costs $5.50 a ton to turn sewage into methane including profits from sale. [Interest is higher now, but so is fuel cost.] When Southern Calif. Edison tried to do research to make conversion more efficient, the government stopped them. The theoretical maximum, counting animal waste, is the same as for trash: 2% (which is 10% of natural gas use [reference year also 1974, we use more energy now]). You also get fertilizer out of this process. Conclusions: The total from waste is then 4-5% of energy use, assuming perfect efficiency. It helps, but isn't the answer. His recommendations: research into more efficient crops (which could then be turned into fuel without starving that part of the world which we feed), ocean thermal energy, and fusion; and tax breaks for insulation/solar homes [which I think we now have] and companies which want to do research into conservation and/or improved energy production. John Carr "No one wants to make a terrible choice jfc@Athena.MIT.EDU On the price of being free"
eli@bbn.com (Steve Elias) (03/18/88)
In <122@aplcomm.UUCP> jwm@stdc.jhuapl.edu.UUCP (James W. Meritt) writes: >I believe you are confused as to my definition: I said that the greenhouse >effect, as defined, was a confirmed, easily testable model. i understand your definition. it's not that tough. i'm writing about the greenhouse effect: the scientific theory. one which we understand more as we research and attempt to model it. our understanding of the greenhouse effect and planetary atmospheres has a long way to go. i don't think the scientific community will get bogged down when they lean things that are not in the dictionary. i'm not interested in discussing dictionary definitions of scientific discoveries & theories. does anyone mind? >Now, you >are debating the applicability of the valid model to conditions under >which is was not generated. This action is not generally recommended as >"extrapolating beyond region of fit" also known as "going off on a limb" thanks for telling me what i was debating. you are saying that the greenhouse effect IS a valid model ?? instead of telling you what you were saying, i'm asking. this action is recommended as "discussion" also known as "civil conversation". :) >You are incorrect in saying that the Earth's atmosphere cannot be modeled. >You might be more correct to say "cannot be modeled well", but you must i said "valid model" -- meaning a model that can actually be used to predict what the atmosphere will do: on both macro scales and local ones. we're nowhere near developing a model like this -- neither our computation methods nor our sensing methods are up to the job. do you concur? i'm aware of the limitations and capabilities of weather service sensing and modeling -- mostly from the computation side. >> .. another comment i made -- perhaps mistaking jwm's point .. >And if you read my next line you would have seen this. Why did you leave >that out of your quote? Keeping score or seeking knowledge? c'mon. cut the abusenet bullshit. i keep my postings short because i find 3 pages of included text to be BORING. perhaps i did omit a crucial part of that section... tally that mistake up, if you like.
eli@bbn.com (Steve Elias) (03/18/88)
In article <3851@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes:
!! there is no valid model for the greenhouse effect.
!I am not aware of any serious disagreement over the nature of the
!greenhouse effect, only its magnitude.
the general nature of the effect is certainly agreed upon.
i bet we could even find it in the dictionary!
but detailed models of any long-term atmospheric effect
just aren't around yet. you are a planetary scientist, right?
do you admit that we don't have enough data to really be able
to predict any planetary atmosphere?
as a computer dude who has studied astronomy, i'll say that even if
we did have enough data to learn how to predict atmospheres, we
don't have .001 the processing power available to do the job.
!I called it a thermodynamic issue because the claim was that nuclear plants
!emit waste heat, and that this heat was important to the greenhouse effect.
!It can be proved (using thermodynamics) that ALL heat engines produce waste
!heat, so there is no justification in singling out nuclear power.
absolutely. i'm singling out the greenhouse effect, not nuclear power.
!! waste heat is not a global issue unless the energy for it originates
!! outside the earth/atmosphere system. that's the thermo concept
!! i'm trying to stress. the greatest thermal danger is from solar
!! power satellites, or solar farms on earth.
!
!Waste heat from any of the heat engines (as opposed to hydroelectric,
!wind, or possibly trash [see below] power) is effectively from outside,
!since it would not otherwise have been released into the atmosphere on
!such a short timescale.
exactement.
!JFC: However, chemical plants also produce carbon dioxide which does the real
!JFC: harm to the heat balance by trapping IR radiation.
thermal pollution could do real harm to the heat balance, too.
especially if someone ever puts 'solar power stations' in orbit.
!My impression is that in extreme quantities either CO2 or heat can cause
!the effect, but that it is much harder to do with heat alone. Think of
!CO2 as a catalyst, very small quantities of which can produce great effects.
you bet. enough heat could start thermal runaway, just as enough
CO2 could. i read in today's paper that the current guess about
the extinction of the dinosaurs involves 3x to 5x increase in
atmospheric CO2 levels around the time they disappeared.
!(Thermal energy is spent heating up the earth, which would then cool on
!a timescale of days if it were removed.
i think John is doing some big time speculation here.
massive amounts of thermal energy would not dissipate in a
matter of days. (i mean thermal energy produced from power plants:
if we produced 10x or 100x the power we do now.) the Earth can
only radiate energy at a specific rate -- sigma T^4, cloud cover,
CO2 levels, and other stuff determines that rate.
(John then goes on to show why trash or sewage fuel production
is not the answer to it all. i brought up trash/garbage being
used to produce natural gas as a good example of a
"thermally correct :)" power source.) jfc@athena.mit.edu (John F Carr) (03/18/88)
(I think the political flaming has settled down enough that I am directing followups to sci.misc) In article <22277@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In article <3851@bloom-beacon.MIT.EDU> I wrote: [Re: greenhouse effect] : but detailed models of any long-term atmospheric effect : just aren't around yet. you are a planetary scientist, right? : do you admit that we don't have enough data to really be able : to predict any planetary atmosphere? : as a computer dude who has studied astronomy, i'll say that even if : we did have enough data to learn how to predict atmospheres, we : don't have .001 the processing power available to do the job. It depends on what level of detail you want. I mentioned an article I read in Scientific American which discussed computer simulations of the Ice Ages. Today's computers, as far as I know, do a good (but not great) job of predicting gross effects (like the Ice Ages and approximate global temperature distributions). They do an acceptable job of calculating details. In both cases the models can probably be improved, especially as more computer power gives more accurate models. In all cases, more power will help as long as we have the observational detail to get data accurate enough (which means, there is a lot of room for improvement). The statement above is just too general. JFC: However, chemical plants also produce carbon dioxide which does the real JFC: harm to the heat balance by trapping IR radiation. : thermal pollution could do real harm to the heat balance, too. : especially if someone ever puts 'solar power stations' in orbit. JFC: My impression is that in extreme quantities either CO2 or heat can cause JFC: the effect, but that it is much harder to do with heat alone. Think of JFC: CO2 as a catalyst, very small quantities of which can produce JFC: great effects. : you bet. enough heat could start thermal runaway, just as enough : CO2 could. i read in today's paper that the current guess about : the extinction of the dinosaurs involves 3x to 5x increase in : atmospheric CO2 levels around the time they disappeared. The point is, enough heat is vastly more than we are producing now (another article said 10^-7 of the Earth's energy budget is man-made). Enough CO2 seems not to be much more than we are producing now. JFC: (Thermal energy is spent heating up the earth, which would then cool on JFC: a timescale of days if it were removed. : i think John is doing some big time speculation here. : massive amounts of thermal energy would not dissipate in a : matter of days. (i mean thermal energy produced from power plants: : if we produced 10x or 100x the power we do now.) the Earth can : only radiate energy at a specific rate -- sigma T^4, cloud cover, : CO2 levels, and other stuff determines that rate. Timescales to consider: The atmosphere heats and cools in hours (now that I think about it, I seem to remember deriving a cooling time for atmospheres in a course I took on planetary science. I'll try to find this). Looking at daily temperature curves I have estimated a time constant of no more than a day. (i.e. the atmosphere effectively follows man-made inputs with no lag). The surface is a trickier matter, as is the ocean. I would guess the time constant from the lag of seasons behind the driving force: the Earth's axial tilt. The lag is slightly less than 3 months; this would make the best-fit timescale [i.e. if one treated the earth's temp. as a driven 2nd order system] about the same. (I hear the flames coming now: what is this! someone is threatening to have a rational discussion in talk.politics.misc!) John Carr "No one wants to make a terrible choice jfc@Athena.MIT.EDU On the price of being free"
eli@bbn.com (Steve Elias) (03/18/88)
In article <3862@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >In article <22277@bbn.COM> eli@BBN.COM (Steve Elias) writes: >: but detailed models of any long-term atmospheric effect >: just aren't around yet. you are a planetary scientist, right? >: do you admit that we don't have enough data to really be able >: to predict any planetary atmosphere? > >: as a computer dude who has studied astronomy, i'll say that even if >: we did have enough data to learn how to predict atmospheres, we >: don't have .001 the processing power available to do the job. > >It depends on what level of detail you want. I mentioned an article I i want lots of detail -- that's what gives confidence that the simulations & predictions are correct on every level. >read in Scientific American which discussed computer simulations of >the Ice Ages. Today's computers, as far as I know, do a good (but not >great) job of predicting gross effects (like the Ice Ages and >approximate global temperature distributions). They do an acceptable >job of calculating details. weather forecasters aren't helped much by their computer predictions. they still end up being right about half the time -- the same ratio one would get if one just predicted that today's weather would continue tomorrow. i think there's a long way to go towards accurate (acceptable?) predictions of detailed atmospheric effects. >In both cases the models can probably be >improved, especially as more computer power gives more accurate >models. In all cases, more power will help as long as we have the >observational detail to get data accurate enough (which means, there >is a lot of room for improvement). The statement above is just too >general. point taken... my statement may understate what current simulations can do -- but i do still contend that we have an incredibly long way to go, both in sensing and computing, before we can get very accurate predictions & understanding of at least one planetary atmosphere (ours). >: you bet. enough heat could start thermal runaway, just as enough >: CO2 could. i read in today's paper that the current guess about >: the extinction of the dinosaurs involves 3x to 5x increase in >: atmospheric CO2 levels around the time they disappeared. > >The point is, enough heat is vastly more than we are producing now >(another article said 10^-7 of the Earth's energy budget is man-made). >Enough CO2 seems not to be much more than we are producing now. we may be producing too much CO2 -- that just isn't clear yet. i think your 10e-7 number is not correct -- but i will try to find Frank Drake's notes and provide folks with some numbers of my own. his bottom line is that we will have to worry more about thermal pollution as our power needs grow. >Timescales to consider: > The atmosphere heats and cools in hours (now that I think about it, I >seem to remember deriving a cooling time for atmospheres in a course I >took on planetary science. I'll try to find this). Looking at daily >temperature curves I have estimated a time constant of no more than a >day. (i.e. the atmosphere effectively follows man-made inputs with no lag) this is interesting -- you aren't contending that the atmosphere would cool in a matter of days if the greenhouse effect caused an 1 or 2 degree temperature rise, are you? i see your point, on a local scale, at least. radiational cooling is fast. > The surface is a trickier matter, as is the ocean. I would guess the >time constant from the lag of seasons behind the driving force: the >Earth's axial tilt. The lag is slightly less than 3 months; this >would make the best-fit timescale [i.e. if one treated the earth's >temp. as a driven 2nd order system] about the same. good points. the multiple order effects (beyond 2) are a good example of aspects of the greenhouse effect or any atmospheric effect, that aren't understood that well yet...
jwm@stdc.jhuapl.edu (James W. Meritt) (03/18/88)
In article <22276@bbn.COM> eli@BBN.COM (Steve Elias) writes: >In <122@aplcomm.UUCP> jwm@stdc.jhuapl.edu.UUCP (James W. Meritt) writes: >>I believe you are confused as to my definition: I said that the greenhouse >>effect, as defined, was a confirmed, easily testable model. : : i understand your definition. it's not that tough. : i'm writing about the greenhouse effect: the scientific theory. : one which we understand more as we research and attempt to model it. As I understand it, you are discussing the applicability of a particular effect on planetary atmospheres, attempting to incorporate other influences within the model. If I am incorrect, could you please post what you are referring to when you say "greenhouse effect: the scientific theory"? We may be talking about different things, using same words, or some such..... : i'm not interested in discussing dictionary definitions of : scientific discoveries & theories. does anyone mind? Don't mind at all. Would be nice to use the same terms as everyone else when talking about the same things, though. :) >>Now, you >>are debating the applicability of the valid model to conditions under >>which is was not generated. This action is not generally recommended as >>"extrapolating beyond region of fit" also known as "going off on a limb" : thanks for telling me what i was debating. you are saying : that the greenhouse effect IS a valid model ?? I told you what I thought I was debating. I take your reaction to mean I was wrong? The greenhouse effect is a valid model. It has a well-defined,justifiable structure, measurable inputs, produces a descriptive output cabable of being used to make verifiable predictions. To me this makes it valid. just for fun: valid - well grounded or justifiable, correctly derived from premisis. How do YOU determine if a model is valid? Note: "valid", not "appropriate" nor "exhaustive" (As another aside, my masters is in operations research/systems analysis specializing in advanced modelling. I know the problems involved in validating a model.) : instead of : telling you what you were saying, i'm asking. this action : is recommended as "discussion" also known as "civil conversation". :) My statement concerning what I thought you were saying is know as "communicating": I wanted to ensure that what I thought you were saying was indeed what you meant. It is more fun to flame when you misunderstand, but you really don't learn much :( >>You are incorrect in saying that the Earth's atmosphere cannot be modeled. >>You might be more correct to say "cannot be modeled well", but you must : i said "valid model" -- meaning a model that can : actually be used to predict what the atmosphere will do: on both : macro scales and local ones. If this is your definition of "valid", what precision/accuracy do you use in determining the correctness of the prediciton? I can predict anything from nothing, but unless it correlates somewhat to reality I hasitate to call it a "valid model". Otherwise, a teacup or ouigi (sp?) board would be a valid model: they can be used to predict what the atmosphere (or anything else) will do on any scale. : we're nowhere near developing a model like this -- neither : our computation methods nor our sensing methods are up to the job. : do you concur? I do not concur on the macro scales. The meso scale models are all right, but nothing to write home about. Most of the microscale models are awful, and live in the heads of meterologist. That is why the "local forcasts" are a running joke. Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
eli@bbn.com (Steve Elias) (03/18/88)
In article <22286@bbn.COM> eli@BBN.COM (Steve Elias) writes: > weather forecasters aren't helped much by their computer predictions. ^^^^^^^^^^^^^^^^^^ oops. it's an overgeneralization again... sorry.
eli@bbn.com (Steve Elias) (03/20/88)
In <127@aplcomm.UUCP> jwm@stdc.jhuapl.edu.UUCP (James W. Meritt) writes: >The greenhouse effect is a valid model. It has a well-defined,justifiable >structure, measurable inputs, produces a descriptive output cabable of being >used to make verifiable predictions. To me this makes it valid. > >just for fun: valid - well grounded or justifiable, correctly derived >from premisis. How do YOU determine if a model is valid? >Note: "valid", not "appropriate" nor "exhaustive" i consider the greenhouse model to be just a theory -- and not proven, workable model -- because we have yet to predict and watch and atmosphere go through the greenhouse effect. we weren't around millions of years ago, when Venus MAY have gone through a thermal runaway (greenhouse effect) as we currently model it. we don't really know what happened to Venus. we also don't know whether the model for the Earth is valid, because we've yet to see any real atmospheric changes which agree with the model. my point is that a 'valid' model needs empirical results which agree with its predictions -- we don't have them yet. >(As another aside, my masters is in operations research/systems analysis >specializing in advanced modelling. I know the problems involved in >validating a model.) is empiricism involved with validating a model? (i think so). as a non-expert in advanced modelling, i'd like to know. >: "valid model" -- meaning a model that can >: actually be used to predict what the atmosphere will do: on both >: macro scales and local ones. > >: we're nowhere near developing a model like this -- neither >: our computation methods nor our sensing methods are up to the job. >: do you concur? >I do not concur on the macro scales. The meso scale models are all right, >but nothing to write home about. Most of the microscale models are >awful, and live in the heads of meterologist. That is why the >"local forcasts" are a running joke. oh well -- 2 out of 3 ain't bad... you obviously have more experience with real models, but i still think that our macro scale models will be improved a bunch over time. i wouldn't write home to Venus about any of the current models...