RealClimate logo

National Academies Synthesis Report

Filed under: — group @ 22 June 2006

The long-awaited NAS synthesis report on surface temperature reconstructions over the last few millennia is being released today. It’s a long (155 page) report and will take a while to digest, but we applaud the committee for having tried to master a dense thicket of publications and materials on the subject over a relatively short time.

It is probably expecting too much for one report might to put to rest all the outstanding issues in a still-developing field. And given the considerable length of the report, we have little doubt that keen contrarians will be able to mine the report for skeptical-sounding sentences and cherry-pick the findings. However, it is the big picture conclusions that have the most relevance for the lay public and policymakers, and it is re-assuring (and unsurprising) to see that the panel has found reason to support the key mainstream findings of past research, including points that we have highlighted previously:

1) The authors of the report accurately report the considerable uncertainties that were acknowledged by seminal earlier studies. In particular, Mann et al 1999, which was entitled (emphasis added) “Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations, emphasized the uncertainties and caveats, particularly with regard to reconstructing large-scale surface temperature patterns prior to about AD 1600

The report makes due note of this (pg. 119 of the report):

The Mann et al. large-scale surface temperature reconstructions were the first to include explicit statistical error bars, which provide an indication of the confidence that can be placed in the results. In the Mann et al. work, the error bars were relatively small back to about A.D. 1600, but much larger for A.D. 1000–1600. The lower precision during earlier times is caused primarily by the limited availability of annually resolved paleoclimate data: That is, the farther back in time, the harder it is to find evidence that provides reliable annual information. For the period before about A.D. 900, annual data series are very few in number, and the non-annually resolved data used in reconstructions introduce additional uncertainties.

2) The authors accurately note that, despite those uncertainties, the key conclusions reached by those studies (i.e., that hemispheric-scale warmth in recent decades is likely unprecedented over at last the past millennium) have been substantiated by many other studies, and the confidence in those conclusions appears greater, not lesser, after nearly an additional decade of research (pg. 109 of the report):

The basic conclusion of Mann et al. (1998, 1999) was that the late 20th century warmth in the Northern Hemisphere was unprecedented during at least the last 1,000 years. This conclusion has subsequently been supported by an array of evidence that includes the additional large-scale surface temperature reconstructions and documentation of the spatial coherence of recent warming described above (Cook et al. 2004, Moberg et al. 2005, Rutherford et al. 2005, D’Arrigo et al. 2006, Osborn and Briffa 2006, Wahl and Ammann in press), and also the pronounced changes in a variety of local proxy indicators described in previous chapters (e.g., Thompson et al. in press). Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium.

3) Despite the attempts of some commentators to attempt conflate the evidence for the existence of human influences on climate with the validity of a single reconstruction (e.g. that of Mann et al) it is quite clear that the evidence for anthropogenic impacts on climate is quite strong irrespective of whether or not the original “hockey stick” is correct. The report makes repeated note of this key point, for example on page 4 of the report:

Surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence.

and again on page 9 of the report:

The reconstruction produced by Dr. Mann and his colleagues was just one step in a long process of research, and it is not (as sometimes presented) a clinching argument for anthropogenic global warming, but rather one of many independent lines of research on global climate change.

4) That it is time for the paleoclimate research community to move ahead of the now tired debates about the ‘Hockey Stick”. The authors, as most scientists currently working in the field, recognize the need to work to reduce current uncertainties by aiming to:

  1. obtain additional, improved, and updated paleoclimate proxies of past climate that can aid in decreasing the existing uncertainties,
  2. focus greater attention on the relative strengths and weaknesses of alternative types of proxy information such as tree-ring, corals, and ice cores (see e.g. here and here) so that more robust climate reconstructions can be formed making use of complementary information available from “multi-proxy” networks,
  3. pay attention to legitimate (rather than specious, e.g. here and here) issues with regard to the strengths and weaknesses of alternative paleoclimate proxy reconstruction methods [it was encouraging, for example, that the authors of the report favor the use of some combination of the standard measures of the fidelity or "skill" of paleoclimate reconstructions ("RE" and "CE") generally used by paleoclimate researchers, and dismiss as without merit the use of simple correlation coefficients], and
  4. move beyond the often inappropriate focus given to hemispheric mean temperature, and give greater future attention to the detailed spatial patterns of past temperature changes, as well as reconstructions of precipitation and atmospheric circulation variables. These can provide greater insight into the underlying dynamics of the climate system and the key role that dynamical modes such as the El Nino/Southern Oscillation may play in climate change.

While we agree with the bottom-line conclusions in the report, this is not to say that we don’t also have some criticisms:

The report provides an unbalanced discussion of some significant technical details. For example, there is quite a bit of discussion of possible biases involved in centering conventions used in Principal Component Analysis (PCA). Yet the report only vaguely alludes to the fact that published work [see both Wahl and Ammann (2006) and Rutherford et al (2005) cited in the report] clearly demonstrates that this doesn’t introduce any significant bias as long as statistically significant patterns in the data are not discarded.

The report calls into question the confidence in certain fairly specific previous conclusions, e.g. the tentative conclusion in Mann et al (1999) that the 1990s and 1998 were the warmest decade and year, respectively, of the past 1000 years. There are two important points here left unmentioned in the report: (1) Mann et al (1999) attached the qualifier “likely” to these conclusions, which in standard (e.g. IPCC) parlance corresponds to a roughly 2/3 probability, i.e., implies slightly better than even odds of being true, a fairly conservative conclusion. The conclusion was followed by the statement “More widespread high-resolution data which can resolve millennial-scale variability are needed before more confident conclusions can be reached…”. (2) The conclusions regarding the decade of the 1990s and the year 1998 follow from reasonable assumptions. The late 20th century Northern Hemisphere average warmth, according to Mann et al (1999) and all subsequent studies, appears anomalous in at least the past 1000 years. So the base state about which higher-frequency (e.g. interannual) fluctuations occur was substantially higher at the end of the late 20th century then during any earlier comparable period. Unless the interannual fluctuations in hemispheric mean temperature during earlier centuries were significantly greater in amplitude than during the 20th century (and there is no obvious evidence that they were), then it reasonably follows that the thresholds reached during the 1990s or during 1998–an anomalously warm decade and year respectively from the perspective of the instrumental record–are unlikely to have been breached in earlier centuries.

The committee does not seem to have grasped fully the significance of some very recently published results that are cited in the report, notably the papers by Rutherford et al (2005) and Wahl and Amman (2006) that further demonstrate the robustness of the Mann et al (1998;1999) conclusions and subject some published criticisms of those conclusions to rigorous scrutiny. The authors cite somewhat uncritically the Von Storch et al (2004) study arguing that climate field reconstruction techniques can significantly underestimate long-term trends, despite the fact that errors have now been acknowledged in that study (see here and here), and that an independent study not cited, but published well before the report was drafted, comes to very different conclusions. This reflects one of a number of inevitable minor holes in this quickly prepared report.

One of our main criticisms though doesn’t involve the report itself, but the press release that accompanied it. We’ve noted before the importance of making sure that the press will be able to correctly contextualise a release and the bad consequences of that not happening. Well, in this case the press release annoucing the publication of the report was often inconsistent with what was actually stated in the report. It was titled: ‘High Confidence’ That Planet Is Warmest in 400 Years; Less Confidence in Temperature Reconstructions Prior to 1600 which is not news at all and almost trivially true. However, it is likely to be mis-interpreted to imply that there is no confidence in reconstructions prior to 1600, which is the opposite of the conclusion of the report. Additionally, the text appears to have confused the key distinction between our knowledge of global mean temperature in past centuries (which is very limited owing to the sparseness of long available proxy data in the Southern Hemisphere, and for which a reconstruction was not attempted by Mann et al or most other researchers), with our knowledge of Northern Hemisphere mean temperature (which is considerably better; hence the emphasis of this quantity in past work).

Finally, it is worth pointing out and emphasising that the report provides absolutely no support for the oft-heard claims that the original hockey stick was the result of ‘programming errors’, or was ‘not reproducible’, or there was some scientific misconduct involved. These claims were always spurious and should now finally be laid to rest. Hopefully, we can all start to move forward with the science again.

81 Responses to “National Academies Synthesis Report”

  1. 1
    Mark Lynas says:

    “…the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium.[emphasis added]” Plausible? That’s not a very strong word. In IPCC-probability terms it must rank well below ‘likely’ (66-90% probable) and I guess even below ‘medium likelihood’ (33-66% probable). Hardly a ringing endorsement – which I think is a shame, because as the posting says, the basic conclusion of unprecedented global warming during the millennium is supported by a whole raft of other studies. Again, my feeling is that there’s a lot more politics here than science.

    [Response:According to the statements in the press conference, they chose 'plausible' becuase they didn't want to quantify likelihood a la IPCC, but I would read it as equivalent to 'likely', which is of course what MBH said all along. - gavin]

  2. 2
    Sean Houlihane says:

    So, if I read the press release accurately, they say that there was a significant cool period (LIA), and there is high confidence that recent temperatures are higher than that period. They also say there was a warmer period at approx 1000 AD, but uncertainties in the reconstructions make it unclear if that period was warmer than today or not.

    The part which we have high confidence in appears to say little about todays climate in a long-term sense, but your comentary suggests that this is a significant finding – and dismisses the uncertainty about the difference between 1000 AD and 2000 AD temperatures.

    Is not the latter the more significant data point? The press release does emphasise that further research on this datum seems valuable..


    [Response: I don't think you read it correctly. The claim is that we know more about the situation over the last 400 years than for the previous period (which is obvious), but that only before 900 AD is the data basically useless for the NH mean. From the report and press conference, it is clear that they are saying that it is indeed likely that it is warmer now than 1000 years ago, but that is not as strong a statement as you can make for the last 400 years. Reducing the uncertainties further would of course be useful. Who implied that it wouldn't be? - gavin]

  3. 3
    Michael Jankowski says:

    “obtain additional, improved, and updated paleoclimate proxies of past climate that can aid in decreasing the existing uncertainties”
    That’s an interesting one – ClimateAudit has been calling for “bring the proxies up to date” for some time. It’s nice to see that both CA and RC share some common ground!

    I’d add to it that the sharing of data and methods would also be helpful. The NAS report does touch upon that issue somewhat, but not enough.

    Re:#1 (gavin): “According to the statements in the press conference, they chose ‘plausible’ becuase they didn’t want to quantify likelihood a la IPCC, but I would read it as equivalent to ‘likely’, which is of course what MBH said all along.”
    The sentences following the quote from #1 (NAS report page 4) suggest they weren’t equating the two:

    The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we placed in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millenium.”

    So their use of “plausible” seems to contain a lot more doubt than the “likely” used in the MBH sense. But maybe it’s just all semantics.

    [Response: It's unfortunate that the committee did it like this. IPCC authors have spent a lot of time moving towards more precise language when communicating the strength of the belief of expert judgments, and I'd been under the impression that the bulk of the community was following this trend. However, the reversion to poorly defined ambigious language in this report seems to belie that. However, in the case of the 'late 20th C warmer that any period over the millennium' claim, the panel specifically gave roughly 2:1 odds in favour of the statement being true in the press conference and that translates directly to the IPCC 'likely' designation. - gavin]

  4. 4
    Paul Biggs says:

    I downloaded a free copy. So, it is ‘plausible’ that the MWP was not as warm as the current warm period. This is one of those reports with something for everyone – criticism of methods and data, plus a rather half-baked call for data release:

    “Our view is that all research benefits from full and open access to published datasets and that a clear explanation of analytical methods is mandatory. Peers should have access to the information needed to reproduce published results, so that increased confidence in the outcome of the study can be generated inside and outside the scientific community. Other committees and organizations have produced an extensive body of literature on the importance of open access to scientific data and on the related guidelines for data archiving and data access (e.g., NRC 1995).”……

    Obviously there was a higher confidence in the less contentious LIA, than the MWP, so I think the controversy over the MWP is set to continue, particularly as most of the criticisms of MBH were accepted by the panel. Overall I feel, the NAS panel failed to ‘grasp the nettle,’ but have moved the debate forward.

  5. 5
    Bryn Hughes says:

    So that we can say that we are not absolutely certain that the 1990s were warmer than the MWP

    [Response: Absolutely certainty exists only in mathematics, not the real world. -gavin]

  6. 6
    Rod Brick says:

    Why is it that science that agrees with our own notions (preconceived or studied) is precise and solid, and that which doesn’t is politics?

    [Response: Why is this asked whenever the scientific consensus comes up with a statement someone doesn't like? -gavin]

  7. 7
    Brad Hudson says:

    I’m just an ordinary non-scientist trying to sort all this stuff out. This site has been invaluable in helping me understand the science. I read the press release and then the conclusions section of the report. I found the form of the conclusions both confusing and disappointing. The report never explains what it means by “high level of confidence”, “less confident” or “plausible.” Listening to the press conference, I understand that the first term means something like 90-95% confidence, the second means 2:1 odds, and the third means “we can’t quantify it at all.” I dont’ pretend to understand all the technical details in the report, but is it too much for us lay folks to expect some degree of precision and clarity in the conclusions of a report of this type?

    [Response: Agreed! -gavin]

  8. 8
    Bryan Smith says:

    Is there any current way to better assess temperatures from more than 400 years ago or do more studies using current proxy methods just need to be done?

    [Response: Fund more science to gather more proxies? And to research new ones... - William]

  9. 9
    lars says:

    So why is there also global warming on Mars?
    Why does this not address global overpopulation of say the billion plus Chinese, Indians, Muslims? At what population (human and animal) level does the earth need to be reduced to based on this study?
    Why does this not address the global warming that has occurred since the last ice age, which I find ice ages more of a problem then global warming. There have been 60 glacial advances and retreats in the last 2 million years as noted in the link below. Why does this not address eccentricity of the earth’s orbit, the tilt of the earth’s axis, and the precession of the equinoxes? Or even plate tectonics, continental uplift, reduction of CO2, and changes in the earth’s orbit? All contributors to climate changes.

    During each of these intervals, many glacial advances and retreatsoccurred. For example, over 60 glacial advances and retreats have occurred during the last 2 million years.
    If “ice age” is used to refer to long, generally cool, intervals during which glaciers advance and retreat, we are still in one today. Our modern climate represents a very short, warm period between glacial advances.

    Learn about plate techtonics, continental uplift, reduction of CO2, and changes in the earth’s orbit.

    Learn about the eccentricity of the earth’s orbit, the tilt of the earth’s axis, and the precession of the equinoxes

    [Response: Why do you not address all the other topics of potential concern? Why do you not look at the index? Learn about the terms of reference... ;) - gavin]

    [Response: Re GW on Mars... we've done this already: here - William]

  10. 10
    Paul Biggs says:

    There is another MWP proxy – vineyards – The History of the Wine Trade in England by A L Simon, 1906:

    “Towards the middle of the twelfth century, we are told by William of Malmesbury, vineyards were no longer confined to a few places, but extended over large tracts of country, producing a great quantity of excellent wine: “You may behold,” he observes, when describing the fertility of the vale at Gloucester, “the paths and public roads fenced with apple trees, which are not planted by the hand of man but grow spontaneously. …”

    “This district, too, exhibits a greater number of vineyards than any other county in England, yielding abundant crops and of superior quality; nor are the wines made here by any means harsh or ungrateful to the palate, for, in point of sweetness, they may almost bear comparison with the growths of France.”

    In the reign of Stephen, there is a mention, in 1140, of two vineyards at Mealdon, and, in the same year, the Sheriffs of Northamptonshire and Leicestershire were allowed, in their accounts,”for the livery of the King’s vine-dresser at Rockingham, and for necessaries for the vineyards.” There is also an Act of this monarch, which is undated, but which from internal evidence may be safely attributed to A.D. 1143, ordering that restoration should be made to Holy Trinity Priory, London, of its land in Smithfield, which Geoffrey, Earl of Essex, had seized and converted into a vineyard.

    In the fourth year of the reign of Henry II, payments appear to have been made and charged to the Royal Exchequer for the keeper of the vineyard, who received on one occasion sixty shillings and tenpence, as well as for the expenses of the said royal vineyard. Later on, during the same reign, in 1159, 1162, 1165, 1168, 1174 and 1175, there are frequent mentions of the royal vineyards at Windsor, Purley, Stoke, Cistelet, and in Herefordshire and Huntingdonshire; in 1165, there is an entry of a vineyard at Tenham, the produce of which seems to have been devoted to the sick at the infirmary.

    During the first year of the reign of King Richard, there are three mentions of vineyards, and others occur during the reigns of Henry III., at Lincoln, Bath and Hereford, of Edward II at York, and as late as that of Richard II., in 1385 and 1392, at Windsor II and Kennington. At the beginning of Edward I’s reign, in 1276, Cantilupe, Bishop of Hereford, either planted or renewed the vine-yard which his pupil and successor, Swinfield, had at Ledbury. In 1289, the Bishop made seven casks (dolia) of white wine and nearly one of verjuice at Ledbury. This wine was chiefly transferred to Bosbury, another estate of the Bishop, and it was mostly drunk during the ensuing summer.

    Ledbury must have been particularly well suited for the culture of the grape vine, since as late as the end of the seventeenth century,” Ah! – the LIA was bad news for wine production in England, but it is booming again:

    [Response: By that proxy it is clear that it is warmer now since there is more wine produced today than there was 1000 years ago. Still not very good to drink (though I hear there are a few exceptions). - gavin]

  11. 11
    Michael Jankowski says:

    “Response: Absolutely certainty exists only in mathematics, not the real world. -gavin”
    As an applied math major in my undergrad days, I am deeply offended! Plenty of math is “real world!” I think this response should have been censored and the responder warned! :)

    I can say with “absolute certainty” that it’s warmer today where I live (90s) than it was back in December when I was getting snowed on.

  12. 12
    Paul Biggs says:


    Gavin, you are right – I drink Californian.

  13. 13
    Steve Sadlov says:

    RE: #11 – I can say with certainty that after one of the crummiest Springs in recent memory where I’m at, the current outbreak of a dry, compressive interior SW US airmass is really nice. I can also say with certainty that the inevitable coastal stratus and seabreeze that always follow with a vengence will have me breaking out my sweater by some time next week. :)

    Also, for what it’s worth, in this neck of the woods, 1998 was a record cold year, especially in the Fall – snowed down to sea level of the last day of Fall that year. For us, it was 2000 that was the hot one – an interior outbreak hit just right during high sun angle in late May and early June, and it hit 115 F at my place – I have no AC (as is true of 90% of the folks in my immediate locale). Not fun? …. for some actual fun via Google, looking up oddities such as Santa Anas, Sundowners and Diablos, and their ability to transform normally mild coastal areas into a weather pattern that is typically Iraqi, for a couple of days, can be quite interesting. Variation makes life interesting? Perhaps … so long as I can have a cold Margarita!

  14. 14
    Zeke Hausfather says:

    The Times has a story up about the report already.

    While its not a bad piece overall, the part near the end where they cite since-discredited critiques of the original Mann et al. article is rather dissapointing, given that the only reported rebuttle is that the Mann et al. paper made numerous caveats regarding uncertainties.

  15. 15
    Jason Rife says:

    I am having trouble reconciling two points of the report as summarized in an AP article (I am assuming they got the facts right.) Over the last 2000 years, give or take, the earth probably has experienced significant global temperature swings, both hotter and cooler, yet the levels of CO2 and methane have stayed fairly constant over the last 12,000 years, except for the most recent history. This alone would suggest that within the ranges over the last couple of thousand years CO2 and methane levels have had little impact on global temperature. What am I missing?

    [Response: Here are a few things you are missing. First, it's simply not true that there are documented temperature swings in the past 10,000 years that are clearly comparable on the warm side to what has been seen in recent times. It is only for the past 1000 years that one can tentatively estimate hemispheric averages, and there it is increasingly clear that the recent warming is unusual. With regard to earlier times, the main problem is that it is currently not possible to reliably estimate global or hemispheric averages from the proxy data, so it is not possible to say if warming in the earlier Holocene were as widespread as the current warming. That goes especially for the "climatic optimum" in the early Holocene, which is almost certainly due to the Earth's orbital fluctuations --specifically the precessional cycle. There is some global mean signal from the precessional forcing, but theory says the warming should be mostly regional and seasonal -- proxy data is largely silent on how global the real warming was at the time. The second thing you are missing is that there are actually multiple causes of climate change, and the existence of other climate forcings does not in any way negate the importance of CO2. Other things that have varied during the Holocene include volcanic activity, solar activity, and the precessional cycle. Just because some of these things can also cause climate change doesn't mean that CO2 can't. If you can die of cancer, does that mean you can't die of a heart attack? The final thing you neglect is that currently we are only comparing the relatively modest warming so far with the warming of the past several thousand years. However, so far we haven't quite gotten to 400ppm CO2, but we'll eventually go to 700 or more without controls. We haven't even seen the full warming effects of that 400ppm yet, because it takes time for the ocean to warm up. So, the striking thing is that it has already gotten to the point that the recent warming stands out from the natural variability of the past thousand years or more , despite the fact that so far we've only experienced the barest beginnings of the warming. That's not just striking. It ought to be alarming. --raypierre]

  16. 16
    e. ou says:

    In the interest of the public, is it possible for real climate and climate audit to run a parallel analysis of the NAS report. This may not resolve the debate but at least it will give us a more balanced approach than to go through the comments in each of the web sites.

    I doubt if comparing the wine production in UK 1000 years ago and today would be a good proxy that the climate is warmer today. The volume of wine produced is a function of a large number of natural and human factors other than climate. One major factor is the preference to wine and acloholic beverages as well as the human population.

  17. 17
    Joel Shore says:

    Re #14: What you are missing is correct logic. If one variable has remained constant (CO2 levels) while a second (temperature) has varied, you can’t learn anything about the sensitivity of the second to variations in the first…because the 1st hasn’t varied. It could be that temperature is exquisitely sensitive to CO2…In fact, it could even be that the very small changes in CO2 drove those supposed significant temperature swings. [However, in reality, your premises are questionable too. First, while there have been some swings in temperature, the evidence suggests that they have not been that strong. And, while CO2 has been fairly constant, it has not been completely so.]

    Re #10: Maybe I am being ignorant here and someone with more knowledge of wines can clue me in but I have never understood how wine-growing in England is much of a proxy. We grow wine here in upstate New York and I can bet that at least our winter climate is considerably colder than it has ever been in England even during the LIA. I also imagine our growing season is shorter. (Or, is it the summer climate that matters more?)

    [Response: I never much liked wine-growing as a proxy either; it's too confounded by extraneous factors. For example, changes in the demand for liturgical wine, owing to changing religious practices, can alter the profitability of growing local low-quality wine. --raypierre]

  18. 18
    Joel Shore says:

    My above comment referenced to #14 is commenting on Jason Rife’s post which I see is now labeled #15.

  19. 19
    C. W. Magee says:

    re 14.
    Jason, what you are missing is the difference between what is possible and what is probable. Prior to 400 years ago, large swings in temperature cannot be ruled out, because (to grossly simplify) the error bars are too big for the older reconstructions. This does not mean that large changes did occur during that time period. It just means that today’s body of knowledge is not sufficient to exclude large changes. Wheras for the last 400 years, we have enough data to say with some measure of confidence that variations were relatively minor.

    re grapes.
    Are grapes a proxy for growing season, winter minimum temperatures, or socioeconomic/religious/political factors? How does one deconvolve 17th century cooling from Cromwell’s puritanism?

  20. 20
    Jihye Yin says:

    Could you please respond to some of the comments on the press conference, as summarized e.g. here?

    The NAS panelists said that the principal component method was incorrectly used in that context. The climate before 1600 was almost entirely uncertain and even the level of confidence can’t be quantified. The MBH results were oversold by the community. The divergence problem exists and does not want to go away. The uncertainty and natural variations are larger than thought previously.

    Are the NAS members wrong? Are all of them paid by ExxonMobil as I believe?

    [Response: Read the report itself, not Lubos Motl's blog. Motl's take on the report has almost no resemblance to what is in it. What do you expect from somebody who describes himself as a "reactionary physicist"? Unfortunately, some un-necessarily ambiguous wording at the press conference makes it all too easy for people like Motl to misrepresent the contents. --raypierre]

  21. 21
    Chuck Booth says:

    Re: #11 “I can say with “absolute certainty” that it’s warmer today where I live (90s) than it was back in December when I was getting snowed on.

    Can you provide some mathematical precision to that qualitative assessment?

  22. 22
    Leonard Evens says:

    Re 11:

    We are getting off topic again. In mathematics you can prove something and be certain it is correct, subject of course to possible mistakes in the proof, in the sense that the conclusion follows logically from the assumptions. A model for this is Euclidean geometry, which is as true now as it was over 2000 years ago. But as a statement about the actual geomtry of the world, we know it is false. In science, you are more concerned with conforming to observation, and you may even in some cases accept arguments which don’t stand up to the requirements of mathematical rigor, as long as they make accurate predictions.. (You sometimes do that also in applied mathematics.) I believe that is the distinction that Gavin was trying to make. You can’t expect the kind of certainty you find in pure mathematics in any science, particularly a messy one like climatology where you have to bring together many different kinds of evidence. That doesn’t of course mean that anything goes. There are rather severe restrictions on what can pass as an acceptable argument. But it is not an axiomatic system.

  23. 23
    Bob Burnier says:

    I have just begun to take a look at the scientific debate on global warming. I am no climatologist but rather an individual with a doctorate in chemistry. What I find interesting is the focus by everyone on the term “warming” and all this effort at looking at historical temperatures. The relevant parameter to me is the amount of heat our global system has at any point in time. If you add heat to an ice cube, the temperature of the ice cube does not change. The heat is used to melt the ice and during this process of melting the temperature stays constant. This temperature is called the melting point or freezing point of the substance – in this case water. Once the ice has melted, the temperature of the water will rise depending on the amount of heat entering the system, the heat capacity of water, etc. So, if the earth retains more heat because of rising greenhouse gases, water temperatures may not rise signifcantly because the heat is used in melting ice. If all the ice melts, water temperatures will rise in accordance with the amoount of heat being absorbed and stored by the system (oceans, land, and air). From what I have seen, we have lost a fair amount of glacial and perhaps polar ice over the last thirty years or so. This means more to me than a debatable one degree rise in average ocean temperature over the last one hundred years. If the ice goes, temperature rise will be self evident. Perhaps some of the scientific committees should add a few physical chemists to their panel discussions.

  24. 24
    Wolfgang Flamme says:

    “The National Academy scientists concluded that the Mann-Bradley-Hughes research from the late 1990s was “likely” to be true, said John “Mike” Wallace, an atmospheric sciences professor at the University of Washington and a panel member. The conclusions from the ’90s research “are very close to being right” and are supported by even more recent data, Wallace said.”

    No more funding, no more research needed. Just ask Wallace since he’s the one knowing right from wrong.

    [Response: Mike Wallace is one of the clearest thinkers in the field, a National Academy member and author of dozens of highly influential papers. Respect for his point of view (though not mandatory) is highly recommended. He does not make such pronouncements lightly. -gavin]

  25. 25
    Paul Biggs says:

    Please don’t take my ‘vineyard proxy’ post too seriously, it was meant to be light-hearted, but it does indicate that Ledbury was particularly kind to the grape vine from the 13th century onwards until the end of the 17th century, which would coincide with the ‘maunder minimum.’ The current UK warm period peaked in 1997 (Armagh Observatory), and 1999 (Hadley CET)in our two long temperature series. I don’t see 2006 beating those annual average temperatures, but we’ll have to wait and see what happens in future years. Breaking the 11C barrier for an annual average would certainly be instrumentally unprecedented in the UK.

  26. 26
    pete best says:

    The UK now has some 400 vinyards but as you can appreciate the best ones lie in the deep south of the UK and have indeed WON awards especially in the sparkling wine categories. I have visited many of them and indeed the growing season appears to be around 1 month longer than it was in the year 1900. Indeed so popular has English Fizz become that the californians and the French Champagne makers are looking at buying land in the south of the UK in order to grow grapes and makes good fizz/bubbly.

    Anyway onto the subject at hand. Fred Pearce in his book “the Last generation” devotes a chapter to this hockey stick proxy subject and states that the proxy data used has been suject to reanalysis and has been declared to be sufficiently (statisticlly) accurate that I thought that the subject has been laid to rest.

    Indeed Realclimate has also made comment on this subject in relation to the climate skeptics and have also stated that independent reanalysis of the statistical data shows it to be accurate and correct within normal error thresholds.

    Indeed the book even quotes Gavin at one point so I guess you guys at real climate know Fred Pearce?

  27. 27

    I just ran across a paper from 1991 which seems to make a devastatingly impressive case that Solar activity has caused recent global warming. Amazingly, it’s not by Soon and Baliunas. Can anyone take a look at this and tell me where the mistakes, if any, lie? I assume this has since been discredited but I don’t know the details.

    [Response: Devastating? Try made up. The figure only looks so good because the smoothing they use changes as you go along. With 15 years more data and uniform data treatment the correlation disappears. I would judge this the best example of researchers fooling themselves into finding what they wanted to find before they started. Read Damon and Laut (2004) for the details (and other examples). - gavin]

  28. 28
    Leonard Evens says:

    Re 23:

    Perhaps a physical chemist just beginning to study the subject should do some more research before giving advice. A good place to start would be the IPCC reports, but much has happened since the last report. There are variety of factors which lead to delays in warming, one of which is the one he points to, and those who do research in the area, including, the Real Climate scientists are well aware of them.

    [Response: That's a little harsh. A pointer to some of the existing work on heat content changes would be more constructive! (try Levitus et al (2001?) and Hansen et al (2005) for instance). - gavin]

  29. 29
    Coby says:

    Re #23,

    You have a reasonable point here and it is not one nobody else has thought of. There is however good reason to focus on surface temperature and that is the simple fact that the surface is where we all live. It is also where the vast majorty of the biosphere exists if we extend it into the the upper ocean. You could also fundamentally alter the system simply by redistrubuting the heat, no net change required. So a total heat content metric is a good one, but I would argue that the change in surface temperature is more appropriate for policy discussion and impact assessments.

    [Response: Indeed it's a reasonable point, and indeed it's already incorporated into calculations of climate change, though not necessarily into public communication about the results. The energy needed to melt ice, whether sea ice or land ice, is part of the thermal inertia of the system that slows the approach to equilibrium. The major term in the thermal inertia is the time required to warm the deeper ocean. So, properly speaking, the effect of added greenhouse gases shows up partly as warming and partly as melting, and that warming shows up partly as surface warming and partly as deep ocean warming -- until the system reaches equilibrium. With regard to the suggestion in the original post, the basic calculations on the physics of planetary climate have rested on energy balance ever since Fourier's 1827 paper. --raypierre]

  30. 30
    Jean-Luc P says:

    Reply to Bob Burnier :

    The fact is that exchange rate of heat are more a limitation at this scale than at your drinking glass scale : so your interresting naive analysis of why temperature don’t increase so much is maybe not very relevant because of that.

  31. 31
    esrc_fan says:

    In addition to the references given by Gavin regarding the heat content in the ocean. Levitus has a paper in GRL Levitus (2005) on climate subsystems heat content. Continental subsurface heat content has been addressed by Beltrami et al. (2002), Beltrami (2002) and more recently in Beltrami et al. (2005) .

  32. 32
    Doug Percival says:

    raypierre wrote in response to #15:

    However, so far we haven’t quite gotten to 400ppm CO2, but we’ll eventually go to 700 or more without controls. We haven’t even seen the full warming effects of that 400ppm yet, because it takes time for the ocean to warm up. So, the striking thing is that it has already gotten to the point that the recent warming stands out from the natural variability of the past thousand years or more, despite the fact that so far we’ve only experienced the barest beginnings of the warming. That’s not just striking. It ought to be alarming.

    It is not only alarming, it is outright terrifying. And that, along with the self-reinforcing feedbacks that the “barest beginnings of the warming” are already apparently triggering — increased heat absorption by ice-free arctic oceans, release of carbon and methane from warming soils, etc. — is what makes me skeptical of the view expressed by Al Gore and others that we still have some ten years in which to prevent irreversible, catastrophic, runaway warming, and not only “climate change” but a global ecological collapse. I find it hard to see how we have not already passed the point of no return.

  33. 33
    Tom McKissic says:

    I do not understand why it is not rational to question models and trends which are being used to predict unkown future conditions but it remains perfectly acceptable to dismiss past, 10,000 year B.P., proxy data which may conflict with present models.

    I realize proxy data is limited at this time, particulary for the southern hemisphere, but the existing data should not be ignored just to make recent history models stand up. I welcome the day when sufficient data has been collected so a confident model can be created which, when fed data up to a past point, can accurately predict past temperatures.

    [Response: What is being ignored? And what do you feel is inconsistent with the models? Simulations for mid-Holocene conditions driven mainly by orbital forcing do a good job of matching the obs. - gavin]

  34. 34
    Tom McKissic says:

    Your response supports my point. Certain simulations based on certain conditions match certain observations but a “golden rule” has not yet been created. The models “driven mainly by orbital forcing” are not the models currently being touted as future predictors of climate (in most cases solar influence is being ruled inconsequential for current conditions). So far, in order to match accepted historic and prehistoric observations something has to be ignored.

    The stakes are high for supporting either side of the global warming issue. Regardless of the point you are arguing it is irresponsible to dismiss alternate views when there are still so many unknowns. Remember it was once “the scientific consensus” the sun orbited the earth, the world was flat, the sound barrier was unbreakable…

    I agree with Williams response above – fund more research for creating more accurate models. Who knows, we may find we should be heading colder and the only thing maintaining temperature is Co2.

    [Response: You have it completely wrong. The state-of-the-art models used for the 20th Century and future simulations are exactly the same ones that are being tested using paleo-climate conditions. Look up PMIP II for instance. At different times in the past different things were going on, and some are more important on some timescales than others. There is no 'golden rule'! Instead there is a complex system that can be pushed around by multiple different forces - including orbital variations, solar variability, the opening of ocean gateways, volcanoes and, yes, greenhouse gases. For the current situation: orbital forcing is very small and so doesn't play much of a role, solar variation is, as far as we can tell, a minor player, GHGs are a big factor, and so are aerosols, ozone, volcanoes, land use are all also minor but necessary. Why do you think things are being ignored? All of these things are tested to see if they are important, and the ones that are, are kept in. - gavin]

  35. 35
    Eli Rabett says:

    Paul Biggs need not apologize, Pfister’s record of monthly precipitation in Central Europe 1525-1979 does include information from diaries recording the time when grape vines blossemed and the grapes were ripe.

  36. 36
    Tom McKissic says:

    Your use of the absolute, completely, emphasizes my argument that no side should be closed and imflamatory. Ignore my use of term “golden rule” and acknowledge YES there is a mathematical equivalent for all the complex factors driving climate. An accurate model has just not yet been created. Your statement “All of these things are tested to see if they are important, and the ones that are, are kept in.” implies some things are left out. All influences, if found to be important at any time, have the potential to be important in the future. There are way to many unkown interactions in the complex system to leave out certain influences. It should be everyones goal to keep updating and improving models regardless of the findings. My concern is the tendancy of those with extreme support of current global warming understanding as an absolute to villanize others with legitimate questions – realizing there are those types on both sides but pro warming has the stage right now.

    I agree there is currently work being done to make a more comprehensive model which address past and present conditions in order to accurately predict future changes but disagree there is a working model with published results clearly matching early and current observations. It is a frustrating data search when the vast majority of supporting information focuses on the last 1000 years and contrary information focuses on the paleo. I, like many others, am only asking for a link before jumping on the bandwagon of industrial reform. With proper support and open minded researchers (or at least the teaming of opposites) to tackle the endeavor this should not substantially delay any needed social change and could actually result in faster change if universally supported.

    [Response: Oh, please.... If you would get off your high horse for a second and you would see that testing against paleo-data and putting in of new physics is what we actually do all the time (check out my own publication list for instance - you'll find solar and volcanic and mid-Holocene and LGM and PETM and Cretaceous...). - gavin]

  37. 37
    Don Baccus says:

    An accurate model has just not yet been created. Your statement “All of these things are tested to see if they are important, and the ones that are, are kept in.” implies some things are left out. All influences, if found to be important at any time, have the potential to be important in the future.

    If rational simplifications of mathematical models disturb you so, may I humbly suggest you never step foot upon a Boeing 787?

  38. 38
    Tom McKissic says:

    Thanks for the personal attack. Models are being tested, putting in and taking out of factors and many are good at matching certain timescales but nothing has been found to model accurately accross all timescales with known information. Yet many are taking data produced and circulating it as fact when even the persons generating the data referencing probabilities. All I’m asking is the same effort be put into research as is currently put into marketing certain findings and suggested responses.

  39. 39

    Re #36 — there is the “Millenium Project” now that will have various modelling groups do the last millenium. Most groups do hindcasts over a period ranging from 50 to a few hundred years (i.e. covered by the “high probability MBH98 area” and HadCRU etc). For example my own project is currently doing a 1920-2000 hindcast and a 2000-2080 forecast in a large ensemble using the HadCM3 model, to quantify uncertainties in the model, try a large range of parameters etc. You really need to look at the actual literature & work done rather than jump to false conclusions.

  40. 40
    Tom McKissic says:

    Simplifications are fine if they return results that match observed occurences – and not just for certain conditions or timeframes. Boeing models work just as well at 500 feet as they do at 30,000 feet, over all temperature ranges and all forces – if they didn’t planes would fall out of the sky. Accurate models (even simplified) provide accurate results. All I ask is the same be applied for climate research. Thanks for the comparison.

  41. 41
    Don Baccus says:

    All I ask is the same be applied for climate research.

    And your posts make it clear you have no basis for assuming they don’t, given your lack of knowledge as to what’s being done. It appears that you’re one of those who assume the models aren’t accurate because you don’t like the implications of the results.

  42. 42
    lars says:

    and what of this?

    this shows co2 levels and temperature within historic norm for the last 400,000 years.

    [Response: Wrong. It shows that CO2 levels didn't breach 300 ppmv in 400,000 years until now - currently 380ppm and rising. -gavin]

  43. 43
    Gar Lipow says:

    >…is what makes me skeptical of the view expressed by Al Gore and others that we still have some ten years in which to prevent irreversible, catastrophic, runaway warming, and not only “climate change” but a global ecological collapse. I find it hard to see how we have not already passed the point of no return.

    32 is a very important point to reply to. So far when I encounter it I refer people to the following:

    But I really wish I could come up with a short reply – if not a soundbite, than maybe a few paragraphs.

  44. 44

    (1) A reading of today’s NY Times…
    …on the NAS climate report demonstrates clearly that Inhofe, Barton, and their familiars have decided to continue to focus on the Mann paper, as if nothing else has happened since. This is a political decision, not a scientific one.

    The next and most interesting question would be how the NY Times reporters decided upon this emphasis. Is this from a press release from the contrarians? Will they please explain themselves?

    (2) Re: 42. Gar Lipow, Stephen Hawking just stated he is “very worried about global warming.” He said he was afraid that Earth “might end up like Venus, at 250 degrees centigrade and raining sulfuric acid.” See:

    (3) Re: 40. Tom McKissic, why don’t you state what you know about how Newton’s theory of gravitation is applied to the solar system, so it can be illustrated how the scientific method is identical to this on the climate, with additional further complexities.

  45. 45
    Gar Lipow says:

    > Gar Lipow, Stephen Hawking just stated he is “very worried about global warming.” He said he was afraid that Earth “might end up like Venus, at 250 degrees centigrade and raining sulfuric acid.” See:

    You will note that Hawking gives no reason for thinking this could happen. Global warming is bad – but not infinitely bad. When you start talking about stuff like “250 degrees centigrade and raining sulfuric acid” you need to explain; if simple assertion was enough, then Hawkng could go further and assert that global warming will

    >Go Down Angel, Consume the flood
    >Snuff out the sun, turn the moon the blood
    >Go Down Angel shut the door
    >Time has been, shan’t be no more

  46. 46
    John L. McCormick says:

    RE: #43, Gar, I am also skeptical of the view of Al Gore that we still have some ten years in which to prevent……

    For one, I see measured global CO2 emissions increasing about a billion tons 2003 to 2005 — about 2 percent annual growth rate. Carry that out to 2015 and we see global CO2 emissions at 34.242 billion tons or a 25 percent increase from 2005 total.

    In these ten years China and India will continue investing in conventional power generation equipment and vehicles. There is nothing else commercially available to steer the growth projection down….and to those quick to offer solar panels, wind turbines, hybrid vehicles as their alternative to the India-China markets, I say bring back the purchase orders and I’ll listen to your challenge of my pessimistic view.

    Finally, the oceans, ice and biosphere already affected by the current 381 ppm MLO CO2 concentration increasing at 2.5 to 3 ppm/yr over the coming decade will have to accommodate between 25 and 30 ppm more CO2 in 2015. And, that (only the measure of fossil fuel consumption) is not accounting for the fact, as some predict, the Northern Passage may be ice free by 2015 and thus, further loss of Arctic ice albedo.

    Yes, the public has to believe there is time to turn back the big energy knob before it takes us to a point of no return.

    But, those who devote their training and expertise to understanding climate change have an obligation to also challenge policy makers and social scientists to consider it is time to consider what to do in the event of worst case (runaway climate change driven by positive feedback of CO2 and methane).

    We, nations in the North and South, will need guidance to determine what will be needed to adapt to warmer, dryer climates and particularly those providing grain for the world. How about a serious discussion about lead times to develop modified crops capable of withstanding much harsher growing conditions in drought-stressed North America and the Ganges Delta.

    What measures must we now begin to apply to adapt (and we will adapt, if only by cranking up our air conditioner) to short-term increasingly unpredictable weather patterns and long-term breakdown in civil structures? It may not be as stimulating as discussing use of tree-ring proxies but it is valid and essential nonetheless.

  47. 47
    Don Baccus says:

    “A reading of today’s NY Times on the NAS climate report demonstrates clearly that Inhofe, Barton, and their familiars have decided to continue to focus on the Mann paper, as if nothing else has happened since. This is a political decision, not a scientific one.

    The next and most interesting question would be how the NY Times reporters decided upon this emphasis. Is this from a press release from the contrarians? Will they please explain themselves?”

    My reading of this piece is that they were explaining the background of the controversy over Mann et al, and the flap caused by Barton some months ago when he began to harass some government-employed climatologists.

    It’s perfectly reasonable, in fact necessary, for the Times to report this background material. The NAS report was commissioned because of Barton’s committee’s actions. Commissioned by another committee whose Republican chair’s tired of Barton an Inhoue’s (is there any polite way of saying this?) lies.

  48. 48
    Eric Swanson says:

    RE: #46

    John L. McCormick wrote:

    “In these ten years China and India will continue investing in conventional power generation equipment and vehicles. There is nothing else commercially available to steer the growth projection down….and to those quick to offer solar panels, wind turbines, hybrid vehicles as their alternative to the India-China markets, I say bring back the purchase orders and I’ll listen to your challenge of my pessimistic view….”

    Here’s a recent comment about China’s development.
    Jun. 10, 2006 – Philadelphia Inquirer

    China’s going solar
    By Tim Johnson

    Thriving firms that manufacture low-priced solar water heaters have helped build the world’s largest market for the rooftop devices.

    Between 30 million and 40 million families have solar water heaters on their rooftops, allowing nearly 200 million people to enjoy hot showers and use warm water to wash clothes and dishes. Explosive growth is forecast for years to come, slightly slowing China’s surging appetite for conventional energy.

    In Shandong province, which juts into the Yellow Sea, and in other rural areas of China, millions of rooftops hold the sloping panels of vacuum-tube heat collectors. The solar collectors cost from $160 to $750 for high-end models. In rural areas, the solar heaters are becoming standard appliances, like gas stoves. Those without them feel left behind.

    The Chinese have embarked on a path using evacuated tube hot water collectors. These are very efficient, much more so than the flat plate collectors built in the 1970′s and 1980′s. As I recall, this idea was known back then, but it was thought to be too expensive to build. But, the Chinese are doing it. How long before Home Depot and Lowes, etc, are selling these? Or maybe your neighborhood Mal-Wart will jump on the band wagon too? We can only hope it’s not too late.

  49. 49

    Re: 45. Now Gar you know darn well that 250 degrees centigrade and raining sulfuric acid may be “very” bad, or maybe “really really” bad, but there is just no way in hell that anything can be “infinitely” bad! That is a scientific impossibility! And you know darned well that sulfuric acid is in woefully short supply in U.S industry, and about half the U.S. Senate will probably get a piece of the action! So I’m not going to argue with you! And I’m definitely not going to argue with Stephen Hawking! Do I look like I want my ass handed to me? You go argue with Stephen Hawking!

  50. 50

    Stephen McIntyre told BBC News that he felt the report had upheld “virtually all of our technical criticisms of MBH and did not reject or refute any direct points that we made.”

    What did those technical criticisms amount to, in terms of altering the key findings of proxy reconstructions of past climate? Not much. The NAS commission backs the key findings of the original study. The report says it has very high confidence that the last few decades of the 20th Century were warmer than any comparable period in the last 400 years, and “plausibly” in the last 1,000 years. The “alarming” part of the hockey stick graph, the sharp upward spike in the late 20th century compared to the last 4 centuries, is vindicated with a high degree of certainty.

    McIntyreâ��s technical criticisms of MBH 98 have provided cover for an avalanche of irresponsible attacks on the credibility of climate scientists themselves. Noisy complaints abound that the “hockey stick is broken”, MBH 98 is “rubbish”, the hockey stick is “religion, not science”, or “politics, not science”, a “scientific fraud”, or merely “alarmist scare tactics” by wild-eyed fanatics bent on extorting lucrative grant funding from government bureaucracies.

    The idea is widespread that attacking the credibility of this graph undermines the scientific foundation of the AGW theory. This report repudiates, once again, this flawed reasoning. But in the minds of the public the hockey stick is about global warming, not arcane statistical technicalities. The scientific credibility of human caused global warming remains intact. The NAS report concludes that the hockey stick graph is credible, legitimate science, not a scientific fraud. That’s why this report is widely seen as a vindication of Mann’s work, and McIntyre’s criticisms are largely inconsequential.

    CO 2 levels are higher than at any time in at least the last 650,000 years. The rate of increase is accelerating; 2005 saw one of the largest increases on record. China is building a new coal fired power plant every week.

    Greenhouse gases warm the planet. Within the next 50 years, global temperatures are likely to be higher than at any time in the last 100,000 years. Unless of course, it’s all an artifact of the “urban heat island”: after all, we are just coming out of the “Little Ice Age”, the satellites show cooling, so the models can’t be trusted, and Mars is warming too, so it must be the sun.

    Call me an alarmist, but I’m going to stick with the vast majority of actual scientists on this one.

Switch to our mobile site