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Thread: Questions about Climate Science

  1. #1 Questions about Climate Science 
    Forum Freshman BenTheMan's Avatar
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    I am interested to talk to someone who really knows the global warming science, preferrably someone working in the field. (Not some hippy who's read about it on the internet.) Can anyone condense the arguments down for me, or do I have to dig through the scientific literature myself? There seems to be growing suspicion of the anthropogenic argument, and I always am weary of scientists who are also activists---i.e. a large number of climate scientists seem to be making activist/alarmist claims. At the same time, certain parts of the polar regions are changing significantly, and it seems that there ARE documentable changes occuring.

    Main questions: How do climate scientists estimate the effects of carbon and other greenhouse gases in the atmosphere? It's fairly trivial to show that carbon dioxide causes a greenhouse effect in a plexiglass box with a good thermometer, but how does this translate into a large scale system like the atmosphere?

    How do climate models work, given that the climate is a nonlinear system? That is, very small changes in initial conditions lead to drastically different final states. This tells me that the computer simultations people do are highly dubious because they are either a) based on linear dynamics, and so have nothing to do with the climate, or b) non-linear and highly dependant on initial assumptions, and therefore not very predictive. Perhaps the difference is between predicting weather and predicting climate?

    What evidence is there that the sun's power output has increased over the past century or so, resulting in the current epoch of warming? I heard some news clip on BBC about scientists disproving this, but have also seen evidence that the polar caps on Mars are also receding. Is there any validity to these claims?

    This thread is likely to dissintegrate pretty rapidly, so we should have the intelligent conversation quickly before we are overrun I just want to discuss the science of this, not the politics. If you want to discuss the politics, go to the appropriate forum, please.


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    WYSIWYG Moderator marnixR's Avatar
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    just bought "The Rough Guide to Climate Change" today
    haven't been able to start reading it yet, but looks promising at a quick glance


    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  4. #3  
    Forum Freshman BenTheMan's Avatar
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    I was hoping someone would explain everything to me so I could be lazy and not have to read a bunch of books

    There is a list a mile long of things I'd read (not related to physics) if I had time. there is an even longer list of things I have to read that ARE physics. Let me know if this book is worth reading and I will add it to my list!
    Sometimes you eat the bahr, and, well, sometimes he eats you. ---Anon
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  5. #4 Re: Questions about Climate Science 
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    Quote Originally Posted by BenTheMan
    1) Main questions: How do climate scientists estimate the effects of carbon and other greenhouse gases in the atmosphere? It's fairly trivial to show that carbon dioxide causes a greenhouse effect in a plexiglass box with a good thermometer, but how does this translate into a large scale system like the atmosphere?

    2) How do climate models work, given that the climate is a nonlinear system? That is, very small changes in initial conditions lead to drastically different final states. This tells me that the computer simultations people do are highly dubious because they are either a) based on linear dynamics, and so have nothing to do with the climate, or b) non-linear and highly dependant on initial assumptions, and therefore not very predictive. Perhaps the difference is between predicting weather and predicting climate?

    3) What evidence is there that the sun's power output has increased over the past century or so, resulting in the current epoch of warming? I heard some news clip on BBC about scientists disproving this, but have also seen evidence that the polar caps on Mars are also receding. Is there any validity to these claims?
    I will attempt to give you a response but I lay no claim to being an expert in this field. Clearly nobody's gonna explain everything to you in one post, and even if they did you'd still have to tackle the vast literature to gain a rounded understanding.

    1) There is the theoretical approach whereby you treat the atmosphere as a layered EM absorbing body of some kind (forgive me, I'm no thermodynaics whizz). You have to calculate the thermodynamic properties of the atmosphere based on the individual contributions of the constituents, and the density of the atmosphere and you find solutions to heat equations which should account for convection and radiation. Anyway, despite my inability to explain it, there is theory for this, but I'm not sure how good it is...
    There is also the palaeo approach, whereby we use "proxies" found in the ice record and the rock record to estimate past conditions. Palaeoclimatology is something that I admittedly have never studied, but I hear a lot of mention of "delta 18 O", which I believe is some kind of proxy for temperature, and there are numerous proxies for CO2 levels (which often show contradictory patterns!). One observation often shouted out by AGW skeptics is that the temperature proxies and CO2 proxies when compared in time show a clear rise in temperature followed by a rise in CO2 - there is recent work which proposes a mechanism for this, and AGW pushers have used this to suggest that we are gonna have even more CO2 then we had previously thought.

    2) As far as I am aware, a climate model is some kind of gridded (finite-difference?) model which attempts to solve the Navier-Stokes, heat, EOS, (and probably a few other) equations. Models are highly non-linear, they require artifical damping to prevent spurious sound waves, and of course a load of assumptions to actual come to some kind of numerical solution. Models can't be used to make predictions (we're talking long time scales here), although that is not their purpose as such, rather they are 'process models' designed to test hypotheses.

    3) I believe there are direct solar observations stretching back a century or so which have monitored the solar power output. I have no idea how these observations were made though, but I trust them to be reasonably accurate.
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    Forum Freshman BenTheMan's Avatar
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    Thanks for the response billiards. I do fear that eventually I will tackle some of the literature, but not soon. Maybe I'll do another PhD

    Palaeoclimatology is something that I admittedly have never studied, but I hear a lot of mention of "delta 18 O", which I believe is some kind of proxy for temperature
    Delta 18 O sounds like a change in a specific isotope of oxygen. Perhaps the more massive isotopes of oxygen are closer to the ground when the temperature is colder, which seems like an experiment with big error bars

    Wikipedia confirms it---It seems that these experiments measure the ration of oxygen isotopes---if temperatures are colder the ocean contains more O-18 and if the temperatures are warmer the ocean contains more O-16. This can probably be measured by looking at sediment deposits on the ocean floor.

    One observation often shouted out by AGW skeptics is that the temperature proxies and CO2 proxies when compared in time show a clear rise in temperature followed by a rise in CO2
    This is ok because there are other greenhouse gases, so this can't be much of an objection. Methane (I have learned) is much more potent than CO2. Maybe we are regulating the wrong emissions?

    AGW pushers have used this to suggest that we are gonna have even more CO2 then we had previously thought.
    This seems like the feedback business I've been hearing about---the temperature ``runs away'' in some sense.

    Models can't be used to make predictions (we're talking long time scales here), although that is not their purpose as such, rather they are 'process models' designed to test hypotheses.
    But the models have to be at least predictive enough to test the hypotheses? I'm confused. You make an hypothesis and then build a computer program which tests it. But the program isn't very predictive, and is based on non-linear dynamics. Maybe I am being stupid, but how is this useful? If your program isn't predictive, then it can only test your hypothesis if you've already decided what results you want? If it's nonlinear then you can't be sure that your solutions are stable?
    Sometimes you eat the bahr, and, well, sometimes he eats you. ---Anon
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    Yeah, I reckon the heavier isotope is harder to evaporate (in H20 molecule), I believe the record is in the ice which is a record of precipitation, although the interpretation of the d18O record is in disrepute at the moment (albeit at the fringes).

    I guess I can see your confusion, process models basically try to understand processes (which might be very isolated e.g. the effect of sea ice formation), as opposed to predictive models which try to tell you when and where things are going to happen. Process models do give you results, although they are not supposed to be a true prediction of reality.
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  8. #7  
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    One observation often shouted out by AGW skeptics is that the temperature proxies and CO2 proxies when compared in time show a clear rise in temperature followed by a rise in CO2
    This is both true and false. After the original rise in temperatures (Milankovitch Cycles) there is a lag of about 800 years before the CO2 levels rise, however after this period of temperature rises (not caused by CO2) the green house gases then do start to lead the temperature rises and falls.

    What evidence is there that the sun's power output has increased over the past century or so, resulting in the current epoch of warming? I heard some news clip on BBC about scientists disproving this, but have also seen evidence that the polar caps on Mars are also receding. Is there any validity to these claims?
    The suns output has remained constant for the last 60/70 years, and the last 25 years we have been able to use satellites to take the measurements which have also shown the suns output to be consistent, dropping slightly over the last 20/25 years. Mars is cooler now then it was in the 70's and the melting has only been seen on the southern ice cap over the last 3 years.

    Methane (I have learned) is much more potent than CO2
    This is true however it should be pointed out that water vapor is the most common green house gas followed by CO2 and methane. CO2 though is much more common with a current levels of 365 ppmillion and methane at 1745 ppbillion.

    ------------

    I would love for someone to comeup with an alternative idea to 'climate models'.
    Eat Dolphin, save the Tuna!!!!
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