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Sea ice minimum forecasts

Filed under: — gavin @ 17 July 2009

One of the interesting things about being a scientist is seeing how unexpected observations can galvanize the community into looking at a problem in a different way than before. A good example of this is the unexpectedly low Arctic sea ice minimum in 2007 and the near-repeat in 2008. What was unexpected was not the long term decline of summer ice (this has long been a robust prediction), but the size of 2007 and 2008 decreases which were much larger than any model had hinted at. This model-data mismatch raises a number of obvious questions – were the data reliable? are the models missing some key physics? is the comparison being done appropriately? – and some less obvious ones – to what extent is the summer sea ice minimum even predictable? what is the role of pre-conditioning from the previous year vs. the stochastic nature of the weather patterns in any particular summer?

The concentration of polar expertise on the last couple of questions has increased enormously in the last couple of years, and the summer minimum of 2009 will be a good test of some of the ideas that are being discussed. The point is that whether 2009 is or is not a record-setting or near-record setting minimum, the science behind what happens is going to be a lot more interesting than the September headline.

In the wake of the 2007 minimum, a lot of energy went in to discussing what this meant for 2008. Had the Arctic moved into a different regime where such minima would become normal or was this an outlier caused by exceptional weather patterns? Actually this is a bit of false dichotomy since they aren’t exclusive. Exceptional patterns of winds are always going to be the proximate cause of any extreme ice extent, but the regime provides a background upon which those patterns act. For instance, in the paper by Nghiem et al, they showed the influence of wind patterns in moving a lot of thick ice out of the Arctic in early 2007, but also showed that similar patterns had not had the same impact in other years with higher background amounts of ice.

This ‘background’ influence implies that there might indeed be the possibility of forecasting the sea ice minimum a few months ahead of time. And anytime there is the potential to make and test predictions in seasonal forecasting, scientists usually jump at the chance. So it proved for 2008.

Some forecasting efforts were organised through the SEARCH group of polar researchers, and I am aware of at least two informal betting pools that were set up. Another group of forecasts can be found from the Arctic ice forecasting center at the University of Colorado. I personally don’t think that the intrinsic worth of a successful prediction of overall sea ice extent or area is that societally relevant – interest in open shipping lanes that might be commercially important need much more fine-grained information for instance – but I think the predictions are interesting for improving understanding of Arctic processes themselves (and hopefully that improved understanding will eventually feed into the models and provide better tests and targets for their simulations).

What was particularly interesting about last years forecasts was the vast range of forecasting strategies. Some were just expert guestimates, some people used linear regression on past data, some were simply based on persistence, or persistence of the trend. In more mature forecasting endeavours, the methods tend to be more clustered around one or two proven strategies, but in this case the background work is still underway.

Estimates made in June 2008 for the September minimum extent showed a wide range – from around 2.9 to 5.6 M km2. One of the lowest estimates assumed that the key criteria was the survivability of first year ice. If one took that to be a fixed percentage based on past behaviour, then because there was so much first year ice around in early 2008, the minimum would be very low (see also Drobot et al, 2008). This turned out not to be a great approach – much more first year ice survived than was predicted by this method. The key difference was the much greater amount of first year ice there was near the pole. Some of the higher values assumed a simple reversion to trend (i.e. extrapolation forward from the long-term trend to 2008).

Only a couple of the forecasts used physics-based models to make the prediction (for instance, Zhang et al, 2008). This is somewhat surprising until one realises how much work is needed to do this properly. You need real time data to initialise the models, you need to do multiple realisations to average over any sensitivity to the weather, and even then you might not get a range of values that was tight enough to provide useful information.

So how did people do? The actual 2008 September minimum was 4.7 M km2, which was close to the median of the June forecasts (4.4 M km2) – and remember that the 2007 minimum was 4.3 M km2. However, the spread was quite wide. The best estimates used both numerical models and statistical predictors (for instance the amount of ice thicker than 1m). But have these approaches matured this time around?

In this year’s June outlook, there is significantly more clustering around the median, and a smaller spread (3.2 to 5.0 M km2) than last year. As with last year, the lowest forecast is based on a low survivability criteria for first year ice and I expect that this (as with last year) will not pan out – things have changed too much for previous decades’ statistical fits on this metric to be applicable. However, the group with the low forecast have put in a ‘less aggressive’ forecast (4.7 M km2) which is right at the median. That would be equal to last year’s minimum, but not a new record. It would still be well below the sea ice trend expected by the IPCC AR4 models (Stroeve et al, 2008).

There is an obvious excitement related to how this will pan out, but it’s important that the thrill of getting a prediction right doesn’t translate into actually wanting the situation to get worse. Arctic ice cover is not just a number, but rather a metric of a profound and disruptive change in an important ecosystem and element of the climate. While it doesn’t look at all likely, the best outcome would be for all the estimates to be too low.


858 Responses to “Sea ice minimum forecasts”

  1. 751
    Mark says:

    “Until NOAA and Cyrosphere today resolve these issues, I will treat their web based data products with suspicion, and will NOT cite any of their mapping/summary as an authoritative reference.

    Comment by Tim ”

    Aw.

    I bet they’re real disappointed…

  2. 752
    dave p says:

    re 704
    that was uncalled for. 100,000 sq km is a minute proportion of the melt, and could be accounted for by differing interpretations of the figures. The point being that while it would be impossible for this year and 2008 to have exactly the same ice loss the difference looks like being one for pedants.

  3. 753
    Mark says:

    “100,000 sq km is a minute proportion of the melt, and could be accounted for by differing interpretations of the figures.”

    It’s still pretty silly to say “apart from the differences, they’re the same!”.

    After all, no “differing interpretations” were taken to mean that even if the data seemed to show more ice extent (which says almost nothing about volume) was higher, that this was proof AGW is wrong, is there.

  4. 754
    Rod B says:

    Jeff (731), I don’t think that is correct; but I’m not sure, so maybe you can help.. When seawater evaporates it picks up thermal heat energy from the sea (cooling it) without (materially) increasing the temperature of the vapor. When the vapor later condenses it releases its internal energy to increase the temp up the atmosphere, but does not affect the temp or energy of the sea when the rain falls into it. Though that heated atmosphere has other possible (but not certain) routes for “returning the temperature” to the sea. Comments or corrections?

  5. 755
    Rod B says:

    Martin (742), Is there anyone who has not been treated badly at least once by a computer?? ;-)

  6. 756
    Hank Roberts says:

    Rod, no. You can’t do this without the math.
    We’ve talked this through endlessly, and you keep insisting on using words as though you could add and subtract them.

    Words like “thermal heat” and “temperature” (presumably you also have the notion there would also be nonthermal heat, or thermal cold, to fill out this bestiary?).

    You’re just fooling yourself to try to fit, I dunno what.

    Heat of condensation — molecules condense from vapor to liquid; they have quit moving too fast to stick together, and the energy goes into the surrounding atmosphere.

    Picture a lot of molecules — H2O, O2, N2 — jittering around individually. The H2O molecules start pairing off and the O2 and N2 jitter slightly more.;

    Heat of vaporization — molecules that were slow enough to stick together as liquid pick up enough energy to break loose as vapor — individual molecules.

    Picture lots of H2O molecules all together as a liquid, but something is adding to the total energy in the liquid so the mass is lurching around, the molecules are being thrown about, and eventually a crack-the-whip effect puts enough kick into one of them that it zings off independently.

    Temperature — what the thermometer reads

  7. 757
    Jeff says:

    Rod, the point I was trying to make, albeit poorly, was that latent heat transfer to the atmosphere will increase the temperature of the atmosphere, which will increase the radiant flux downward according to the Stefan Boltzmann equation. You can’t separate the effects of latent heat and downward IR flux, so it is foolhardy to compare the magnitudes of latent heat (one way) and net radiative flux (two ways). Besides, BobFJ stated that latent heat represented the greatest heat loss PROCESS, which is not true, for the reasons I have mentioned above.

  8. 758
    dave p says:

    Re 754 where did you get that bit about AGW being wrong, without it the extent would be near it’s 1979 level.All it means is that the melting is similar to last years and above 2007. The 2007 low will remain an anomaly at least until next year.

  9. 759
    BobFJ says:

    Barton Paul Levenson 737, in part:

    Sunlight and atmospheric back-radiation HEAT the surface.

    So the backradiation heating that you refer to replaces a goodly portion of the heat that is lost? Yes or no?

    IR radiation from the ground, conduction/convection, and evapotranspiration COOL the surface.

    Agreed, but you also wrote:

    Both numbers are equal over the long run. By your definition, that would mean no heat is being transferred.

    If you mean that the K & T upwelling EMR of 396 w/m^2 and the backradiation of 333 w/m^2 are equal over the long run, then you are contradicting K & T 1987, and various divisions of NASA.

    Sorry, but you can’t say evapotranspiration cools the surface and infrared radiation doesn’t. That’s just illiterate from a physics point of view.

    I’ve never said that, and for instance in my 730, quote: The net HEAT loss via EMR is (396 – 333)

  10. 760
    PeterMartin says:

    I must say that you are extraordinarily patient with people like Max.
    But they are a big distraction to those of us who are generally interested in the science and maybe have a few questions of our own. Max is of the belief that ‘puny man’ is incapable of changing the Earth’s climate and that it is ‘arrogant’ to think otherwise. This kind of belief can’t be rational. It must therefore be delusional, and needs to be treated as such.

  11. 761
    manacker says:

    PeterMartin
    (also known as Tempterrain)

    Rather than opining to third parties on what you believe my opinion may be, why don’t you stick to your own?

    There is a lot to be learned about our planet’s climate and possible human plus cyclical natural impacts and a myopic fixation on just either of these factors would be foolish, as I am sure you would agree.

    That is what makes exchanges on sites such as RC interesting. One can always learn something new if one keeps an open mind.

    Max

  12. 762

    manacker writes:

    Here is some “empirical evidence” from the cited Minschwaner + Dessler report (Fig. 7), showing observed water vapor increase with warming and comparing this with the “constant RH assumption” line as well as with the line from the simplified M+D model.
    http://farm4.static.flickr.com/3347/3610454667_9ac0b7773f_b.jpg

    Looks pretty clear to me. This evidence shows that you are wrong, but let’s not belabor that point.

    Right, max, a study confined to +/- 20 degrees latitude, with restrictions on areas used by observed OLR, over six years of time series data, with a one-month time lag used for no clear reason (to make the correlation higher?) disproves all the studies using global data over longer periods of time and without the artificial restrictions.

    Can’t you read?

  13. 763

    BobFJ writes:

    If you mean that the K & T upwelling EMR of 396 w/m^2 and the backradiation of 333 w/m^2 are equal over the long run, then you are contradicting K & T 1987, and various divisions of NASA.

    I am not saying that. I am saying:

    Heating:
    161 Solar
    367 Atmospheric back-radiation

    468

    Cooling:
    371 IR radiation
    80 latent heat
    17 sensible heat

    468

  14. 764
    Mark says:

    “That is what makes exchanges on sites such as RC interesting. One can always learn something new if one keeps an open mind.”

    That isn’t what you’ve said elsewhere, Max.

    Speaking from both sides of your face…

  15. 765
    manacker says:

    Barton Paul Levenson

    Empirical evidence for water vapor RH decreasing significantly with increased temperature over the tropics. Can’t you read?

    What percentage of the world’s surface would you guess is covered by +20 / -20?

    Take a guess and ry to be a bit more polite.

    Max

  16. 766
    manacker says:

    Gavin

    Thanks for your comment (746) on “observed empirical data” versus “computer model outputs (or ‘results’)” as tangible support for hypotheses or theories.

    You wrote:
    “They [computer model results] do [provide tangible support for hypotheses or theories] when they provide a match between observed effects and model results – implying that physical causes and effects can be attributed.”

    I think we are saying the same thing, Gavin. It is the “observed empirical data” that lend the “computer model results” their authenticity. Without the match with “observed empirical data”, the “computer model results” per se do not provide tangible support for hypotheses.

    That was the point I was trying to make.

    Max

  17. 767
    CTG says:

    Re 766. And yet, Max, you continue to insist, after 20 times of being told otherwise, that constant relative humidity is an assumption of the models, rather than a result.

    Can we take it from this latest pronouncement that you have finally learnt this distinction?

    Yeah, right.

  18. 768
    manacker says:

    CTG (767)

    You are making a big “to-do” about a fine point in semantics when you write:

    “And yet, Max, you continue to insist, after 20 times of being told otherwise, that constant relative humidity is an assumption of the models, rather than a result.”

    First, please show the “20 times”, CTG.

    Second, as Gavin has commented, a “result” (or climate model output) is only valid as tangible support for a hypothesis or theory if it is backed by empirical evidence.

    M+D have provided empirical evidence, based on actual physical observations, that RH does nor remain constant with warming but that water vapor increases by only a small fraction of what would happen if RH remained constant. This study was limited to the tropics (+20 to –20 degrees).

    Model “results” that predict constant RH with warming are based on “assumptions” that are fed in.

    I have seen no empirical evidence that RH remains constant with warming.

    Show me the empirical evidence that RH remains constant with warming, CTG.

    Max

    [Response: Soden et al (2002; 2005),Forster and Collins (2004), Bauer et al (2004), Dessler and Sherwood (2009), Allen et al (2003), McCarthy and Toumi (2004). All taken from IPCC AR4 section 8.6.3.1. - gavin]

  19. 769
    Mark says:

    “Take a guess and ry to be a bit more polite.

    Max”

    Try being less dumb.

    Annoying people tends to make them less polite to you.

  20. 770
    Hank Roberts says:

    > +20 / -20?

    Max. You keep ignoring the problems — here, the six month time lag, Max; if you move any line on a chart around far enough you can match up something similar from earlier. Just slide one over the other til you see something line up and claim a correlation with a time lag.

    Your routine continues: proclaiming your conclusion; people point out whatever source you claim doesn’t support your story; you repeat it.

    You can’t be reading the science and be this wrong this consistently.

    Are you just channeling CO2Science? Where are you getting this stuff?

    People are being incredibly patient.

  21. 771
    manacker says:

    Hank Roberts

    Sorry, your last post (770) does not appear to make sense.

    Can you express this all a bit more clearly?

    Thanks.

    Max

  22. 772
    Mark says:

    Max your question #771 doesn’t make sense.

    Can you please explain your confusion better so you may be answered.

    Thanks.

  23. 773
    Rod B says:

    Hank, not sure of your complaint as I agree with most of your words (756). Maybe the disagreement is in the semantics: you might have it down cold but there is a great confusion out there with the terms “heat” energy” and “temperature”. Temperature and energy are not equivalent; heat is more often than not (an) energy but not temperature; though sometimes it does refer to temperature (something getting hot by adding “heat”). Ergo confusion. So I try to pick my terms carefully here.

  24. 774
    t_p_hamilton says:

    Max said:Second, as Gavin has commented, a “result” (or climate model output) is only valid as tangible support for a hypothesis or theory if it is backed by empirical evidence.”

    See Gettelman and Fu (2008) as well
    http://www.cgd.ucar.edu/cms/andrew/papers/gettelman2008_wv.pdf

    Since this paper (in addition to the older ones available for IPCC AR4) shows agreement between empirical evidence and modelling, by your standards it is valid support for the theory. Your misunderstanding was merely due to an incomplete survey of the literature. Perhaps you should change your approach so that you don’t miss these papers.

  25. 775
    Rod B says:

    Jeff (757), I understand that. The IR “return” is one thing I had in mind in my “other routes”. (Sidebar: there is some confusion/disagreement over the atmosphere generating S-B radiation.) I’m not sure if I agree with you viz-a-viz BobF, though that whole thing strikes me as entirely semantic.

  26. 776
    Rod B says:

    dave p (758), did you mean re 704, not 754??

  27. 777

    Back to ice:

    http://seaice.bplaced.net/buoy-pos/

    I wonder if the Bremen people can be kind enough (as they always are) to show us a link to their splendid up to date websites… Namely the buoy animations as the link above and model volume estimates.

    And the very quiet Los Alamos people: they would be kind to show the CICE projections… I want to see if sea current appears to change over time.

  28. 778

    http://iabp.apl.washington.edu/animations/Rigor&Wallace2004_AgeOfIce1979to2007.mpg

    This site from international Buoy program shows a nice but too fast animation to see if there is a dramatic current change. http://iabp.apl.washington.edu/research_seaiceageextent.html
    Has a few explanations

  29. 779
    manacker says:

    t_p_hamilton

    I’m checking out your 774 and will get back to you.

    Max

  30. 780
    CTG says:

    “First, please show the “20 times”, CTG.”

    Now who’s being pedantic? I don’t know the exact number of times that Gavin has corrected you on this, but any number greater than 1 indicates that you are being obtuse on this point. There are many times when you have claimed the GCMs must be wrong because they assume constant relative humidity. Do you deny you have said this?

    There is a great deal of difference between an assumption and a result, as Gavin has explained several times. An assumption of constant relative humidity would mean that the models take one value for RH at the start, and never vary it. This is not what they do. RH is in fact a calculated product of the models. Specific humidity can change by a large amount (i.e. water vapour feedback), whilst relative humidity changes by a much smaller amount. Relative humidity changes by such a small amount that you can approximate it to be constant

    Gavin has also provided you with a list of references – these have the empirical evidence you are looking for. Cooling following volcanic eruptions shows large changes in specific humidity, while relative humidity stays roughly constant. In fact, if the models do not include the water vapour feedback mechanism, they are unable to reproduce the cooling induced by volcanic eruptions.

    The information is there if you look for it, Max, but if you are unwilling to read the actual science and learn from it, there is nothing we can do to help you.

  31. 781
    CTG says:

    You see, Max, your behaviour over this relative humidity business is one of the main reasons people here have little time for you.

    It is not unreasonable for a skeptic to ask questions, and indeed that should be encouraged. It is unreasonable, though, for a skeptic to refuse to accept an answer to a question just because they don’t like the answer.

    For example:
    Reasonable Skeptic: I think the GCMs are wrong because they assume constant relative humidity.
    Gavin: Actually, constant RH is a result of the models, not an assumption. Here are some references.
    [RS goes away and reads the references]
    Reasonable Skeptic: Oh right, my mistake. Next question…
    [RS never mentions constant RH being an assumption again].

    Compare that with:
    Max: I think the GCMs are wrong because they assume constant relative humidity.
    Gavin: Actually, constant RH is a result of the models, not an assumption. Here are some references.
    [a few posts later...]
    Max: I think the GCMs are wrong because they assume constant relative humidity.
    [repeat ad nauseam]

    Do you see the difference, Max?

  32. 782
    PeterMartin says:

    Max,

    Are you lecturing us on keeping an open mind? Nice one!

    Your earlier comment, to which I was referring, was “The arrogance of thinking that puny man is changing global climate is only exceeded by the stupidity of believing we can – and must – urgently do something to stop it”

    This sort of declaration cannot be based on any sort of rationalaty. The rational response to an initial question of “is it possible that mankind is changing the climate?” is to say “Yes maybe it is. Lets do some calculations and look at the evidence”.

    You obviously decided that this was not at all any kind of necessary step. That’s not keeping an open mind!

    Its not good to stifle debate, but I would like the guys at real climate to stick to Climate Science rather than having to waste time with people who hold irrational beliefs.

  33. 783
    dave p says:

    the Bremen site seema to be having delays updating. anybody know why?

  34. 784

    Max,

    The behavior of RH in a warming climate is really simple, and it’s related (I’m pretty sure …) to the shape of the pH20 v T curve for a given RH.

    Put into plain English, with fewer abbreviations, the amount of moisture that warm air holds is greater than the amount of moisture that cold air will hold. But it isn’t just “greater”, it’s “more greater” — the amount of water vapor air can hold at a fixed relative humidity increases at a faster rate than the temperature (positive second derivative, if you know what that means). What this means is that as the air cools in the evening, the relative humidity increases faster, and this increases the probability that the water vapor will come out as precipitation. So, back down goes the relative humidity.

    This is what an earlier poster said about a warming climate increases the “velocity” or “turnover rate” of water vapor in the atmosphere. The higher daily temperatures INCREASE evaporation, which increases the total water vapor. But the swing back from those higher temperatures have a greater impact on forcing that water vapor back to the liquid state than at lower temperatures. The result — constant relative humidity and it doesn’t even require a model.

    Here’s an equation (actually, a Java method …) that might make it easier to understand –

    /**
    * pH2O – compute the H2O saturation partial pressure for a given
    * temperature (in degrees C) using the Magnus-Teton formula.
    *
    * @param temp
    * @return pH2O.
    */
    private static double pH2O(double temp) {
    double value = ((17.625 * temp) / (243.04 + temp));
    value = 6.1094 * Math.exp(value);
    return value;
    }

    (We’ll see if the “pre” tags are honored!)

    As you can see, pH2O increases EXPONENTIALLY with increases in temperature, but decreases EXPONENTIALLY with decreases from those same higher temperatures.

    What then is “Relative Humidity”? It’s the ratio of the dewpoint’s pH2O with the current temperatures pH2O at saturation. Again, more Java (all of which is copyrighted by me, but since I’m not copying the entire file, feel free to print out and line your bird cage with) –

    public static double estimateRH(double dewPoint, double temp) {
    if (temp < dewPoint)
    return 100;

    double currentPH2O = pH2O(temp);
    double dewPH2O = pH2O(dewPoint);

    return (dewPH2O / currentPH2O) * 100;
    }

    As you should be able to see (maybe …) the rise in the dewpoint caused by rising temperatures (which would normally cause a rise in RH) is offset by the newer, higher temperatures.

  35. 785
    Jeffrey Davis says:

    I don’t understand the issue under discussion. In a local weather report, relative humidity goes up and down almost hourly. Is this a case where words mean something differently in a technical context than in the vernacular?

  36. 786
    PeterMartin says:

    Furrycatherder, This is all good stuff. If Max has brought this out, then maybe he does have a role to play after all. If you think he is unreasonable on RC, though he’s actually on his best behaviour, you should see what he’s like on other forums. He’s pretty active. I really don’t know how he finds time for the normal things in life.

    Max’s latest words of wisdom, on the topic of Secretary-General Ban Ki-moon’s warning on the urgency to act to cut GHG emissions is “FIRE THE BUM !”. So, unfortunately, his level of irrationality puts him beyond all help.

  37. 787

    #761 manacker

    Max

    PeterMartin has made some cogent points regarding your perspective. Rather than saying your version of ‘I know you are but what am I’, might you consider the points he is clearly making are actually reasonable assessments of your perspective in that you have presented many of your considerations out of context.

    I also agree with PeterMartin that you do not seem to have a reasonable open mind in this subject area.

  38. 788

    #766 manacker

    Do you live in a cherry orchard? I’ve looked now a little at what you are posting elsewhere, hmmm… pot, meet kettle.

    Here, manacker cherry picks his way through the IPCC
    http://wattsupwiththat.com/2009/03/01/hansens-coal-and-global-warming-protest-may-get-snowed-out/

    Here manacker and Bob_FJ cherry pick their way through temp data and even using an admission of fact regarding short term data v. long term trend from IPCC Chairman

    http://www.paulmacrae.com/?p=74

    The point is Max, you are looking at everything out of context. That is foolish actually. You have been shown relevant context and you ignore it. That is foolish as well. Maturity is not making the same mistake over and over, especially in the face of relevant reason and overwhelming evidence.

    Why is it you can’t separate short term from long term? Is it that you can’t understand that natural variability actually exists on a short term and decadal scale within the 30 year trend that already has attribution?

    When I here you speak of having an ‘open mind’ I am again reminded of a line form the movie ‘Princess Bride’ – “Do you think he is using the same wind we are using?”

    In this case, I don’t think you are using the same wind. I would venture that scientists use as their wind ‘ratiocination’ and the ‘scientific method’ and you are using for your wind something akin to, or same as, ancient mythology, naivete, and portions of myopia and ignorance.

  39. 789
    manacker says:

    FurryCatHerder

    Good analysis. What about the role of clouds? Will these increase with higher RH in the complex environment of our atmosphere? What impact will this have? Will there be more (or less) precipitation? What impact will this have? How will all these changes be felt locally, regionally and globally?

    Theory is great (Clausius-Clapeyron, etc.). But our climate is far more complex than simple gas laws.

    Max

  40. 790
    manacker says:

    Peter Martin

    Since you are repeating messages that you posted on another site, I will repeat the response I gave you to this message on another site.

    I usually do not enter into a discussion based on a loaded question, but I will make an exception here, since I believe that you are seriously interested in my answer rather than than just baiting me.

    You asked: “Why do you believe that ‘puny man’ is incapable of changing the climate? Why is it ‘arrogant’ to suggest otherwise?”

    Several world politicians (including Germany’s Angela Merkel) have made statements such as “we must stop global warming to no more than 2°C by year 2100”.

    It is “arrogant” of these politicians to believe that they can actually achieve this self-imposed goal.

    IPCC tells us that CO2 is likely to be at a level twice the pre-industrial level of 280 ppmv by year 2100 (560 ppmv).

    IPCC also tells us that this will cause an equilibrium warming of 1.5 to 4.5°C above pre-industrial values by year 2100. The mean 2xCO2 climate sensitivity is stated to be 3.2°C.

    So far it has warmed by around 0.7 to 1.0°C since pre-industrial times. Some AGW gurus tell us that some of the warming to date is “still in the pipeline”.

    This means that (on average) we have somewhere between 2.2 and 2.5°C warming to be expected from AGW from today until year 2100 (all other things being equal, which they rarely are).

    And these politicians are telling us that they will commit to keeping this at a maximum of 2.0°C!

    No big deal. Just (pardon the expression) “hot air”.

    Now let’s look at some specific proposals to “change our planet’s climate.

    Hansen (a climate “prophet”, who happens also to be quite “arrogant”), tells us that coal trains are like the “death trains” of WWII, and that 450 ppmv is a “dangerous level” of CO2, which could lead to irreversible “tipping points” in our climate and horrible consequences for our society and our environment.

    From this horror scenario have come proposals that the USA should stop building new coal-fired power plants in starting in 2010 and shut down half of all existing plants by 2050.

    Now, I have figured out what impact this astronomically costly upheaval of US power generation would have on global temperature, and it is around 0.05°C. (You and I discussed this earlier on the Harmless Sky site).

    So yes. “Puny man” (the politicians and climate gurus, included) is unable to “change the climate” on our planet, Peter.

    Hope this answers your question.

    Max

  41. 791
    manacker says:

    CTG

    You appear to misunderstand the exchange on RH.

    We are at the point now that I have presented one study based on empirical evidence of physical observations, which shows that water vapor content increases with warming, but only at a small fraction of the rate required to maintain a constant RH. This study (M+D) was limited to the tropics.

    In addition, I have posted long-term NOAA data that show that absolute atmospheric water vapor content as measured by weather balloons and satellites (and hence also RH) have decreased over the long term, despite increasing global temperatures over this period.

    Gavin has cited other studies, which purport to provide empirical data based on physical observations, which show that RH remains constant with warming.

    I have not yet checked out all these references to make sure that they are, indeed, based on the empirical data gleaned from actual physical observations and not simply on model studies.

    Once I have looked at them all in detail, I will come back to this discussion.

    Got it now?

    Max

  42. 792

    manacker writes:

    Empirical evidence for water vapor RH decreasing significantly with increased temperature over the tropics. Can’t you read?

    What percentage of the world’s surface would you guess is covered by +20 / -20?

    Take a guess and ry to be a bit more polite.

    Since a perfect sphere has area inside a given latitude of sine theta, 34%. But aside from exclusing two-third of the world, you’re ignoring the fact that climate conditions vary greatly by latitude. And all the other special conditions the folks writing your article listed in the very chart you referred me to. And why do you focus on that one study and ignore the four studies I referred you to?

    Could it be because you’re only looking for evidence to support a predetermined viewpoint, and ignoring anything that doesn’t fit?

    [Response: Don't forget that M&D are only looking at a very small chunk of the upper troposphere around 200 to 100mb, (around 15km height). - gavin]

  43. 793

    Jeffrey Davis writes:

    In a local weather report, relative humidity goes up and down almost hourly. Is this a case where words mean something differently in a technical context than in the vernacular?

    The reference is to the global average, which seems to stay about the same over significant differences in temperature.

  44. 794

    Max @ 790:

    From this horror scenario have come proposals that the USA should stop building new coal-fired power plants in starting in 2010 and shut down half of all existing plants by 2050.

    Now, I have figured out what impact this astronomically costly upheaval of US power generation would have on global temperature, and it is around 0.05°C. (You and I discussed this earlier on the Harmless Sky site).

    Well, by 2050, most of the existing coal plants will long since have reached their end-of-life and need replacing anyway. Why not replace them with something that doesn’t require cutting the tops off mountains or digging giant holes in the ground?

    Reality is that renewable energy really does work. It’s cheap, abundant, improves the quality of life (my friends are turning their thermostats up because of huge bills, I’ve turned mine down and I still average $47 a month — and that includes recharging an electric vehicle) and doesn’t pollute. You can support getting rid of coal because it causes global warming, or you can support getting rid of coal because renewable energy makes life better. All I know is that while people I know here in Austin, TX are fretting huge electric bills and rising gasoline prices, I’m just sitting here shaking my head.

  45. 795

    Max @ 789:

    FurryCatHerder

    Good analysis. What about the role of clouds? Will these increase with higher RH in the complex environment of our atmosphere? What impact will this have? Will there be more (or less) precipitation? What impact will this have? How will all these changes be felt locally, regionally and globally?

    Uh, what higher relative humidity? Did you just completely ignore what I wrote? The only thing that’s going to be higher is the absolute humidity, and that doesn’t affect clouds. Clouds happen when air is saturated, and at higher average temperatures, air holds more water before saturation (I even gave you the formula), so fewer clouds. The water vapor that is in the air further contributes to warming (ever noticed that a humid night is a warmer night?), but we don’t wind up living on some cloud-covered planet that reflects all the sun’s radiation magically back into space because the increased warming due to increased water vapor leads to … a greater ability to hold more water vapor.

    Look, if you want to be a “skeptic”, that’s fine — but try to understand what the heck is going on.

    And for an added bonus, if you’re just here to cause trouble, find ways to cause trouble and actually be RIGHT. Because causing trouble and being wrong is just boring. But causing trouble and being right — much more exciting.

  46. 796

    Jeffrey Davis @ 785:

    I don’t understand the issue under discussion. In a local weather report, relative humidity goes up and down almost hourly. Is this a case where words mean something differently in a technical context than in the vernacular?

    Relative humidity rises and falls because the amount of water vapor in the atmosphere doesn’t rise and fall as rapidly as the temperature. But what holds it all “up” is the dew point, which is the basis for the relative humidity.

    All relative humidity is is the percentage difference between the amount of water the atmosphere COULD hold at the present temperature, and the amount of water the atmosphere DOES hold. As the temperature rises, the relative humidity falls because the dew point hasn’t changed. In the evening, the temperature falls and the relative humidity rises because the dew point still hasn’t changed. Of course, rain, evaporation and air moving in from somewhere else can change that, but that complexity is what makes life worth living.

  47. 797

    #790 manacker

    The message you are stating in this post is completely bizarre. In other posts you doubt that man is changing the climate and here you are using the statements of others that say man ‘has’ changed the climate but ‘now’ we ‘can’t’ change the climate.

    When considered together your spin is cumulative and increasingly foolish. Also, you bait all the time and you refuse to answer questions that ‘bait’ you? Hypocrisy is the word that best describes your behavior.

    So let’s add your inferred perspectives together:

    - Climate is too complex to understand.

    - The people you quote arrogantly claim man has changed the climate.

    but if man has changed the climate

    - It is arrogant of the people you quote to claim that man can change the climate (mitigation).

    Of course, you are still cherry picking form the solution bin just to create a strawman you can burn down to make your point. There are many other possibilities in mitigation such as efficiency and consumption reduction as well as biomass production for energy and carbon capture. etc. etc.

    SUMMARY
    I conclude that either you are here to confuse others by making nonsensical arguments, or you have no clue what you are talking about, or likely/possibly some combination of the two.

    PS Wouldn’t it be amazing if you were held accountable for misinformation and misdirection.

    PPS Pot, meet kettle.

  48. 798
    CTG says:

    Re #791
    Ah yes, shift the goalposts. I take it you now accept that GCMs do not assume constant RH, then? Good, at least that’s progress.

    As to empirical evidence, yes the references Gavin gave you do include empirical evidence.

    You, on the other hand, quote Minschwaner & Dessler, the abstract of which says:

    “The sensitivity of water vapor in the tropical upper troposphere to changes in surface temperature is examined using a single-column, radiative–convective model”.

    I’m sorry, but how exactly does this contradict the finding of constant RH in global GCMs looking at the whole atmosphere?

    You have not provided one piece of evidence that supports your claim that GCMs assume constant RH.

    You have not provided one piece of evidence that RH cannot remain constant in the presence of warming/cooling.

    Gavin has provided several pieces of evidence to the contrary, and you say you’ll get back to us later…

    Can’t wait.

  49. 799
    manacker says:

    John P. Reisman

    The question was whether or not man could change the climate on Earth, and I simply stated that the plan of stopping new coal-fired plants in the USA after 2010 and shutting down half of the existing ones by 2050 would only result in a theoretical reduction of temperature by 2050 of 0.05 degrees C.

    The least expensive way to do this would be to replace the coal-fired capacity with new nuclear fission plants. Maybe by 2050 the “fast breeder” technology with thorium could be an alternate to minimize the spent fuel problem. Maybe there might even be commercial nuclear fusion by then. Who knows?

    Saving energy and increasing efficiency, where possible, is a given, of course, as are the development of more efficient electrical cars, trucks, etc.

    Whether wind and solar sources will ever be able to overcome the fact that neither has a better on-line factor than around 30% is questionable, but bio-fuels may have some promise. Ethanol from sugar cane works well in Brazil (but the rain forests suffer if this is where the sugar cane will be grown); ethanol from corn has been a disaster in the USA, driving up food prices in the process.

    I have not seen any other specific “mitigation” plans (carbon taxes or cap and trade schemes will not result in any reduction of temperature increase, as we all know).

    Let’s say some of the solar experts are right, and we are headed for another Maunder minimum, with temperatures well below the late 20th century levels. What will man be able to do to change this climate fluctuation?

    My point is simply that we are not able to change things very much, no matter what we do.

    This is not based on “cherry picking a solution” (as you have stated). It is simply evaluating one of the specific solutions that has been proposed and establishing that it will have no effect on our climate.

    If you have some specific plans that could change our climate, please lay them out, with a calculation of just how much reduction in atmospheric CO2 the plans will achieve, so the net reduction in temperature of the plan can also be evaluated. Along with this, the cost of the proposed plan (investment as well as running cost) should be considered, so we can see waht the unit CO2 ppm cost and unit temperature cost will be.

    Max

  50. 800
    manacker says:

    CTG

    You asked: “I take it you now accept that GCMs do not assume constant RH, then?”

    What change in RH do they assume then, CTG? An increase? A decrease?

    Please try to be specific.

    Max


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