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Updates to model-data comparisons

Filed under: — gavin @ 28 December 2009 - (Italian)

It’s worth going back every so often to see how projections made back in the day are shaping up. As we get to the end of another year, we can update all of the graphs of annual means with another single datapoint. Statistically this isn’t hugely important, but people seem interested, so why not?

For example, here is an update of the graph showing the annual mean anomalies from the IPCC AR4 models plotted against the surface temperature records from the HadCRUT3v and GISTEMP products (it really doesn’t matter which). Everything has been baselined to 1980-1999 (as in the 2007 IPCC report) and the envelope in grey encloses 95% of the model runs. The 2009 number is the Jan-Nov average.

As you can see, now that we have come out of the recent La Niña-induced slump, temperatures are back in the middle of the model estimates. If the current El Niño event continues into the spring, we can expect 2010 to be warmer still. But note, as always, that short term (15 years or less) trends are not usefully predictable as a function of the forcings. It’s worth pointing out as well, that the AR4 model simulations are an ‘ensemble of opportunity’ and vary substantially among themselves with the forcings imposed, the magnitude of the internal variability and of course, the sensitivity. Thus while they do span a large range of possible situations, the average of these simulations is not ‘truth’.

There is a claim doing the rounds that ‘no model’ can explain the recent variations in global mean temperature (George Will made the claim last month for instance). Of course, taken absolutely literally this must be true. No climate model simulation can match the exact timing of the internal variability in the climate years later. But something more is being implied, specifically, that no model produced any realisation of the internal variability that gave short term trends similar to what we’ve seen. And that is simply not true.

We can break it down a little more clearly. The trend in the annual mean HadCRUT3v data from 1998-2009 (assuming the year-to-date is a good estimate of the eventual value) is 0.06+/-0.14 ºC/dec (note this is positive!). If you want a negative (albeit non-significant) trend, then you could pick 2002-2009 in the GISTEMP record which is -0.04+/-0.23 ºC/dec. The range of trends in the model simulations for these two time periods are [-0.08,0.51] and [-0.14, 0.55], and in each case there are multiple model runs that have a lower trend than observed (5 simulations in both cases). Thus ‘a model’ did show a trend consistent with the current ‘pause’. However, that these models showed it, is just coincidence and one shouldn’t assume that these models are better than the others. Had the real world ‘pause’ happened at another time, different models would have had the closest match.

Another figure worth updating is the comparison of the ocean heat content (OHC) changes in the models compared to the latest data from NODC. Unfortunately, I don’t have the post-2003 model output handy, but the comparison between the 3-monthly data (to the end of Sep) and annual data versus the model output is still useful.


Update (May 2012): The graph has been corrected for a scaling error in the model output. Unfortunately, I don’t have a copy of the observational data exactly as it was at the time the original figure was made, and so the corrected version uses only the annual data from a slightly earlier point. The original figure is still available here.

(Note, that I’m not quite sure how this comparison should be baselined. The models are simply the difference from the control, while the observations are ‘as is’ from NOAA). I have linearly extended the ensemble mean model values for the post 2003 period (using a regression from 1993-2002) to get a rough sense of where those runs could have gone.

And finally, let’s revisit the oldest GCM projection of all, Hansen et al (1988). The Scenario B in that paper is running a little high compared with the actual forcings growth (by about 10%), and the old GISS model had a climate sensitivity that was a little higher (4.2ºC for a doubling of CO2) than the current best estimate (~3ºC).

The trends are probably most useful to think about, and for the period 1984 to 2009 (the 1984 date chosen because that is when these projections started), scenario B has a trend of 0.26+/-0.05 ºC/dec (95% uncertainties, no correction for auto-correlation). For the GISTEMP and HadCRUT3 data (assuming that the 2009 estimate is ok), the trends are 0.19+/-0.05 ºC/dec (note that the GISTEMP met-station index has 0.21+/-0.06 ºC/dec). Corrections for auto-correlation would make the uncertainties larger, but as it stands, the difference between the trends is just about significant.

Thus, it seems that the Hansen et al ‘B’ projection is likely running a little warm compared to the real world, but assuming (a little recklessly) that the 26 yr trend scales linearly with the sensitivity and the forcing, we could use this mismatch to estimate a sensitivity for the real world. That would give us 4.2/(0.26*0.9) * 0.19=~ 3.4 ºC. Of course, the error bars are quite large (I estimate about +/-1ºC due to uncertainty in the true underlying trends and the true forcings), but it’s interesting to note that the best estimate sensitivity deduced from this projection, is very close to what we think in any case. For reference, the trends in the AR4 models for the same period have a range 0.21+/-0.16 ºC/dec (95%). Note too, that the Hansen et al projection had very clear skill compared to a null hypothesis of no further warming.

The sharp-eyed among you might notice a couple of differences between the variance in the AR4 models in the first graph, and the Hansen et al model in the last. This is a real feature. The model used in the mid-1980s had a very simple representation of the ocean – it simply allowed the temperatures in the mixed layer to change based on the changing the fluxes at the surface. It did not contain any dynamic ocean variability – no El Niño events, no Atlantic multidecadal variability etc. and thus the variance from year to year was less than one would expect. Models today have dynamic ocean components and more ocean variability of various sorts, and I think that is clearly closer to reality than the 1980s vintage models, but the large variation in simulated variability still implies that there is some way to go.

So to conclude, despite the fact these are relatively crude metrics against which to judge the models, and there is a substantial degree of unforced variability, the matches to observations are still pretty good, and we are getting to the point where a better winnowing of models dependent on their skill may soon be possible. But more on that in the New Year.


906 Responses to “Updates to model-data comparisons”

  1. 651
    Tilo Reber says:

    Doug:
    “November 2009 had the third-lowest average extent for the month since the beginning of satellite records. The linear rate of decline for the month is now 4.5 percent per decade.”

    I’m not sure what your attachmet to November is Doug, but I think that this chart is more informative.

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg

    It shows very low levels of sea ice for most of 2007 and some degree of recovery since. As I said above, I don’t know if that indicates stabilization is taking place due to the fact that the surface temperature hasn’t continued to warm – but it may. We need a few more years to tell.

    Doug:
    Is “I have a hard time believing” supposed to substitute for a coherent argument?

    Well, Doug, I do the best I can, but if you have a coherent argument for why the ice can get thinner without the surface area getting smaller I would like to hear it.

    My argument is this: The ice is generally thicker at the poles than away from them. And the water is generally warmer away from the poles than at the poles. So, for example, if you remove one meter of sea ice at the pole, then removing that same meter or more at the edges would reduce the thickness to zero. When it is zero, the sea ice area is shrunken.

    Do you want to argue that you can remove ice thickness from the pole without also removing it from the edges?

    I think that there has to be a very close correlation between thickness and area. But if you don’t, then please give me your coherent argument.

  2. 652
    Doug Bostrom says:

    Tilo Reber says:5 January 2010 at 1:54 AM

    I’ll stick with November, but you can pick any month you like.

    Can you show me the “recovery” in this?

    http://nsidc.org/images/arcticseaicenews/20091207_Figure3.png

    Where is the recovery, Tilo?

    Your stage business about thickness versus extent is potentially distracting, but first you have to explain the “recovery” bit.

  3. 653
    Tilo Reber says:

    JasonB #643
    “Anyway, I don’t see how you can deduce that “the rest of the planet isn’t changing at all”. Here in Australia we’ve just experienced our second-hottest year on record.”

    I’m not sure how Australia is relevant, Jason. I’m deducing that the rest of the planet isn’t changing at all from this:

    http://4.bp.blogspot.com/__VkzVMn3cHA/SQkAxK2k6CI/AAAAAAAAADs/F4NlhqTzFgM/s1600-h/U+11+Year+Temp+Data.bmp

    It tells me two things. The trend since 1998 has been relatively flat – at least through 2008. The divergence by GISS is about .1C per decade. Slightly more from the satellites. This is half of the predicted IPCC decadal warming due to CO2. I consider that significant. In any case, that chart is now a year out of date and we have had a warm 2009. But I don’t think that the divergence has changed. The place where I started into this discussion was about getting and ENSO updated version of HadCrut3. The one that went through last year showed this:

    http://1.bp.blogspot.com/__VkzVMn3cHA/SHLOM1k5XJI/AAAAAAAAADE/u7AlyoBk0EU/s1600-h/ENSO+Adjusted+HadCrut3v+Data.bmp

    My expectation is that when we include 2009 and ENSO adjust it we will still be relatively flat. Hopefully that explains why I think that the rest of the planet isn’t changing at all.

    “Perhaps because you aren’t aware that one of the key fingerprints of AGW that distinguishes it from other potential sources of warming is stronger polar warming?”

    Actually, I am aware of that. But if it’s stronger than the warming across the rest of the globe, what do we get when we multiply zero. And in regards to that effect causing divergence, why wasn’t it causing it in the 70s, 80s, and 90s?

    JasonB:
    “This is an a-priori logical reason for preferring GISS”

    And I agree that it is a good reason. But when other sources diverge, you need to look at the sensibility of the divergence. Saying that it all comes from the small areas at the pole is not sensible to me for the reasons that I gave above.

  4. 654
    JasonB says:

    I wrote: “However, in this particular instance, I would not advocate its use. Fortran is a domain-specific language and this is its domain. C doesn’t compete well with Fortran when it comes to numeric code, and even C++ needs all sorts of advanced tricks (my favourite being expression templates — absolutely brilliant)”

    648, dhogaza:

    “Of course the whole point of being a compiler writer – which I was for about twenty years – is that the “absolutely brilliant” comments should be the domain of compiler optimization. If you need expression templates to make C++ code using MS’s compiler technology compete with a good FORTRAN compiler (I’m old-fashioned, FORTRAN is the FORmula TRANslator and therefore properly written in CAPS), then that’s not “absolutely brilliant”, it’s an absolutely messed-up compiler (or given C and C++ semantics, an unfortunate consequence of the language).”

    dhogaza, the “absolutely brilliant” thing about using the expression template idiom to implement matrix and vector classes is that you can write C++ code like this:

    v = M*x + b;

    and have the compiler turn it into code like this:

    v[0] = M[0][0]*x[0] + M[0][1]*x[1] + … + b[0];
    v[1] = M[1][0]*x[0] + M[1][1]*x[1] + … + b[1];

    (and some compilers can, in turn, automatically vectorise those statements)

    IOW, you get the performance of hand-crafted statements while still being able to use a nice syntax, and this holds for arbitrarily complex expressions. A naive implementation of those same classes would introduce one temporary vector to hold the result of M*x, a second temporary vector to hold the result of adding the first temporary vector to b, and then finally copy the second temporary vector into v (although the final copy should be elided by a good compiler using Return Value Optimisation).

    The reason this is not a “compiler” thing in the case of C++ is that matrix and vector classes are not included in the language and so must be implemented within the language. The reason they are not included in the language is that C++ is intended to operate in a wide range of domains and there is no one-size-fits-all implementation that suits everybody. Besides, the language is powerful enough that the programmer can implement them within the language and still get the performance they could expect from a “native” implementation if they do it right.

    Note that this is not a limitation of “MS’s compiler technology”.

    “Claiming that a language is superior because “absolutely brilliant tricks can make it be as efficiently compiled as straightforward programming techniques in another language” is … not even weak.”

    I agree, that would be a strange reason to claim a language is superior. Who said that? I was advocating Fortran (NB: http://en.wikipedia.org/wiki/Fortran#cite_note-0) precisely because “all sorts of advanced tricks” would be required to compete with Fortran on its home turf and I didn’t think climate scientists should be investing the effort required to attain that degree of proficiency.

    I wrote: “And that’s the point. Most scientists aren’t professional programmers. To be really good at the craft generally requires a relevant degree (not absolutely required, but very useful for the background theory) and quite a lot of experience. These scientists simply need some mathematical model implemented, and for many of them, Fortran is a language that allows them to do that with little effort.”

    649, dhogaza:

    “And why would someone suggest using a language that you apparently believe would require more effort?”

    Since I clearly wasn’t advocating C++ in this particular case, I presume you mean for normal software development? In that case, simply because once you are proficient, it requires less effort. As a perfect example, the second code snippet above is valid C code; it requires less effort to learn C than C++, and if you learn C then you could happily write code like that all day long. To write the necessary classes in C++ that would allow you to write expressions like the first snippet that will execute as efficiently as the second takes much more work and expertise, but once you have done that, it is clearly easier to write expressions like the first one (and easier to verify their correctness on visual inspection, because they look like the original mathematical formulae) than it is to write expressions like the second one.

    So if you are going to be writing and supporting large scale software products then the investment in mastering a language like C++ can pay off in the long run. But if you’re just putting together little test programs as a sideline to your main task then you’re unlikely to write enough code to pay back the effort required to master the language.

    “Hint: the whole point of programming language design is to reduce effort.”

    Precisely. But it’s not just reducing effort in learning the language, it’s reducing the effort overall. A language might take more effort to learn but if that makes constructing solutions easier then the total effort can be less if you spend enough time constructing solutions. (Ironically, one of the things that makes C++ more complex to learn is that it is a multi-paradigm language. The reason it is multi-paradigm is because sometimes it takes less effort to solve something one way rather than another.)

    Think of it like learning to ride a bicycle or drive a car. If you don’t need to move around much, then not bothering to learn and instead just walking everywhere is a win. But at a certain point, the effort invested in learning pays off in the reduction in effort required to travel. Of course, for short trips (like collecting the mail from the mailbox), walking is still the better option; likewise, for simple, one-off programs, Python (for example) may be a better choice than C++.

    “I’d agree with you if you understand the design goals of C++ to be different … but, then again, Strastroup knew (and knows) nothing of language design …”

    I disagree very strongly with that, but I don’t think this is the time or place to embark on a pointless language war, especially since I was using the point that I normally advocate C++ to lend weight to my observation that in this case I think Fortran is the right option for the reasons I gave. You did realise that, right?

  5. 655

    #651 Tilo Reber

    Ah the famous global ice extent graph that shows nothing has changed… unless of course you look closely and put it in context.

    First the graph shows an extent decline. Denialists love the graph though because at first glance it looks like nothing has changed.

    However, as I already pointed out and you apparently did not pay attention to, the ice extent in the Antarctic has increased as expected with global warming and the Arctic has decreased, so in fact the wonderful graph you are showing us confirms the GCM’s are doing their job and global warming is human caused. Thanks for showing that to everyone.

    As I said, and you apparently did not pay attention to what I said (#633), ice volume in the Arctic is telling the story…

    Try to pay attention Tilo, you would not want the nice people here to think you are ignorant, as in ignoring the context and information, would you?

  6. 656
    Completely Fed Up says:

    “It shows very low levels of sea ice for most of 2007 and some degree of recovery since.”

    And why did Tilo pick 2007?

    Because it was a catastrophic year for ice retreat.

    And why is he concentrating on ice extent rather than ice volume? We have the technology to measure it now. It’s because he wants to lie about what’s happening but cannot outright lie.

    So he picks and chooses what to say.

    There’s a reason why we swear to tell “the whole truth” in court…

  7. 657
    Completely Fed Up says:

    John P: “Media such as E&E have rather obvious bias. ”

    Is that the one where they have explicitly stated their bias?

  8. 658
    Completely Fed Up says:

    Tilo revels in his ignorance, reifying it:

    “There would have to be a lot of change at the poles at a time when the rest of the planet isn’t changing at all. Why should polar temperature be changing drastically at a time when the rest of the planet isn’t changing at all. That doesn’t make sense to me.”

    Yup, one of the fingerprints of AGW is that the poles heat more than the equator.

    And please show that the rest of the planet isn’t changing.

    But the proudest statement is the last one.

    Why must your inability to understand prove your thesis?

  9. 659
    Completely Fed Up says:

    Tilo also assumes he knows all: “Supposedly not as cold. So it shouldn’t grow back as far. ”

    Shouldn’t? Done the maths?

    Or did you pull that from the nether regions, Tilo? And polish it up to present as conclusive because you like the look of it?

    It shouldn’t grow back AS THICK.

    And guess what? We can see that. Sea ice isn’t growing back as thick.

    Mind you, he still doesn’t get the measurement of sea ice extent isn’t “solid ice” but “how far out is there still quite a bit of ice”, therefore the extent can be far more affected by breakup of ice drifting away (which breakup is easier if you have thinner ice) than by how cold it is.

  10. 660
    Steve Bloom says:

    Tilo, it’s amusing to see you trying to argue about Arctic sea ice from first principles, but it turns out there are, you know, actual observations that contradict your hopes. See here. But it’s even worse than that, it turns out. See here.

    Also, as you can also see from the first link, the thick ice is never centered on the pole (due to prevailing currents in the Arctic Ocean). Note that recently the area of thick ice hasn’t even included the pole.

    I found all of this in less than a minute with teh google. Why not you, next time?

    Oh, and regarding your argument from personal incredulity about polar amplification, see this new paper. Figure 5 in particular is illuminating. Note that the paper regards a planet nearly identical to the one we live on, although with a slightly lower CO2 level (and sufficient time for the climate to have come into equilibrium with it).

  11. 661
    Ray Ladbury says:

    Tilo Reber says of ice growing back in the cold winter:
    “Supposedly not as cold. So it shouldn’t grow back as far. Using your previous example, once the melt has happened, it shouldn’t freeze back. At least not as far out.”

    Tilo, now you are just making sh*t up! Dude, have you ever watched ice freeze on a pond or stream? Once you have even a thin skin of ice, you have no more evaporation (remember, you are about at the triple point) and much less heat exchange. If it is sufficiently cold it will freeze. The question is whether it will melt in the summer so that you don’t get thick multi-year ice forming. Tilo, you can look this stuff up rather than making it up.

    Given your rather tenuous understanding of the physics, it is not surprising that you are confused. My solution to that would be to try and learn the physics rather than rejecting all the science, but, hey, maybe that’s just me.

  12. 662
    Ray Ladbury says:

    Tilo, your own graph shows that we’ve lost between 2-3 million sq. km of ice at minimum extent and bit over a million at maximum extent! How can you claim that supports your argument?

  13. 663

    Tilo, perhaps you should try replacing the assumption of some linear relationship between latitude and ice thickness with actual data. It’s not hard to find.

    http://www.nasa.gov/images/content/365869main_earth2-20090707-full.jpg
    http://www.nasa.gov/topics/earth/features/icesat-20090707.html

    In fact, the thickest ice is clearly just north of the Canadian archipelago. And you have essentially flat distributions stretching for hundreds of kilometers.

  14. 664

    That line in the C output statement should have read “flux density” rather than “absolute magnitude,” of course. Sorry about that. That’ll teach me to cut and paste code.

  15. 665

    #653 Tilo Reber

    As has been discussed ad infinitum on this site. Weather is not climate and the climate signal is generally understood as 30+ years with attribution in order to identify the signal above the noise

    http://www.nasa.gov/mission_pages/noaa-n/climate/climate_weather.html

    You’re inferring that you trust short term data over long which translates to you trust weather over climate, which translates to you trust the chaos in the noise more that the signal

    Therefore your argument simply does not stand to well reasoned logic.

    What is interesting to note is that you agree with charts such as global ice extent that when in context show that you agree with AGW since it strongly supports the case when understood in context with the models and predictions. This of course makes me wonder why you have a problem with AGW since it looks like you agree with the evidence, including the norther amplification effect.

    Generally, you are a bit confused on the edge v. thickness argument. Edges can even remain relatively the same and still lose thickness in the middle. The really thick stuff in the Arctic is not in the middle (at the north pole, it is more bunched up near Greenland and the Canadian archipelago, and the edges are not stable as you seem to think.

    http://nsidc.org/arcticseaicenews/2009/040609.html

    http://nsidc.org/images/arcticseaicenews/20091207_Figure3.png

  16. 666
    Tilo Reber says:

    Doug: #652
    “Can you show me the “recovery” in this?”

    Go back and see what I said Doug. Then look at your chart. Not the trend line. The data. The trend line carries the past into the present.

    “I’ll stick with November, but you can pick any month you like.”

    I don’t want a month, I want all months. And you might want to account for the fact that the earth has 2 poles like my chart does.

    “Your stage business about thickness versus extent is potentially distracting, but first you have to explain the “recovery” bit.”

    John claimed that ice was thinning at a rate of 10% a year. That would require a lot more area shrinkage than we are seeing. And we are not seeing any since 2007.

    Before you go off on the shortness of the period, remember that I also said this in 628. “But the recent stabilization of the Arctic and Antartic sea ice area makes me think that we may be right on the border of how much melt we are going to get – at least at this temperature. I think we’ll need a few more years to be sure. ”

    And remember that this is said in context of melting all of the Arctic sea ice in the summers without further elevation of temperature. Keep the context.

  17. 667
    Tilo Reber says:

    John: #655
    However, as I already pointed out and you apparently did not pay attention to, the ice extent in the Antarctic has increased as expected with global warming.

    No John, as I previously pointed out, your explanation of the effect of global warming on the Antarctic is false. Your explanation works for explaining the increase in the thickness of the land based ice sheet. It has nothing to do at all with sea based ice extent. Sea based ice doesn’t need more snow or more moisture in the air. The sea has all the raw material necessary to produce ice. Adding more does nothing to increase the ice extent.

    “and the Arctic has decreased”

    Yes, the area decreased until 2007. It recovered after that. As I already said, we need more time to see if that is a stabilization.

  18. 668
    Completely Fed Up says:

    Tilo
    “However, as I already pointed out and you apparently did not pay attention to, the ice extent in the Antarctic has increased as expected with global warming.”

    So you agree that antarctic ice extension is a model consequence of global warming by AGW and therefore constitutes a proof of the validity of those models. Especially since such a change is counter-intuitive.

    “Yes, the area decreased until 2007. It recovered after that.”

    Nope, there is no evidence the ice has recovered.

    Is the extent back to the same levels?

    No.

    Recovered?

    No.

  19. 669
    Completely Fed Up says:

    “I don’t want a month, I want all months.”

    On the scale of climate, there’s no difference between 1 month and 12 consecutive months.

    You want all you like, but wanting insufficient data to make a conclusion doesn’t let you make a conclusion with insufficient data.

  20. 670
    JasonB says:

    653, Tilo Reber:

    “I’m deducing that the rest of the planet isn’t changing at all from this:

    http://4.bp.blogspot.com/__VkzVMn3cHA/SQkAxK2k6CI/AAAAAAAAADs/F4NlhqTzFgM/s1600-h/U+11+Year+Temp+Data.bmp

    It tells me two things. The trend since 1998 has been relatively flat – at least through 2008.”

    Seriously?

    Please, don’t insult my intelligence. I can’t believe you have honestly failed to notice all of the excellent articles around explaining what is wrong with the above statement. Assuming that I’m not aware of them is just rude.

    You may want to consider Pat Michael’s advice: http://www.youtube.com/user/greenman3610#p/u/9/QwnrpwctIh4

    You may also want to think about what happens if you start a year earlier or a year later: http://www.woodfortrees.org/plot/hadcrut3vgl/from:1997/plot/hadcrut3vgl/from:1997/trend/plot/hadcrut3vgl/from:1998/trend/plot/hadcrut3vgl/from:1999/trend

    “This is half of the predicted IPCC decadal warming due to CO2. I consider that significant.”

    Sadly, merely “considering” it significant doesn’t make it so:

    http://tamino.wordpress.com/2009/12/15/how-long/

    You really should look at this as well:

    http://tamino.wordpress.com/2009/12/07/riddle-me-this/

    “But if it’s stronger than the warming across the rest of the globe, what do we get when we multiply zero.”

    Why would anybody be multiplying anything by zero? That doesn’t even begin to make sense.

    “And I agree that it is a good reason. But when other sources diverge, you need to look at the sensibility of the divergence. Saying that it all comes from the small areas at the pole is not sensible to me for the reasons that I gave above.”

    OK, if you want another explanation for why HadCrut underestimates the warming trend, try this:

    http://www.metoffice.gov.uk/corporate/pressoffice/2009/pr20091218b.html

    Since the poles aren’t the only places that HadCrut has no data for, and those “missing” places just happen to also be warming more than average, it’s not surprising that there’s a difference in trend.

    Explain to me again a logical reason for choosing HadCrut over GISS.

  21. 671
    Completely Fed Up says:

    “John claimed that ice was thinning at a rate of 10% a year. That would require a lot more area shrinkage than we are seeing. And we are not seeing any since 2007.”

    Nope, that would not necessarily require ANY area shrinkage.

    Think of a block of processed cheese, 10 slices deep.

    Eat the top one.

    You have now reduced the thickness by 10% yet reduced the coverage not at all.

    And there HAS been shrinkage, you even concede it. So you have to prove that this shrinkage is insufficient.

    Don’t just state it.

    Prove it.

  22. 672

    #657 Completely Fed Up

    Yes.

  23. 673
    Tilo Reber says:

    Completely: #659
    “Mind you, he still doesn’t get the measurement of sea ice extent isn’t “solid ice” but “how far out is there still quite a bit of ice”, therefore the extent can be far more affected by breakup of ice drifting away (which breakup is easier if you have thinner ice) than by how cold it is.”

    Bad logic. First of all, when you drop beyond a certain density of broken up sea ice it’s no longer included in the sea ice area. Second of all, when you have more solid ice towards the center, you still have thinner, broken up ice at the perimeter, and you have a bigger perimeter, so the resulting sea ice area remains larger.

    The argument remains. If the ice is getting significantly thinner (10% per year), then the area should be getting significantly smaller as well.

  24. 674
    Hank Roberts says:

    Sorry, Tilo, you’re wrong in your claim of certainty about how the increased sea ice forms, maximally wrong one might say — you’re making a flat statement as though you had some fact, waving your hands and asserting what you want.

    (What became of monicker anyhow, do you trade off?)

    You know how to look this stuff up. You could do so, but you don’t.

    For any new reader,
    http://scholar.google.com/scholar?hl=en&q=-arctic+%2Bantarctic+%2B%22sea+ice%22+AR4&btnG=Search&as_sdt=2001&as_ylo=2007&as_vis=1

    Likely contributors: more warm ocean currents reaching the Antarctic ice along the seashore; that makes for more fresh water melted off the fixed ice; fresh water floating on top of the salt water freezes faster.

    I’d speculate that one possible approach would be to test the isotope ratios of the seasonal sea ice along the Antarctic edge to see if the water in it came from old water that spent a long time as glacial and fixed ice, then melted, then refroze.

    (Anyone working in the area know if that’s been looked at or if samples are available that could be looked at? Plenty to be looked into)

    For example: http://www.agu.org/journals/gl/gl0722/2007GL031648/

  25. 675

    #666 Tilo Reber

    As to ice extent ‘months’. If you want to see the trend use more that 12 months. weather is not climate Yo say you want all months then what does this chart tell you about ice extent?

    http://nsidc.org/images/arcticseaicenews/20091207_Figure3.png

    The current ice volume loss does not require ice extent loss. Ice extent loss is occurring also though. Ever been ice skating on a lake, the size of the lake does not determine if the ice is thick enough to skate on and the size of the lake does not change, your argument does not stand.

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/365871main_earth3-20090707-full.jpg/view

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/365869main_earth2-20090707-full.jpg/view

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/20090406_Figure5.png/view

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/20090406_animation.gif/view

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/20080924_Figure3.jpg/view

    http://www.ossfoundation.us/projects/environment/global-warming/myths/images/arctic/20080924_Figure3.jpg/view

    Your argument that we need “a few more years to be sure” has no credibility based on the evidence.

  26. 676
    Tilo Reber says:

    Completely:
    “Eat the top one.

    You have now reduced the thickness by 10% yet reduced the coverage not at all.”

    Again, bad logic. The sea ice is not like a block of cheese. Think of it as being more like a discus with a flat top. It’s thick in the middle and thin at the edges. Then when you remove a certain thickness across the whole thing, you also shrink the surface area.

  27. 677
    Doug Bostrom says:

    Tilo Reber says: 5 January 2010 at 11:20 AM

    “Go back and see what I said Doug. Then look at your chart. Not the trend line. The data. The trend line carries the past into the present.”

    Yes, the data forces the trend line to slope downward toward the right. In other words, the data says the ice extent is decreasing. Pick any month you want, all of ‘em, you’ll see the same thing.

    I refuse to believe you’re psychotic.

  28. 678
    Completely Fed Up says:

    “Explain to me again a logical reason for choosing HadCrut over GISS.”

    I can, though it’s not one he’d admit to: it says what he likes to hear.

    This is called cherry picking.

    It’s the same reason he picks 2007 for sea ice extent and even the choosing of sea ice extent as a proxy for temperatures.

    Because not picking them ruins his argument.

  29. 679

    #667 Tilo Reber

    As to Antarctic sea ice extent:

    http://www.skepticalscience.com/Why-is-Antarctic-sea-ice-increasing.html
    http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf

    Your Arctic recovery meme is based on short term natural variability and has less to do with climate that you would like to believe.

    Climate is generally understood to be 30+ years This web site is about climate, and you keep bringing up the weather???

    You need to understand what you are looking at, and apparently you don’t. You need to realize that your lack of understanding does not change the relevant context of the evidence or the scientific understanding. In other words your opinion does not overturn science.

  30. 680
    Steve Bloom says:

    Tilo, teh google would have also quickly led you to things like this regarding the Antarctic sea ice. Interestingly, while there’s been a small expanding trend, it’s been geographically very uneven. I don’t recall seeing you explain or even mention that.

  31. 681
    dhogaza says:

    Completely Fed Up:

    Tilo
    “However, as I already pointed out and you apparently did not pay attention to, the ice extent in the Antarctic has increased as expected with global warming.”

    Actually, you've misattributed the statement, Tilo was quoting John. Tilo then went on to disagree with John.

    So you agree that antarctic ice extension is a model consequence of global warming by AGW and therefore constitutes a proof of the validity of those models. Especially since such a change is counter-intuitive.

    So, no, he doesn’t.

    Anyway, Tilo rejects observational data that doesn’t conform to his world view, such as the fact that arctic sea ice volume has steadily decreased, the fact that we’re at essentially the same record minimum as in 2007 at the moment doesn’t show “recovery from 2007″, etc.

    Tilo’s been spinning the same tired tales for years, now.

  32. 682
    Tilo Reber says:

    Ray: #661
    “If it is sufficiently cold it will freeze.”

    Right. Point being that if we are warming it will not be sufficiently cold as far north as it was when we were colder.

  33. 683
    Bradley McKinley says:

    [Response: You need to be more specific - what time period? - gavin]

    I was just looking at the first graph, and referring to the period 1980-2009. It looked to me like you could still be inside the gray if the observed record started around -0.12 and ended at +0.06, for a total change of only 0.18 over the ~30 year period. That is what I was referring to as a “trivial” amount of warming. I think I see where you are going though, and that is that the model’s forecast curves upwards in the post-2000 period, meaning that you still couldn’t be within the 95% interval with only 0.06 rise per decade for very long. What is the minimum amount of warming you could see through 2100 and still be inside 95% of the model runs? Is it 1.7 for A1B?

    [Response: For the model runs, the 95% lowest bound on trends from 1980-2009 is 0.07 deg C/dec (mean is exactly 0.2 degC/dec) - actual trends were 0.16 deg C/dec. From 2010 to 2100, the range for the A1B scenarios is [0.15,0.38] (mean 0.26) degC/dec (that’s a rise of between 1.7 and 3.6 deg C from now to 2100). – gavin]

  34. 684
    Completely Fed Up says:

    “Point being that if we are warming it will not be sufficiently cold as far north as it was when we were colder.”

    No.

    That isn’t the point.

    It doesn’t even fall out of any sensible thinking on it.

    Sea ice extends where some “pixel” is at least 15% ice. Therefore the sea ice extent is highly dependent on breakup.

    And if it is -1C and warms by 1C, it’s gotten warmer but hasn’t gotten any less frozen.

    Plus, what do you have surrounding the North Pole (as opposed to the South one)?

    Land.

    You’re waving your arms around like Magnus Pike and making as much sense as Snow’s “swingometer”.

  35. 685
    Completely Fed Up says:

    “Again, bad logic. The sea ice is not like a block of cheese. Think of it as being more like a discus with a flat top.”

    Again, bad logic. The sea ice is not like a discus with a flat top. The flat top has already once been brought to your attention but you ignore it (“I see no ships!”). But it;’s more like a slush puppy poured out in to a large bowl.

    Sea ice extends to where there is about 5x more “not ice” than ice.

    So how can sea ice extent be an absolute reading of sea ice extend without seawater?

  36. 686
    Completely Fed Up says:

    For all those complaining about the short shrift some dumb questions get, link to Tilo’s posts and his refusal to read anything he doesn’t like.

  37. 687
    Tilo Reber says:

    Kevin: #663
    “Tilo, perhaps you should try replacing the assumption of some linear relationship between latitude and ice thickness with actual data. It’s not hard to find.”

    Kevin, my argument doesn’t depend on a linear relationship. And it doesn’t depend on the thickest ice being at exactly the north pole. Do you get a lot of ice at the poles and is it cold at the poles? Yes. Do your get a lot of ice at the equator and is it cold at the equator? No. In general, does ice get thinner as you get away from the poles? Yes.

    It doesn’t matter if the shape is not perfect or if the center of the thickest ice isn’t exactly at the pole. The idea that thinner ice should mean less ice area still applies.

  38. 688

    #676 Tilo Reber

    Well, there certainly is a thickness problem here ;)

    Tilo, try thinking of it this way. You have a block of ice, you carve off half of it from the bottom, does the surface area change? No. It’s a simple illustration. the real world is more dynamic but your logic is completely screwed up on this.

    Now run along and tell your friends how mean I am that I was so abusive as to insult your logic.

  39. 689
    Completely Fed Up says:

    Tilo: “And it doesn’t depend on the thickest ice being at exactly the north pole.”

    Really? May I remind you:

    “Think of it as being more like a discus with a flat top.”

  40. 690

    #686 Tilo Reber

    I admit that in your view, you are correct. Unfortunately your view is not in line with the world of evidence and observation called reality.

    To paraphrase Newton, ‘if you have seen so little, it is because you remain stooped to limit your view’.

  41. 691
    dhogaza says:

    Among other things, Tilo’s ignoring the effects of currents and wind …

    Tilo, there’s not sea ice at the equator, but you can find penguins off the west coast of Ecuador and the water there is much colder than the more northern Pacific coast of Costa Rica (I’ve swum in both). Why do you think that is?

  42. 692

    Tilo: I consider that significant.

    BPL: Forgive me if this sounds hostile, but nobody cares what YOU consider significant. In science, “significant” refers to the statistical significance of a measurement, and is something that can be objectively measured. Google “significance testing,” or better yet, take a first-year statistics course.

  43. 693
    Ray Ladbury says:

    Tilo, Global warming does not mean it won’t be below freezing in December north of 50 deg. N. Good lord, I knew I should have bought up some straw. All the straw men you are constructing there won’t be any left.

    Dude, what is happening in the North is 1)Ice is melting in the summer further North than at any time in recorded history. 2)The ocean refreezes in the Winter. 3)It melts in the Summer again.

    It takes several years to build up thick ice. A yearly freeze-thaw cycle precludes thickening. Go learn some science. PLEASE!

  44. 694
    Tilo Reber says:

    JasonB: #670
    “You may want to consider Pat Michael’s advice:”

    Jason, it’s almost as though you haven’t paid attention to anything that we have talked about. Take Michaels objection to starting with an El Nino year and ending with a La Nina year. Why do you think that we have been talking about ENSO corrected data all of this time?

    Take Michaels point about not making the assertion that global warming has stopped. I’ve never made that statement. My statement is that there hasn’t been any since 1998. Those are two completely different things.

    JasonB:
    “You may also want to think about what happens if you start a year earlier or a year later:”

    Same point. That’s why we want to use ENSO corrected data.

    Now, let’s seperate what we are debating about into two different parts. The first concerns what has happened since 1998. The second is if that is significant or not.

    The skeptics statement is that the climate has been essentially flat since 1998. I think that ENSO corrected HadCrut3 and ENSO corrected UAH and ENSO corrected RSS will all show this. If you want to use the outlier, then be my guest. But even your outlier has less warming than predicted by the IPCC.

    Now, regarding the element of significance, I don’t accept Tamino’s arguments. Tamino censors everyone with significant disagreements. I don’t consider any of his posts as being resolved issues since he doesn’t give the opposition a chance to speak. Besides, what happened to your demand for only considering peer reviewed papers as authoritative when it comes to quoting your favorite web site.

    I also find Tamino’s approach as unconvincing because it is not adequately related to physical processes. The idea that you have to filter out elements of natural variability to see a trend is a good one. The problem is when you identify a trend that is shorter than natural cycles of variability. The thirty year rule will not cover all cycles. For example, one side of a PDO cycle can be that long – so you can end up identifying a trend that is nothing more than one phase of a PDO cycle. Apparently, Tamino has now come up with a number that says 15 years is significant. That would be even more subject to identifying a false trend due to natural variability. I think that the better approach is to identify the natural elements of variability and remove them. Then you should be able to identify a trend in a shorter time period. In this case, when we remove the elements that we know about since 1998, we are still flat. This means that if CO2 is forcing at the level that is claimed, then we don’t know enough about the natural elements of variation. Or if we do know enough about it, then the CO2 forcing is not as large as claimed.

    And here is a paper from Science that places a lot of significance on just ten years worth of data.

    http://www.sciencemag.org/cgi/content/abstract/1110252

    From the abstract:
    “This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years.”

    JasonB:
    “Since the poles aren’t the only places that HadCrut has no data for, and those “missing” places just happen to also be warming more than average, it’s not surprising that there’s a difference in trend.”

    The satellites are not missing those other areas, and their trend is slightly lower, even, than HadCrut3.

  45. 695
    Tilo Reber says:

    John: #688

    “Tilo, try thinking of it this way. You have a block of ice, you carve off half of it from the bottom, does the surface area change? No. It’s a simple illustration. the real world is more dynamic but your logic is completely screwed up on this.”

    Been there John. See #676.

  46. 696
    Doug Bostrom says:

    Tilo, I’m still waiting for your explanation of the recovery of Arctic sea ice.

  47. 697
    Tilo Reber says:

    dhogaza: #691

    “Among other things, Tilo’s ignoring the effects of currents and wind …”

    That is true, dhogaza, I am. Can you explain how that plays into the idea that thinning ice should also have shrinking ice area?

    You may all be curious to know that the UAH December anomaly is 0.28C. I know, I know – it’s only weather. I was a little suprised. I thought it would be warmer since the El Nino is still at full strength and since there is a very hot spot in the southern pacific that is the size of the US.

    [Response: Much as the subject appears to fascinate others, we are not interested in a month by month or week by week accounting of the weather. Take it elsewhere. - gavin]

  48. 698
    David B. Benson says:

    Tilo Reber (694) — Tamino’s Open Mind is a “stupid-free” zone for those interested in discovering how statistics is applied to aspects of climatology. I find it most informative; reading there has induced me to start studying

    Jianqing Fan & Qiwei Yao
    Nonlinear Time Series: Nonparametric and parametric methods
    Springer Verlag, 2003.

    At this point I Know have some sort of grip of the linear ARMA models.

    Next, there are very, very few “cycles” in climatological data. There are “oscillations”, meaning just variability and most of this variability is just pink or red-pink noise:
    http://en.wikipedia.org/wiki/Pink_noise
    TO some extent there are quasi-periodic oscillations (QPO) such as the quasi-biannual oscillation (QBO); such can be modeled by ARMA processes but not by old-fashioned periodic functions.

    You should check, but it is highly likely the satellities are missing both polar regions. In addition, I believe you are incorrecvt about RSS.

  49. 699
    Hank Roberts says:

    > here is a paper from Science that places a lot of
    > significance on just ten years worth of data.

    Tilo won’t respond except with more red herring, but for any youngster reading along, some herring detection here:

    What does “a lot of significance” mean to Tilo?
    What does significance mean to a statistician?
    Why are these different?

    Compare noise versus signal and years to detect a trend:
    – annual global measurements (ONE data point each year)
    – sea temperature measurements (how many data points?)

    See also the citing papers, including
    http://www.pnas.org/content/106/38/16120.abstract

    and http://www.arctic.noaa.gov/reportcard/seaice.html

  50. 700

    #694 Tilo Reber

    Short terms can work if you can identify the attribution and relative forcing amounts. Ocean cycles are good in this respect. Science certainly does not know everything about ocean cycles but that does not mean science knows nothing.

    Have you considered politics, your are quite the spinner of reality, or quite likely you simply don’t know enough about the science to understand the context and relevance of what you are looking at, as you have repeatedly shown in your posts.

    My guess is that you are either paid to obfuscate, or you are doing this of your own accord. I hope it is the former because if it is the latter, then you have more serious problems.


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