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Climate Hustle

Hockey Stick Own Goal

Posted on 23 February 2011 by dana1981

In this post we continue our Prudent Path Week theme, and the examination of the two documents the "skeptics" referenced in their recent letter to Congress — 'Carbon Dioxide and Earth's Future: Pursuing the Prudent Path' and the NIPCC report.  Specifically, we examine a major contradiction between the two reports regarding a key factor in climate science - climate sensitivity.

Medieval vs. Current Global Temperature

In their Prudent Path document, Craig and Sherwood Idso argue that the Medieval Warm Period (MWP) was at least as hot as today.

"it was just as warm as, or even warmer than, it has been recently during both the Roman and Medieval Warm Periods"

Informal Idsos

The document spends several pages qualitatively discussing various temperature proxy data sets from various isolated geographic locations — one of the main pursuits of the Idsos' website co2science.org.  The only response this endeavor warrants is the suggestion that if the Idsos would like to attempt to use this data to demonstrate that the MWP was hotter than today, they should perform a quantitative assessment — combine these proxies into either a northern hemisphere or global data set, estimate the average temperature, and submit their results to a peer-reviewed scientific journal.  Over a dozen such millennial northern hemisphere reconstructions have been peer-reviewed, and all agree that current temperatures are hotter than during the MWP peak.

Ljungqvist (2010)

The document also relies fairly heavily on one such millennial northern hemisphere reconstruction — Ljungqvist (2010) — which the Idsos refer to as a "stellar effort". However, this reconstruction is not substantially different from the many other millennial northern hemisphere temperature reconstructions, as Ljungqvist himself states in his paper:

“Our temperature reconstruction agrees well with the reconstructions by Moberg et al. (2005) and Mann et al. (2008) with regard to the amplitude of the variability as well as the timing of warm and cold periods, except for the period c. AD 300–800, despite significant differences in both data coverage and methodology.”

Contrary to the Idsos' claims in the Prudent Path document, Ljungqvist says the following when combining his proxy reconstruction with recent instrumental temperature data:

“Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period”

Indeed by plotting Ljungqvist's data along with Moberg et al. (2005), Mann et al. (2008), and the surface temperature record, we can confirm that the three reconstructions are very similar, and all show the peak of the MWP approximately 0.5°C cooler than today's temperatures (Figure 1).


Figure 1: Moberg et al. 2005 NH (blue), Mann et al. 2008 EIV NH (red), Ljungqvist  2010 NH (green), and GISS land+ocean NH (black).  Courtesy of Robert Way and John Cook.

Thus we can see that the Prudent Path document's own references do not support its claim that the MWP peak was as hot or hotter than today's temperatures.  This is a good thing, because the larger past natural temperature changes were, the larger the climate sensitivity.

Skeptic Climate Sensitivity Contradiction

A quick perusal through the Skeptical Science rebuttal database makes it clear that "skeptic" arguments often contradict each other.  Perhaps the worst contradiction of them all are the conflicting claims that the MWP was hotter than today, and that climate sensitivity is low.

Skepticism Requires Low Climate Sensitivity

Climate sensitivity (the amount the planet's average surface temperature will warm given a certain energy imbalance, including feedbacks) is the key to global warming skepticism.  The amount of warming at the Earth's surface depends on two factors — the size of the energy imbalance, and the climate sensitivity to that energy.  However, the first factor (the energy imbalance caused by the increase in greenhouse gases) is a well-measured and well-known quantity. 

Therefore, the only way to argue that humans aren’t driving global temperatures now, and temperature change over the next century won’t be potentially catastrophic in a business-as-usual scenario, is if climate sensitivity is low.  "Skeptic" climate scientists like Lindzen, Spencer, and Christy realize this, and it's why their arguments consistently center around the argument "climate sensitivity is low". 

The heat trapped by the increased atmospheric CO2 has to go somewhere, and the only way it's not causing and will not cause significant global warming and climate change in the future is if it's suppressed by cooling effects from negative feedbacks.  If this were the case, climate sensitivity would be low.  And this is indeed a key argument made in the NIPCC report:

"Scientific research suggests the model-derived temperature sensitivity of the earth accepted by the IPCC is too large. Corrected feedbacks in the climate system could reduce climate sensitivity to values that are an order of magnitude smaller."

The NIPCC report is claiming that the IPCC sensitivity range is too high by a factor of 10, but the Idso Prudent Path document, by claiming that the MWP was as hot or hotter than today, is arguing that the IPCC sensitivity range is too low.

Hot MWP Means High Sensitivity

As John Cook has previously discussed, arguing for large swings in natural temperature variation such as a particularly hot MWP is akin to arguing for high climate sensitivity.  Several scientific studies have examined the radiative forcings and temperature changes over the past millennium, such as Hegerl et al 2006, as shown in Figure 2:


Figure 2: Climate sensitivity from palaeoreconstructions going back 750 years, combined with climate sensitivity calculated from instrumental records. The horizontal bars represent the 5 to 95% range, indicating a climate sensitivity range of 1.5 to 6.2°C for a doubling of atmospheric CO2 (Hegerl et al 2006).

When you combine the temperature record over the past millennium with climate forcings, you get a most likely climate sensitivity value close to 3°C, consistent with the IPCC climate sensitivity range of 2°C to 4.5°C.  So if the temperature swings were actually larger than in the reconstructions used by Hegerl and other studies on millennial climate sensitivity, it means the climate sensitivity is actually higher than the IPCC has concluded.

The two documents referenced in the "skeptic" letter to Congress blatantly contradict each other on this issue.  The NIPCC report argues that the climate sensitivity is an order of magnitude lower than the IPCC range, while the Idso Prudent Path document indirectly argues that the sensitivity is higher than the IPCC range.  On the most important issue for climate "skeptics" — climate sensitivity — the two documents cited in the "skeptic" letter to Congress contradict each other by a factor of ten.

The True Prudent Path

Ironically, although the two "skeptic" documents differ on the climate sensitivity parameter by an order of magnitude, both are wrong.  There are many independent lines of evidence behind the IPCC climate sensitivity range, meaning that it's exceptionally unlikely that it's wrong by an order of magnitude, as the NIPCC report claims.  And as discussed above, the evidence does not support the Idso claim that the MWP peak was as hot or hotter than today.

Thus the real "prudent path" involves proceeding under the assumption that the well-supported IPCC likely range of climate sensitivity (2 to 4.5°C with a most likely value of 3°C warming for a doubling of atmospheric CO2) is correct.  In this scenario, we are heading towards extremely dangerous and potentially catastrophic warming and climate change this century in a business-as-usual scenario

Thus the true prudent path involves taking immediate action to significantly reduce human CO2 emissions.  If the "skeptics" want to convince us otherwise, they need to start by getting their story straight.

This post was written by Dana Nuccitelli (dana1981) and has been developed into the Intermediate rebuttal to "Ljungqvist broke the hockey stick"

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Comments 101 to 115 out of 115:

  1. HR @100,

    As shown by muoncounter in their post @40, MBH98 is not shown in Fig. 6-10b in AR4, MBH99 is. We have been over this, MBH98 is discussed in AR4 but only because of the controversy surrounding it.

    Really, you guys have nothing and it is showing.
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  2. Invicta @65, Dana @ 67, from the article:

    "When you combine the temperature record over the past millennium with climate forcings, you get a most likely climate sensitivity value close to 3°C, consistent with the IPCC climate sensitivity range of 2°C to 4.5°C. So if the temperature swings were actually larger than in the reconstructions used by Hegerl and other studies on millennial climate sensitivity, it means the climate sensitivity is actually higher than the IPCC has concluded."

    So, Invicta, the thread is saying that if the MWP were warmer than the reconstructions (and hence 1990's temperatures), that is a bad sign for the future because it indicates a high climate sensitivity. A hotter MWP, and a colder LIA would both indicate forecasts for future temperatures are underestimates.

    It does not argue that current temperatures being actually higher than the MWP is a bad thing for our future. That is in fact bad, but only because current forecasts with the current best estimate of climate sensitivity are grim enough.

    I have to assume that Dana was very tired when he responded to you, for his response contradicts the article.
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  3. Robert Way. The thing I love was how the Hadley Climate Research Unit was the focus of the ludicrous "Climate-gate" beat-up, yet now all the "skeptics" are pointing to HadCRU temperature data as better than anyone else's-apparently because it shows a shallower warming trend than GISS or RSS. Boy the own goals from the Denialists are coming in thick & fast!
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  4. Tom, thanks. Not tired, just doing too many things at once! Yes, I meant that if the original hickey stick were correct and the MWP weren't particularly hot, that would be good news.
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  5. Marcus don't you know? Whichever data set shows the least warming at any given time is the good one!
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  6. "The NIPCC report is claiming that the IPCC sensitivity range is too high by a factor of 10, but the Idso Prudent Path document, by claiming that the MWP was as hot or hotter than today, is arguing that the IPCC sensitivity range is too low. "

    I don't quite understand this argument; I haven't seen any comprehensive reconstruction of net forcing over the past millennia, so it would seem to be a non-sequitur to state that the Idso's are necessarily arguing for a high climate sensitivity in arguing for a warm MWP.

    A MWP comparable in temperature to today is virtually impossible given the slew of millennial temperature reconstructions showing otherwise, and there is little indication of any dramatic changes in TSI or volcanic activity that could lead to such a warm MWP, but I'm not sure the latter proposition contradicts Idso's concurrent argument that CS is low.
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  7. Robert @106,

    "I haven't seen any comprehensive reconstruction of net forcing over the past millennia, so it would seem to be a non-sequitur to state that the Idso's are necessarily arguing for a high climate sensitivity in arguing for a warm MWP."

    Actually Hegerl (2006) looked into this. Estimates of the forcing data (solar, aerosol, GHGs etc.) are shown going back to 1000 AD, see Fig. 2.

    Mann et al. (2009) looked into the possible role of internal climate variability over the last 1500 years.
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  8. 58 Tom Curtis

    "In fact, Hegerl produces the most coherent results, ie, with climate sensitivity of solar and GHG forcings being the same, if solar forcings are half that of the estimates which he used. With solar forcings only 1/4 of that which he used, the sensitivity of GHG and solar forcings will still be very close, within limits of error."

    Sorry Tom but I can't see in Hegerl were he says you need to 1/2 the forcing to get a good match. Are you sure you have this the right way around, not multiply by 2 (to 4)? The Foukal Nature Review that I referenced in #54 says

    "We also considered the case where the forcing by the
    dark and bright magnetic components was modified by adding a lowfrequency component69, amplifying the solar forcing range by 3 to 4 over this time period. In this case (red curve), the model cooling trend is closer to the reconstructed palaeotemperature trend."
    Foukal et al 2006 Nature Review


    And that is what I've been reading in the rest of the literature as well.

    "Although the most straightforward mechanism of the sun–
    climate connection is the direct heating of the earth by solar radiation [total solar irradiance (TSI)], it is unlikely that the entire solar influence on climate can be attributed simply to variations in the TSI (2–4)."
    Yamaguchi et al 2010 PNAS

    And from another review on the solar irradiance changes from MM to present based on multiple sources

    "These estimates for century-scale TSI changes of ~1.3-1.6 Wm-2 correspond to a change in mean global radiative forcing of only 0.16-0.28 Wm-2"

    Gray and many other 2010

    The concensus seems to be changes in luminosity/TSI while often synchronous with temperature change are too small to suggest the direct energy changes are driving climate change. I don't know how Hegerl found that the magnitude of TSI changes were too high as you suggest.

    Anyway to bring this back to climate sensitivity. All these papers seem to agree there is no known mechanism by which solar can affect climate change on the scale we are looking at here. It does beg the question how you would calculate climate sensitivity on that basis.
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  9. HR @108, in Hegerl 2007 on table 2, he lists "... the best-guess scaling factor
    for the model’s fingerprint", ie, the factor by which either forcing or sensitivity must be multiplied by to best reproduce the reconstruction. For his reconstruction, for solar forcings, that factor is 0.5, which means, on the basis of that reconstruction, either climate sensitivity to solar forcings are half those of CO2 and aerosols, or that the solar forcings are around half of those reconstructed at the time of his paper. As it happens, new evidence favours the later conclusion. Hence your previously stated concern that the new evidence on solar forcings might require climate scientists to adopt unphyscical climate sensitivities to explain the past is unwarranted.

    Hegerl used the forcing reconstuctions from Crowley 2000, which yields a difference between maximum and minimum net solar forcing of 0.6 w/m^2. Halving that sits very comfortably with Gray et al 2010.

    Having said that, my initial caveat still stands. Neither techiques for reconstructing past forcings or past temperatures are sufficiently exact to tightly constrain climate sensitivity - hence the large error bars in calculatons of sensitivity from data over the last millenium:



    This is one reason to prefer sensitivity calculations based on the last glacial maximum, where the much larger changes in forcings and temperatures restrict the potential error.
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  10. Wow, I completely missed that section just below regarding hot MWP and high climate sensitivity. My apologies...
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  11. Tom Curtis @102 Thanks for the extra enlightenment I was surprised by dana's reply but glad to see he is human
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  12. Yes, definitely human. Last time I checked, anyway.
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  13. Tom Curtis

    OK thanks I hadn't gone back so far in the literature to estimates that were as high as Crowley's and I was working on the basis of the other Hegerl paper where the references were for Lean solar forcings (around 3). That seems to fit with the papers I'd been reading.

    You wrote

    "Hence your previously stated concern that the new evidence on solar forcings might require climate scientists to adopt unphyscical climate sensitivities to explain the past is unwarranted."

    But you've now done the opposite to what Dana did in the post. You've allowed for the changing understanding of solar forcing but have kept Hegerl's temperature reconstructions.

    I'll have a stab at back of the envelope calculations.

    Gray's estimates of changes in solar forcing on centennial/millenial time scales 0.16-0.28 Wm-2

    Natural temperature variability from Fig1 (MWP to MM). I'll be generous at 0.4oC (but I think Ljundquist is maybe 0.6-0.8).

    Lowest Climate sensitivity based on these numbers = (0.4/0.28)*3.7= 5.3
    Highest Climate sensitivity based on these numbers =(0.4/0.16)*3.7= 9.25

    (I have no idea if that's how you do the calculation, I'm wearing my flak jacket)

    Both these numbers are outside the IPCC best guess at climate sensitivity and as I said I think I'm being generous with the temperature variability. The numbers can get even worse. The STEINHILBER reference in #54 has MM to present solar forcing of <0.1. MWP to MM is probably the same (the data and readme file if you want to play with them). Those numbers go beyond problematic and start to get unphysical.

    I think you only keep the IPCC favoured range within the error bars if you retain the lower deltaT reconstructions (early Mann and others) or higher deltaTSI estimates (Lean). If you do that you get wider error bars, I think the IPCC has been working to reduce them. However you approach this it's problematic for the concensus view.

    "Neither techiques for reconstructing past forcings or past temperatures are sufficiently exact to tightly constrain climate sensitivity"

    Look I take your caveat on board. But the science is supposed to have evolved, it's meant to be better now than it was in 1998-2000. If you're making this arguement now in 2011 what should we (or the IPCC) have been saying in 2007 or 2003? It's the IPCC that's suggesting this type of data is supporting evidence for AGW. So is it or isn't it?

    (An unrelated question I have from reading the literature. TSI changes correlate well with temp change over this period. But the magnitude of TSI is too small to account for the change. Doesn't this open up the possibility that there's a big hole in our understanding of solar-climate interactions? I know there are controversial ideas about other solar mechanism for changeing the climate and it's probably not right to discuss those on this thread. But isn't all this demanding higher solar forcing and that coming from somewhere other than direct changes in solar energy output?)
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  14. "TSI changes correlate well with temp change over this period. But the magnitude of TSI is too small to account for the change."

    That would be what feedback is all about. Any change in T affects water vapour for starters, magnifying the forcing whatever its source.
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  15. (Sorry, my line went down as I was submitting my comment @115. Here is the full version.)

    HR @113:

    First, there is nothing wrong with allowing the change in forcings but keeping Husserl's reconstruction. The reconstruction was made independently of estimates of forcings, and based on long series proxies.

    Second, your back of the envelope calculations ignores the other forcings. Of these, the most important in the MWP is the volcanic forcing, which was three times stronger than solar forcing during that period. Based on laying a ruler against Fig 5 a (after blowing it up 750%), the respective forcings are approximately: Volcanic 0.5 w/m^2; solar 0.2 w/m^2; GHG + Aerosol -0.1 w/m^2. (Note, I have used the temperature scale the other forcings against the reported solar forcing.)

    Plugging those figures into the back of envelope calculations we get a climate sensitivity approx = (0.7/0.6)*3.7 = 4.3

    If we then scale back the solar contribution based on Gray's estimates, the net mean MWP forcing is between and 0.45 and 0.5 w/m^2, for a forcing response of between 5.2 and 5.8

    Note that these are probably significant over estimates on the data as I have used the average of Lundqvist's total variation (as given by you) instead of calculating a specific MWP variation. Using the probably more reasonable figure for just the MWP of 0.4 reduces the range to from 3 to 3.3 - hardly a problem for the IPCC. These values are so loosely calculated as to be effectively worthless - I would not trust them to do more than indicate the order of magnitude of the expected effect. But they do show that you cannot simply ignore the non-solar forcings.

    Even if you do, your calculated values are not out of the IPCC ball park as calculated using temperature and forcing reconstructions of the last century. According to AR4, the sensitivity has a probability of around 66% of falling between 1.5 and 6.5 (from eyeballing the chart above) on that data, and a 99% probability of falling between 1 and 9.

    So, once again I conclude that you have not shown there to be any problem with climate sensitivities given the limitations of the data.

    Finally, it is not clear that there is a distinct correlation between temperatures and TSI. Notoriously, such a link has been hard to pin down in the 20th century with regard to the sunspot cycle. Of four reconstructions examined by Husserl 2007, only 1 shows a detectable solar signal, and two show very slight negative correlations with TSI once other forcings have been removed from the signal (or at least require negative scaling factors).

    The apparent correlation seems to be based in part on periods of intense volcanic activity coinciding with certain solar minimuma, along with a feedback based on increased solubility of CO2 in the oceans with declining temperatures.

    There may be a connection between low solar activity and lack of major volcanoes, presumably based on the interactions of the Sun and Earth's magnetic fields modifying the length of the day. There may also be an impact of galactic cosmic rays, not on cloud extent (which as been effectively falsified) but on cloud albedo. But these connections are tenuous and, on current evidence, speculative. These may be fruitful avenues of research but because the connections are so unclear on current data, it is highly unlikely that the end result of such research will make major changes to the current (IPCC) understanding of what drives climate. This is especially true as, in anything, current estimates of TSI are to low to fully explain even that weak effect of solar variation that is detectable.
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  16. scaddenp @114, HR is allowing for feedbacks in his comment; hence his attempt to caclulate rough climate sensitivities.
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  17. Tom,

    "may be a connection between low solar activity and lack of major volcanoes, ... may also be an impact of galactic cosmic rays, ... on cloud albedo."

    They're way off topic, but those are new ones on me. If you can find an appropriate thread, care to explain?
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  18. muoncounter @117, response here.
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  19. HR - sorry, I missed the sensitivity calculation, skimming to fast. One other thing though - you shouldnt be just looking at NH temperatures with a global forcing. SH picture is a little different.
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  20. Figure 1: Moberg et al. 2005 NH (blue), Mann et al. 2008 EIV NH (red), Ljungqvist 2010 NH (green), and GISS land+ocean NH (black). Courtesy of Robert Way and John Cook.

    This is a fascinating graphn thanks Dana. Firstly the reconstructions do follow measured temperatures since ~1900s until 1990 ish which is reassuring to a degree, after which things get hot quickly, 0.2C a decade from 1980, or ~0.6C on 30 years.

    Looking at the graph two things get my interest, there appears to be a ~1000year natural temperature variation of about 0.3C (0.3C either side of the mean) arround a mean of -0.1C (from 0yr to 1980ish) with an added variation of ~+/-0.2C arround the running mean, meaning that (0.3C + 0.2C) or 0.5C above -0.1C would be a thousand year extreme warm year, so that is +0.4C on this chart and there are 2 spikes in blue of that magnitude in the middle of Medeival NH warming event.

    However the mid 1000-2000 cold dip period is cooler than the previous one between 0-1000 years by about 0.1-0.2C suggesting a possible cooling between the two, which is also in keeping with the 2000year cooling trend found in the arctic temperature record and in keeping with orbital variations in the NH which leading a general cooling of the NH at the present time, although this is a very slow cooling.

    All things being equal therefore by natural variation the NH should have been warming from 1500-1600 on wards and 1900-2000 should be the peak of the warming. Without the cooling trend it would be expected from the natural variation that the NH would reach another 1000year peak hot round about now, however this peak should be +0.2C mean with a year to year possibility of +0.2C or +0.4C just like in the 900-1100's and although for an individual year may even surpass this, the probability is less 1:1000 or more.

    Lets not forget the long term cooling due to orbital changes in the NH (clearly the arctic would amplify this effect as orbital effects are greatest nearer the poles), which should be bringing the mean down to lower than -0.1C (i suspect it is -0.1C as the mean for the whole series is skewed to 0C by the inclusion of the recent hot years), which means to get any year hotter than 0.4C than 2000year mean would be a truly exceptional event via natural variation.

    Lastly it looks like the mean has suddenly jumped, (would expect to phase jumps in a choatic system) and the new mean seems be a lot higher as there have just been a 10year period were then mean is 0.8C higher (than -0.1C). It is also of note that 2010 from solar and Nino (mod El Nino 5 months, Strong La Nina 7 months) activity should have been a cooler year than average, yet it was the hottest yet and November 2010 was in a well established La Nina and histroical low of sun activity and yet was also the hottest yet.

    So if 2010 and its weather was a cold year, what is a warm year going to be like?

    Could the mean have shifted again in 2010 with the earth being tipped into a hotter regime like it probably was 1998?

    Would this be in keeping with a step changing choatic system and that would mean that the jumps should get more frequent if the warming influence is maintained?

    As for Climate sensitivity, in the pliocene it 3-5C hotter despite all the natural variation of millions of years, and thus the only substantially different variable was the pCO2 at 350-400ppm although 350ppm more robust from recent evidence. 3-5C would take ~1000years to effectuate due to lags in the system however 60% is realised in the first 100year or so, that means we can expect at least 1.8C to a maximum rise of 3C by 2100, if CO2 levels fall to 350ppm ish.

    The Earth is a choatic system and therefore will have multiply possible CS as parameters change, the amount of ice will make a difference, the orientation of the continents (pliocene was similiar to now), and therefore CS will vary and have high and low possibilities. From the above long term CS for doubling can be high (3-4x pliocene temperature range) and as at present the earth has a pole whose albedo turn arround is very high going from ice to sea which makes sense as a CS amplifyer especially if permafrost GHG gas release is also considered.

    Also all the changes being observed in the system are occuring faster than expected by a CS or only 3C.

    Anyway it is very likely CO2 will hit 450-500ish the way things are going and that is well too high for serious consideration of there being any widespread fruitful scenarios for the future.

    An interesting graph clearly shows the globe is warming and very quickly, however at least natural variation should trend temperatures down a little, unless of course the natural variation seen in the graph is actually mainly a sea-saw NH / SH event due to long term flow patterns in the AMOC as that makes the current global warming even more impressive and is it likely that flucation could be changed or interupted if an external heating influence is added in.
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  21. ranyl,

    Welcome to SkS. You've put a lot into one post; its usually better for everyone (and easier to follow) if you stay topic-specific and break a long post into several smaller ones. Use the Search function to browse the existing threads, which are organized by skeptic 'argument' and comment on the appropriate thread.

    One thing jumps out in a quick scan of your post: "So if 2010 and its weather was a cold year, what is a warm year going to be like?"

    Most put 2010 as tied for the warmest year on record.
    For 2010, the combined global land and ocean surface temperature tied with 2005 as the warmest such period on record, at 0.62°C (1.12°F) above the 20th century average of 13.9°C (57.0°F).

    What a warm year was like can be found in threads such as Extreme weather. Not a pretty picture.

    There's a lot to learn here, because so many posters follow the practice of substantiating their points with references to scientific research. And avoid such declarative statements like 'everybody knows it's warming because ... '.
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  22. Protestant - I can't say that I came around to your point of view. But I do find the divergence from Proxies problem to be too quickly 'splained away and never discussed again.

    I can say your posts made me think about my position, and I appreciate that.

    I thought the moderators were too hard on you, but to their credit, they also kept a tight reign on the pro-AGW posters.

    Thanks for posting, and sticking to your guns.

    I do think it is intellectually unfair to say "a large MWP spike COULD be the influence of internal variability" - and then offer up no coherent theory. It really, truly begs the question: What DID do the warming?

    One avenue your posts directed my brain to was the problem of confirmation bias. I have looked at the evidence and concluded climate science explains the climate (with a few caveats - but on a macro scale the science seems robust). And given that AGW is the name for the climate science explanation of our current situation - I am a "pro-AGW" person. And when new evidence comes in, I apply more scrutiny if it seems to contradict AGW, and less if it seems to confirm it.

    When I begin to think I have a problem here - as your posts did - I fall back to this. Where is the competing theory that explains all the data and evidence, and does not appeal unduly to unknown phenomena? That is where most of the objections to AGW die down.

    And finally, in regard to your claim that un-fiddled data shows .5C, rather than .8C warming. I could accept that at face value and still be very, very worried. Rolling that forward - that would mean a sea level rise in this century of 1-2 meters, instead of 2-4. That would mean 2.5C warming instead of 4C. We are seeing HUGE effects at .5 or .8 and the multi-decadal trend is getting worse. And we are 40 years of warming into your 60 year cycle. When/where and how soon is that cooling coming? Because logic tells us when the sun "wakes up" and we switch from La Nina to El Nino - the experienced warming is going to get worse, not better.
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  23. Muon @ 121. It's true that 2010 is tied has hottest year ever recorded, yet it had a culmination of negative natural forcings (at least 1 major volcanic eruption, below average sun-spot number & a La Nina event) that should have made it *colder* than 2008. So, on that basis, is it fair to say that man-made forcings are now great enough to entirely swamp all natural forcings? Sorry if this is OT, but I'd be interested in your thoughts on this!
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  24. Marcus,

    "at least 1 major volcanic eruption"

    If you're referring to Iceland's Eyjafjallajökull volcano, my understanding was that it wasn't a major climate-mover. Lots of dust, but not enough oomph (it was VEI 4, compared to Pinatubo's VEI 6 -- a logarithmic scale) to put it into the stratosphere.

    "is it fair to say that man-made forcings are now great enough to entirely swamp all natural forcings?"

    I think that is more than fair; a result elegantly shown by Tamino's analysis removing short term factors to find the core trend.

    .

    Tamino also shows separate graphs for volcanic, solar and MEI fluctuations removed from the temperature signal. And the forcing that is left driving the uptrend is ... you guessed it!
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  25. Muoncounter @124:

    Marcus: "is it fair to say that man-made forcings are now great enough to entirely swamp all natural forcings?"

    Muoncounter: "I think that is more than fair ..."

    To put it into context, the trend in temperatures since 1980 is approx 0.12 degrees C per decade (0.116 where underline indicates a recurring integer). For comparison, the average standard deviation of the running 30 year interval over the instrumental period to 1979 is 0.103, so temperature increase per annum is just over a tenth of the normal annual fluctuation in global mean temperatures.

    The fluctuation in regional mean temperatures is, of course, much larger so that at a regional level, annual variation is far more significant.
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  26. "the trend in temperatures since 1980 is approx 0.12 degrees C per decade"

    Tamino's graph shows a slightly higher trend, as do the composite surface reconstructions put together by Ned back in July 2010.



    Northern hemisphere 30 year trends are 2-3 times these rates.

    "average standard deviation of the running 30 year interval over the instrumental period to 1979 is 0.103"

    Do you mean the satellite record since 1979? Or the surface record up to 1979; if so why stop in 1979? In either case, its a noisy signal; hence the rationale (as I read it) for Tamino's filtering process rather than a purely statistical trend removal.
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  27. I won't argue the trends. I simply took the difference between the running 30 year mean terminating in 1981 and in 2010 and divided by three to get a decadal trend. Very rough, but indicative. The 0.15 to 0.17 global trends in your graph only reinforce the point.

    The running 30 year interval is of the combined surface record from this site, and has a terminal year of 1979. The reason for that is that the SD rises rapidly to as high as 0.19 after 1979 because of the rapid rise in temperatures. The average taken over the whole surface record of the running 30 year intervals is 0.115, while the SD of the entire surface record is 0.135
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  28. 115 Tom Curtis

    Tom when you write MWP do you mean MM (Maunder Minimum)? The volcanic forcings in fig5a don't go back as far as the MWP. I've pasted the volcanic forcings from Hegerl 2006 Fig2 (1000AD to 2000AD) into the corner of Dana'a Fig 1. The idea isn't to show the absolute magnitudes but to show how the periods of peak volcanic activity match to the temperature record.



    The problem I have with the importance of volcanic forcing is that it's very short lived. I see the MM coincides with a period of high volcanic activity but it doesn't really explain how we got to the MM. What I mean is the MWP to MM period is 600-700 years of declining temperatures. This period has periods of both high and low volcanic activity. I'm not sure of the resolution in the temperature reconstructions but volcanic may explain some large negative departure in some of the data points (maybe for example those very low spikes at the MM) but they can't really account for the multi-centennial trends. In regard to your mathes wouldn't you have to take some sort of mean volcanic forcing over the full MWP-MM period?

    The only real forcing likely to explain those longer trends are solar except as I keep saying it appears that TSI changes are far too small to explain them.

    "First, there is nothing wrong with allowing the change in forcings but keeping Hegerl's reconstruction."

    I think we both agree that both fields (paleotemperature reconstruction and TSI reconstructions) are fields of science that are in flux, if not still in their infancy then going through a painful adolesence. My contention is the newer paleotemp estimates should be matched with the newer TSI estimates but I concede there is no absolute logic to that. But retain all the estimates and you end up with a spread of climate sensitivity that is so wide to be almost meaningless.

    As you say the IPCC may not exclude climate sensitvity being between 5-9 but just based on the image in #109 then other parts of the science are going to struggle. It looks like models won't handle those well or the LGM. That was my earlier point I think this is not just a problem for skeptics.
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  29. 119 scaddenp

    "One other thing though - you shouldnt be just looking at NH temperatures with a global forcing. "

    I won't argue with you. All the reconstructions are essentially NH even those that purport to be global. Hegerl's work was based on NH reconstructions. So it's not just my problem it's the whole scientific field. I suggest you write to teh IPCC with your concerns.
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  30. HR - in my reading of the paper, they estimate global forcings, run a GLOBAL model, and then extract from that model the temperature series for NH. They are not trying a simple-minded application of sensitivity no.s Remember that sensitivity is an OUTPUT of a model, not an input.
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  31. HR @128, I do mean the Medieval Warm Period. During the Medieval Warm Period, there was an exceptionally low number of volcanoes, particularly at the beginning. Because of the reduced aerosol load that follows, there is significant warming (at least in Husserl's models). A similar, though not as extensive, lack of vulcanism occurred in the early twentieth century, and may partly explain the very warm temperatures in the 1930s and 40s.

    Volcanoes are short lived, but their aerosols can remain aloft in significant quantities for several years. As a result, if several volcanoes occur in a decade, it can significantly lower temperatures for that decade. Given that a single large voclanoe can depress temperatures by up to 0.5 degrees for three years or more, even one large event can drag down the average.

    In that context, consider the sulfate load in a greenland ice core during the Dalton Minimum:



    As you can see, there were two very large volcanoes in that periods, and a continuous sulfate load in the atmosphere. The 1815 volcano (Tambora) is estimated to have generated 14 w/m^2 forcing. Assuming scaling is linear, the background sulfate level would have generated a forcing around -0.5 to -1 w/m^2, or enough for around a 0.5 degree equilibrium decrease in global temperatures after feedbacks. Half a century without volcanoes would remove that negative forcing, and could result (accordingly) in an increase in global meant temperature of up to 0.5 degrees, ie, the equivalent of the MWP.
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  32. Dana in your post, "Contrary to the Idsos' claims in the Prudent Path document, Ljungqvist says the following when combining his proxy reconstruction with recent instrumental temperature data:

    Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades the last two millennia, even the peak of the Medieval Warm Period."

    However, the actual statement by Ljungqvist (2010) (my emphasis added) appears to contradict your contention:

    "Substantial parts of the Roman Warm Period, from the first to the third centuries, and the Medieval Warm Period, from the ninth to the thirteenth centuries, seem to have equalled or exceeded the AD 1961-1990 mean temperature level in the extra-tropical Northern Hemisphere. Since AD 1990, though, average temperatures in the extra-tropical Northern Hemisphere exceed those of any other warm decades [of] the last two millennia, even the peak of the Medieval Warm Period, if we look at the instrumental temperature data spliced to the proxy reconstruction. However, this sharp rise in temperature compared to the magnitude of warmth in previous warm periods should be cautiously interpreted since it is not visible in the proxy reconstruction itself."


    The crux of Ljungqvist's statement which you have minimised, is that the, "instrumental data spliced to the proxy reconstruction" should be cautiously interpreted because the recent proxy data does not emulate the recent instrumental data. In a nutshell this is the "divergence problem."

    Re your comment that, "Indeed by plotting data along with Moberg et al. (2005), Mann et al. (2008), and the surface temperature record, we can confirm that the three reconstructions are very similar, and all show the peak of the MWP approximately 0.5°C cooler than today's temperatures (Figure 1)."

    Your statement that the MWP is 0.5 °C cooler than today is incorrect because you are comparing today's instrumental measurements with yesterday's proxies. To compare instrumental temperatures with proxy temperatures is physically and statistically wrong. The correct methodology is to compare today's proxies with previous proxies.

    I enclose Ljungqvist's original reconstruction in Figure A and I have removed the instrumental calibration data in Figure B for clarity.



    Figure A: Ljungqvist's Reconstruction with Instrumental Data that was used for Calibration



    Figure B: Ljungqvist's Reconstruction with Instrumental Data Deleted

    It is evident from Figures A and B that the MWP was at least as warm as the current warming period. Moberg (2005) and Mann (2008) show similar results when proxies are compared with proxies. Therefore, a correct interpretation is that all three reconstructions show that recent temperatures are similar to the MWP.

    From the foregoing, it would appear that the Prudent Path does support its claim that, if you compare proxies with proxies in your three reconstructions, the MWP was as hot as today.
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    Moderator Response: [DB] Recent evidence shows that the current warmth experienced in Europe is unequaled in the last 4,000 years (another post on this topic is also imminent):
  33. angusmac @132, your contention that it is inappropriate to compare the recent instrumental record with past proxy records is incorrect. The simple fact is that we do not have a broad range of proxy records with global coverage extending to the very recent past, with most proxy records extending to the 1990's at best. Therefore, a comparison of proxy records alone must be restricted to a comparison of 1980's temperatures to past temperatures, which as you point out, show near equality. But, we know from the instrumental record that the 2000's are substantially warmer than the 1980's. To insist that we should then ignore that additional knowledge is specious, and if we do not the conclusion that current temperatures are probably warmer any in the MWP or Roman WP follows.

    Of course, ideally we would extend the proxy record to the most recent times with high quality proxies that continue to track local temperatures over the whole calibration period. Can I expect you to by lobbying your local politician's to pay for just such an effort?

    Having said that, I disagree with the moderator's (DB's) responce. Northern Iberian temperatures are regional temperatures, and by themselves cannot be used as a proxy for global temperatures - a point being well established in the "Core of the Ice" threads.
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    Moderator Response: [DB] I'm sorry, Tom, if that is how that is being interpreted. My intent was to compare the Iberian data only to "the MWP is warmer" claim. Your entire statement here is 100% correct. I have added a clarification to my response to angusmac accordingly.
  34. angusmac @132,

    To further Tom's point, consider also this statement from the Ljungqvist paper:

    The proxy reconstruction itself does not show such an unprecedented warming but we must consider that only a few records used in the reconstruction extend into the 1990s. (emphasis mine)

    Furthermore it is quite clear that no reconstructed data in this case was available for the 2000s. Given that it is now 2011, the assertion that "if you compare proxies with proxies ... the MWP was as hot as today" is not and more importantly cannot be supported by the proxy data alone.
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  35. Moderator @132, new data is always welcome. However, the purpose of my post was to show that you could use the data presented in Dana's post and come to a completely different conclusion.

    Tom @133 and Anonymous @134, I agree that we need more up to date proxies. This should be a high priority in the paleo community. Nevertheless, Table 1 of Ljungqvist (2010) shows that 10 of the 24 proxies used by him extend to 1999 thus including the very hot year of 1998.

    Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998.
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  36. angusmac @135, the data may include 1998, but Lundquvist reports decadal averages. The early 1990's was quite cool compared to 1998, so there is still a sharp difference in temperature. The difference between the decadal average of GISStemp for 1990-1999 and 2000-2009 is 0.18 degrees, sufficient to lift recent tempertures well above the peak decadal average for the MWP (0.15 degrees greater than 1990's). Of course, that is the difference in global temperatures. The difference in NH extra tropical temperatures is likely to be far greater, and would show a correspondingly greater increase.
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  37. angusmac> Consequently, it is not unreasonable to conclude from Ljungqvist's reconstruction that the MWP was as warm as 1998.

    Considering that Ljungqvist used decadal averages (as Tom pointed out), it would indeed be unreasonable and quite inaccurate to draw this conclusion.
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  38. @ Moderator in message #133:
    So? NH extratropical includes europe therefore it is already accounted for. No reason to choose spesific locations which represent only a small fraction of the globe.
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  39. Tom @ 136 and Anom @137, I agree that I should be using decadal averages nevertheless it doesn't change the outcome of my argument as shown below.



    I have plotted the MWP peak temperature as the red line and the modern peak as the blue line on Ljungqvist's (2010) temperature reconstruction in Figure C and it is evident that the MWP peak is 0.11 °C warmer than the modern peak, i.e. the MWP was warmer than the 1990-1999 mean temperature.

    Tom, I also agree that the GISS data show that 2000-2009 mean temperature is 0.18°C higher than 1990-1999. Now, if I assume that the proxy temperatures respond linearly with actual temperatures, the 2000-2009 peak would be 0.18 - 0.11 = 0.07°C higher than the MWP. This is hardly unprecedented warming and is about one-ninth of the 0.6 °C figure stated by Dana.

    Finally, the assumption that proxies would increase linearly from the 1990's to the 2000's questionable because, "…recent proxy data does not emulate the recent instrumental data" (Ljungqvist, 2010). Proxy temperatures are much lower than the corresponding present-day instrumental temperatures (see Figure A in #132) i.e., the so-called divergence problem. What we really need are present-day proxies so that we can compare the current warm period with the earlier proxies.
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