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What we can learn from studying the last millennium (or so)

Filed under: — mike @ 15 May 2010 - (Español)

With all of the emphasis that is often placed on hemispheric or global mean temperature trends during the past millennium, and the context they provide for interpreting modern warming trends, one thing is often lost in the discussion: space matters as much as time. Indeed, it is likely that the regional patterns of past climate changes, rather than simple hemispheric or global mean temperature trends, will best inform our understanding of the dynamical mechanisms involved. Since much of the uncertainty in future projections relates to regional climate change impacts, it makes particular sense to focus on those changes in the past that involve regional changes and the underlying mechanisms behind them.

For instance, melting of the cryosphere (and consequent rises in sea level), subtle shifts in drought and rainfall patterns, and extreme events, are all regional effects that could be important threats to ecosystems and our environment. Such changes are often associated with phenomena like ENSO or the North Atlantic Oscillation. Yet there remain large uncertainties about how such mechanisms will respond to anthropogenic climate change.

There are a number of potential ways forward to improve our understanding. A first step is to look directly at the time-series of specific systems (like the ENSO index or the ocean temperatures in the North Atlantic) and try to extend them as far back as possible using proxy data. This gives more information on what the natural variations in these phenomena look like, and thus a better idea of how big a forced response would need to be before it could be reliably detected. Secondly, we can look to see if there is a relationship between various natural drivers of climate change (volcanic eruptions, solar variability or orbital forcing say) and any characteristics of these phenomena – amplitude, frequency or duration. Do volcanic eruptions appear to affect El Niño for instance?

For phenomena that need annual or decadal resolution data to be resolved, the last millennium or so is an obvious (and only) time period to be looking at for it is only for that period that there is sufficient paleo-data coverage of high enough temporal resolution. Other periods – such as the mid-Holocene 6000 years ago – are also useful, but the results are more long-term in nature (there is also a discussion of the value of different periods for reducing future projection uncertainty in this recent paper).

There are a number of different approaches to looking at reconstructions in recent centuries – some rely on high density regional networks (as seen in this recent paper by Guiot et al concerning European temperature trends for which they mostly used pollen data) and some rely on wider networks of more diverse proxies which aim to capture longer-range correlations to specific phenomena (such as the recent Mann et al (2009) paper).

When this is done, people usually find that while it was relatively cool in global mean temperatures from the 1400s to the 1800s known as the “Little Ice Age” and relatively mild in the 900s to 1300s interval ( sometimes termed the “Medieval Warm Period”). But the spatial reconstructions reveal, however, why such global terms can be quite misleading, and why alternative phrases such as the “Medieval Climate Anomaly” are being increasingly favored by the community. This latter terminology recognizes that while the interval displayed significant climate anomalies, they varied greatly, even in sign, from region to region. Many of the more profound climate anomalies, moreover, involve variables other than temperature, such as drought, rainfall, and atmospheric circulation. Though the medieval period is seen to be modestly warmer globally in comparison with the later centuries of the Little Ice Age (the peak global mean warmth is likely comparable to mid, but not late, 20th century warmth), some key regions appear to have in fact been colder, while other regions appear to have been warmer. Southern Greenland, for example, appears within uncertainties to have been as warm as today. However, much of the tropical Pacific was unusually cold, suggestive of the La Niña phase of the ENSO phenomenon (a similar conclusion was reached by Trouet et al (2009)). Thus even though some locations may have been as warm or warmer than today, the hemispheric mean appears not to have been.

Why does this matter? It matters because there are plenty of factors that can affect the overall mean temperature (solar variability, volcanoes, greenhouse gases, internal variability etc.) and so it is hard, given the uncertainties in the solar or volcanic reconstructions to precisely attribute the paleo changes in the global or hemispheric mean to these factors. But if we can look at more complex fingerprints of the changes, it might be possible to be more quantitative in those attributions since the spatial fingerprints of the different factors are easier to distinguish. Furthermore, if we can clearly tie the regional patterns to the different forcings, we might be able to use that information to inform regional projections under future conditions.

Thus we can basically say that the warmer conditions of the Medieval era were tied to higher solar output and few volcanic eruptions and the cooler conditions of the Little Ice Age resulted from lower solar output and more frequent volcanic eruptions. But these drivers appear to have had an equally important, though more subtle, influence on regional temperature patterns through their impact on climate phenomena such as ENSO and the North Atlantic Oscillation. The modest increase in solar output during Medieval times appears to have favored the tendency for the positive phase of the NAO, associated with a more northerly jet stream over the North Atlantic. This brought relatively greater warmth in winter to the North Atlantic and Eurasia. A tendency toward the opposite negative NAO phase helps to explain the enhanced winter cooling over a large part of Eurasia during the later Little Ice Age period.

There is some model support for these patterns (see also instance Shindell et al, 2001) when the models include interactive ozone photochemistry to produce this dynamical response to solar forcing, but it is not captured in a simulation of the NCAR CSM coupled model which lacks those processes. Neither model simulation reproduces the apparent La Niña pattern seen in the Medieval temperature reconstructions:

Figure 1: Spatial pattern of mean temperature difference between the MCA and LIA periods (defined at the intervals AD 950-1250 CE and 1400-1700 CE respectively) compared with simulations of two different climate models forced with estimated differences in natural (volcanic and solar) radiative forcing between the two periods (Mann et al, 2009).

Other model simulations, however, using a climate model that exhibits a particular tropical Pacific mechanism, do reproduce such a response. In such models, the tropical Pacific counter-intuitively tends to the cold La Niña phase during periods of increased heating, such as provided by the increase in solar output and low volcanism of the Medieval era. If this response holds for the future, something that is still vigorously debated, it could imply a more La Niña-like response in the future. Most of the state-of-the-art climate models, e.g. those used in the IPCC Fourth Assessment, by contrast, suggest the opposite–a more El Niño-like future climate. The credibility of the models with regard to this phenomenon is not high, however, and lots more work is going to be needed (both on paleo-reconstructions and model improvements) before we can be confident in the future projections of changes in ENSO-like dynamics and mean state.

690 Responses to “What we can learn from studying the last millennium (or so)”

  1. 551
    Completely Fed Up says:

    Yes, whatever I say you refuse to read and then complain I’m not saying what I think.

    Then, when I point you to where I’ve said it, go “Whatever, dude”. I suppose that’s easier than reading what you’ve asked me to write and means you can continue to believe yourself in the right.

  2. 552
    Completely Fed Up says:

    “Paleo-climate evidence is much less robust that recent physical observations, due to the many uncertainties involved.”

    It’s a lot less certain that the sensitivity is less than 1 than it is that it’s greater than 2.

    Yet somehow you’re concentrating on the 2.

    I don’t think you’re as worried about the certainties as you’re making out.

    Bah, what am I saying? You’re Max.

  3. 553
    Ray Ladbury says:

    The greenhouse nature of CO2 is a fact–as certain as any scientific fact we have. However, if you look at the various distributions of probability of sensitivity for different lines of evidence, you find that those we understand best provide very little support for a sensitivity below 2–and if they are wrong, we get much more of our distribution going to high sensitivity than to low.

    Now this is a BIG problem, as the consequences of climate change scale roughly exponentially with the temperature change–to the point where for a sensitivity of 5 degrees per doubling risk is effectively unbounded.

    However, I think that the remarkable agreement is actually pretty significant. A quick Bayesian analysis places the probability of getting such agreement around 3 at less than 6.5% if the real sensitivity were below 2–and that’s a conservative estimate. So, in effect, you are betting the future of humanity on at least a 15:1 longshot. Since the alternatives are to go with the best science or to go diametrically against it, I have a hard time seeing how one would justify inaction.

    China is an amazing place. My brief time there left me amazed at how delicately balanced it was–and that was 25 years ago. India is certainly more chaotic, but it also seems more robust

  4. 554
    Jacob Mack says:

    Manacker: the weight of the analysis of data indicates a clustering of 3 degrees increase in global mean temperature with a doubling of C02. It may be higher, but it is very unlikely to be lower and will not only be 1 degree and it is very probable to be above 2 degrees. It may be possible to be just under 3 degrees, but virtually impossible to be 2 degrees and it is impossible to be only 1 – 1.5 degrees.

    Now in reagards to crops Ray made a slight error in his response regarding no increased calories or crop yields. Some regions will have enhanced regional crop yields and regional crop qualities. As we all know once upon a time the poles were once warm with crops. There will most likely be new species of crops as well, some pests some viable for food, some neither.

    I think what Ray meant to say is that overall globally there will most likely be less crop yields / quality overall, which is fair assertion based upon current data. Between worsening droughts, floods, wind pattern shifts etc… many crops will potentially lower in yield and quality while others die.

    The answers to much of these concerns are: changing soil treatment techniques, fertilization techniques, irrigation methods, Biotechnology/ agricultural engineering, desalinization of oceans for potable water supply, and of course reducing overal GHG emissions.

  5. 555
    Jacob Mack says:

    Now on another point: yes the understanding of AGW is based upon physics, but keep in mind guys that paleo climate data is also very important too. Being that Gavin and others study paleo climate extensively and create reconstructions of past climate, there must be good reasons for it.

  6. 556
    Jacob Mack says:

    # 545 Ray, I want to make a little correction to my response to your post on “moat crops.” Somehow I missed that on the first read. I do agree there, but certainly some crops will flourish; not a gamble I want to make, however, under these circumstances.

  7. 557
    Hank Roberts says:

    Max is good at restarting long discursive arguments by rebunking claims and then arguing with people about them.

    If you want to convince the audience, point to actual references, don’t argue with Max. He likes when you argue — he gets to repeat himself.

    Debunk the claims. Point to good sources people can check for themselves.

    (Note: “This graph will stay up to date with the latest year’s values, so feel free to copy the image link to your own site, but please link back to these notes so people can understand it and play with it themselves.”)

  8. 558
    Ray Ladbury says:

    Point well taken. I think people do not realize how dependent we are on a very few crops in terms of producing calories and grams of protein. Nor, when they equate warmer with more productive, do they realize that fetid is not the same as fertile.

    I’ve lived in the tropics in agricultural areas and seen what farmers face. It ain’t pretty.

    I do think that we might be able to mitigate some of the threats–but ironically, the best tools for doing that–the models–are the ones our denialist friends distrust the most.

  9. 559
    Completely Fed Up says:

    #552 missed out &lt’s.

    Should say

    “more likely it;s

    “you’re concentrating on the less than 1 and not on the greater than 2”

  10. 560
    Septic Matthew says:

    513, Ray Ladbury: Third, there is no credible alternative theory. At most there are a patchwork of suggestions that attempt to account for a tiny portion of the evidence (and mostly fail).

    On that I agree with you. There are others who find the solar influence theory to be credible (though incomplete.)

  11. 561
    Jacob Mack says:

    Ray, # 558, completely agreed. When I was a child I lived on a farm with my grandmother, for a number of years in Massachusetts, and later on my family had a several acre garden we tended to as well. Now I live in the agriculture rich town of Hollister CA.

    People seem to forget that hundreds of thousands to millions of years ago we (and many current species of life) were not here on this planet, and so even with different climate conditions in the past survived and even thrived on by various species of animals and plants does not necessarily apply to us humans and our current collective ecosystems.

    I do think that we can do far more to reduce GHG emissions and mitigate future consequences through the methods I already aforementioned. The literature is pretty thick on such matters. I also know that good farmers can do a lot to protect their crops based upon what I have seen, albeit less time than yourself and others here.

    I do not think humanity will do all that it can to actually directly lower GHG emissions, to be perfectly honest, as there is far too many politicans and economic oligarchists too. I know there is a place for politics and economics and they can help provide answers to reducing the net positive impacts of AGW, but right now the state of the system continues to move awat from rational science based and feasible courses of action.

    Now according to the EPA and other sources, over the last several decades we have reduced air pollution by a large percentage and of course we all know that there is not as much acid rain even from when I was in elementary school. However, there are far many other issues and with the population of the globe approaching 7 billion, the probability of reducing GHG emissions anywhere near enough looks ever more bleak.

    This is why mitigation/adaptation is so important to me, atleast. We cannout power the world on wind and solar alone in the current economic climate as well as, regional weather aspects which makes either of these energy sources not viable. Look at Germany with its economic issues as they attempt to build still more solar panels while they continue to take in immigrants without skills or education as highlighted in recent issues of the Economist. The Greece recession and the general European financial crisis also makes it more difficult to fund such applications.

    It is amazing what Biotechnology can now accomplish as well as new agricultural growing techniques. More indoor farming techniques are also not out of the question.

    If I recall corrrectly, Ray, from a post a year or two ago here at RC you are ekptical as I am of over reliance upon nuclear energy. Does memory serve me correct?

  12. 562
    David B. Benson says:

    Max Anacker — Actually the correlation over the last 13 decades with the instrumental record is quite good. As notice the steady upward march of temperatures for the past few decades; no slowdown at all. Finally, also note I make a prediction for the average temperature of the 2010s:
    where the first formula ought to read
    AE(d) = k(lnCO2(d-1) – lnCO2(1870s)) – GTA(1880s)
    and the results are in good agreement with estimates of Charney climate sensitivity. If you want more along these lines read Tol, R.S.J. and A.F. de Vos (1998), ‘A Bayesian Statistical Analysis of the Enhanced Greenhouse Effect’, Climatic Change, 38, 87-112.

  13. 563

    #551 (against my better judgement)–“. . . and means you can continue to believe yourself in the right.”

    It’s not about being wrong or right. It’s about ceasing to waste my time (and everyone else’s on the blog.)

  14. 564
    SecularAnimist says:

    Jacob Mack wrote: “We cannot power the world on wind and solar alone …”

    Yes, we can. We can harvest vastly more energy from wind and solar than the entire world currently uses, with today’s mature technologies that are already being commercially deployed, rapidly and at large scale — not to mention the far more powerful and far less expensive technologies that are already under development.

    Jacob Mack wrote: “It is amazing what Biotechnology can now accomplish …”

    The only significant thing that biotechnology has “accomplished” is to proliferate proprietary strains of crops that have been genetically engineered to resist a particular proprietary toxic herbicide, with the purpose and effect of increasing the use of that toxic herbicide, to the great profit of the corporation that produces it (and also produces the genetically engineered resistant crops).

    It’s interesting that you greatly underestimate the benefits of wind and solar technology, while simultaneously greatly overestimating the benefits of biotechnology. You might wish to consider where you are getting your information about both.

  15. 565
    Doug Bostrom says:

    Secular Animist, Jacob Mack, before y’all launch yet another “it’s all this or nothing” conversation, would you please consider agreeing on a budget of replies in advance?

    Please give the idea some due consideration, then ignore it if you must.

  16. 566
    Jacob Mack says:

    564 Just the usual sources: peer reviewed journals‚ textbooks‚ peers in related disciplines, professors‚ engineers, and agricultural engineers. Now crops are being engineered to resist higher and lower temps‚ pests‚ herbicides, drier conditions, and less nutrient rich soil. High voltage lines can make wind mill generation of electricity more efficient and farther reaching but not global, and it is not being applied on a grand scale yet. Agricultural sciences as II already referenced has made both preliminary discoveries and advances in crop preservation. Now where are your references? I have many more on the way. Solar is a good way to get off the grid and wind a great supplement ‚ but not the full energy supply solution.

  17. 567
    Jacob Mack says:

    Doug sure. I will keep it short on my end.

  18. 568

    max 540: The most recent record has shown us that AGW has slowed down (or actually stopped) for a few years. Is this the start of a new “trend”?

    BPL: How many times have we told you you need 30 years to establish a climate trend?

  19. 569
    Anonymous Coward says:

    Jacob (#561),
    What has immigration or the economic climate to do with emissions reduction? This is hand-wringing. Don’t listen to the politicians’ excuses. The issue is that there is no political will. If there was, emissions could be reduced quickly by picking the low-hanging fruits. On-demand electricity is way too cheap in Germany considering the amount of nuclear and its planned phase-out. So people keep wasting electricity and coal keeps getting burned in massive quantities.
    By the way: recessions actually make it easier, not harder for the governements of fully independent states to fund renewables and such. Europe as a whole qualifies though individual countries don’t. I won’t explain why as it’s way off topic but I’m sure you have heard that it’s generally recommended for governments to spend during recessions (recall the green jobs hype). There’s a reason for that. Blame your politicians if they deem military spending or roads to be priorities, not the economic climate.
    Demand emission cuts now, not vague promises or excuses.

  20. 570
    Jacob Mack says:

    Anomymous Coward, # 569 you are partially correct. I wish it were that simple to demand change in energy use now, but the economic climate affects what policies get passed and when. I will get into more detail on these points in your post as they are definitely worth disucssing, but for now I need to cook dinner for my wife and relax my brain for the night:)

  21. 571
    Completely Fed Up says:

    “BPL: How many times have we told you you need 30 years to establish a climate trend?”

    Every day for 30 years, I reckon…

  22. 572
    Ray Ladbury says:

    Septic Matthew@560,
    Those who champion a solar mechanism are a wonderful example of what I decry–looking only at tiny pieces of the evidence. There is simply no way a solar mechanism can explain simultaneous tropospheric warming and stratospheric cooling. Period. A solar mechanism would require an inordinately high climate sensitivity to explain the temperature record. Same with GCR.

    The fact of the matter is that a well mixed, long-lived greenhouse gas is absolutely essential if we are to understand Earth’s climate. It is essential to explain many of the characteristics we see occurring now. It is only by ignoring this evidence and by special pleading that the denialists can even come close to explaining what is after all only a tiny aspect of the evidence. They simply are not doing science.

    If they want to convince me and other sciences, they have only to come up with an alternative theory that explains the evidence–all of it–equally well or better with equal economy. Until then, they have nothing to offer and are firmly in the anti-science camp.

  23. 573
    manacker says:

    Furry Cat Herder (542)

    The surface (Hadley) as well as satellite (UAH / RSS) temperature records show a slight linear cooling trend of “globally and annually averaged land and sea surface and tropospheric temperature” starting 2001. GISS shows an almost flat warming trend (+0.01C per decade). The average trend of the 4 records is –0.062C per decade or slight cooling.

    The upper ocean temperature as measured by the more reliable Argo system since 2003 also shows a slight cooling since then.

    These have occurred despite record increase in atmospheric CO2 as measured at Mauna Loa.

    This is obviously not a “long term trend”, nor is it a significant cooling trend, but it is what it is: some (such as Josh Willis) have called it a “speed bump” in global warming, others have used other expressions.


  24. 574
    manacker says:


    How many times have we told you you need 30 years to establish a climate trend?

    Can’t tell you “how many times” (but this is immaterial, anyway).

    Actually, 30 years is a “blip”.

    160 years (1850-2009) is probably long enough to represent a “climate trend”.

    9 years is (admittedly) also a “blip” (maybe you would prefer to call it a “mini-blip”).


  25. 575
    Ray Ladbury says:

    OK, per Doug’s admonition, this will be my only statement on nukes, etc.

    There are 4 problems I see with nuclear energy:
    1)nuclear waste–we have no good, long-term solution to this problem. I do think we can greatly ameliorate this problem by recycling waste, while at the same time increasing the lifetime of nuclear fuel–albeit at the expense of increasing proliferation concerns.

    2)Proliferation is, of course, the second problem. It can be ameliorated by selection of the fuel cycle, but it will remain a concern.

    3)Human stupidity–Every major nuclear accident has been precipitated by some ingenious fool who figured a way to cut corners around safeguards. Human stupidity is boundless.

    4)It is a temporary solution at best and a distraction from finding a sustainable solution at worst. We’ve seen how entrenched interests have sabotaged efforts to resolve the current crisis. It is not an experience humanity wants to repeat.

    Having said this, nuclear power may provide some of the energy needed in the interim. It is certainly preferable to burning coal. This point was driven home last year on a trip to Sri Lanka. The island has always met its meager energy needs mainly with hydroelectric power. Now, with the ind of the civil war, it’s economy is again growing rapidly and it needs energy. Ironically, although it has lots of uranium and thorium, it is building a big coal-fired powerplant, which, I think, is a mistake.

    My preferred solutions are, in order:
    4)natural gas

    Leave the coal in the ground–and while we’re at it bury the CEOs of Massey, Exxon and BP with it.

  26. 576
    manacker says:

    Furry Cat Herder

    Whether you download the temperature data from the 4 records and plot it in Excel (as I did) or let “Wood For Trees” do it for you, you get the same result for the first 9 full years of the 21st century (as I indicated earlier).

    BPL tells me this is too short to be a climate trend, which I have agreed all along.

    I think this requires at least a century to be meaningful (while BPL thinks 30 years is long enough), and the entire 160-year Hadley record is probably even a better example of a “climate trend”.

    But opinions vary on that.


  27. 577
    CTG says:

    #568 BPL

    How many times? I think the answer is infinite. After all, it seemed to take an infinity of times telling Max that climate models do not assume constant relative humidity before he eventually conceded the point. Or did he? I’m sure if we prod him enough he would come out and say it again.

    Anyway, we all know that Max is not here in good faith, he is simply here to accumulate bruises that he can show to his fellow deniers. So let’s not disappoint him, eh?

    So, Max, why is Arctic ice melting at an unprecedented rate this year, eh? Is it because we are in the middle of a cooling trend?

  28. 578
    manacker says:

    DB Benson

    Thanks for link to your decadal temp vs CO2 analysis plus forecast for 2010s.

    Will go through it and give you any comments I may have.


  29. 579
    Ray Ladbury says:

    Max, 30 years is not an arbitrary standard. Rather, you can show that you need at least 22-25 years to even determine the sign of the trend, and the additional 8 years to get a good estimate of its magnitude. Tamino has looked at this.

  30. 580
    manacker says:

    CTG (576) wrote:

    So, Max, why is Arctic ice melting at an unprecedented rate this year, eh? Is it because we are in the middle of a cooling trend?

    Probably the same reason that Antarctic sea ice is growing (changes in ocean currents, wind patterns, etc.?).


  31. 581
    manacker says:


    You asked me (576) “why is Arctic ice melting at an unprecedented rate this year, eh?”.

    Suggest you check the record:

    The last month, for which data are published, is April. The NSIDC record shows (extent in msk):
    15.00 (1979-2000 average = baseline)
    14.58 2009
    14.69 2010

    April 2010 is 2% below the baseline average (1979-2000).
    April 2010 is 1% higher than April 2009.

    I do not see “an unprecedented rate” here, CTG Do you?

    By contrast, the extent in April 2007 was at a low point of 13.88 msk, so the sea ice has recovered by about 6% since then.



  32. 582
    Hank Roberts says:

    > Manacker
    Find a more reliable source, don’t just assert belief; help the reader.

  33. 583

    Manaker @ 573 and 575:

    Well … yeah, and that’s a collection of points I’ve been making for a while. If you click on my name you’ll get a thing I posted on Facebook a bit more than 2 years ago because I felt that I needed to be able to say “See, I told you so!” to the folks who insist that the Sun plays no role in climate.

    But as I point out in that post, this “respite” or “speed bump” is a temporary thing and we need to exploit the hell out of it and shift to renewables, and away from carbon-based fuels, as fast as we possibly can.

    If we assume that SC24 is going to be a 14 or 15 year cycle, that’s what we’ve got to act — about another 10 to 12 years. We can’t rely on SC25 being another fizzle — we have to assume that SC25 is closer to average and if we’ve not gotten a handle on CO2 emissions that the 20’s and 30’s are going to be HOT.

    As for Ray and the other “The sun didn’t do it!” crowd, “Solar cycles play a role” does explain the current sideways trend, as well as the temperatures during the Dalton and Maunder minima. Deal with it.

    — Julie.

  34. 584
    Completely Fed Up says:

    Max #573, there is no cooling trend in the Hadley or GISS dataset since 2001.

  35. 585
    Completely Fed Up says:

    “I wish it were that simple to demand change in energy use now,”

    It’s easy: demand energy change now.

    Use less.

    Use the clothesline to dry your clothes.

    Go shopping three times a week and walk it.

    Waste less.

    There’s no time lag on that.

  36. 586
    Jacob Mack says:

    584 CFU all good points. As a matter of choice we gave up the car 2 years ago, I walk everywhere in town, including all grocery shopping, we do not use a washer and dryer at home, we use heat only for one when needed, we recycle, and use only energy efficient appliances. My former post to AC referred to my desire to see more green tech implemented here.

  37. 587
    Jacob Mack says:

    Ray 574 fair enough. I agree on all points except I Iike natural gas better than nuclear due to the disposal issues you mentioned.

  38. 588
    CTG says:

    #580 Max the eternal optimist…

    Of course, it is now nearly the end of May, so in a couple of days time you will be able to post the May figures. You might want to reconsider your words then, as the 2010 is now not only well below the 2SD range, but is tracking well below the 2007 line.

    As with most of the things you say, you are out of date, Max.

  39. 589
    CTG says:

    Note how Max is careful to choose his timframes: “the first 9 full years of the 21st century” is referring to this, which does indeed show three trends going down, and one going up.

    But why leave out the first fourth months of this year, Max? Oh that’s why. UAH is now heading up. How inconvenient of it.

    And if the trends are sensitive to the end date, are they also sensitive to the start date? Oops, looks like they are.

    But maybe that’s unfair, as that’s a longer timeframe than Max’s 2001-2009, so let’s restrict it to 2000-2008. Oh dear.

    You see, Max, when trends like these are so sensitive to start and end dates, it should be telling you something – specifically, it should tell you that you are using too short a window. None of the trends I have plotted so far – up or down – are particularly relevant to deciding whether it is warming or not, as they are not long enough to remove the internal variability.

    As has been pointed out to you on many, many occasions, you need 30 years to determine trends.

    Is there the remotest possibility that you are going to listen this time, Max, or are you going to be back in a couple of weeks spouting the same old nonsense?

  40. 590
    manacker says:

    Hank Roberts

    You advise me to “find a more reliable source” for 21st century temperature data.

    I went to the source of the data (Hadley, GISS, UAH and RSS published records), which I then plotted in Excerl. Then I checked the “Wood for Trees” rehash (which agrees with my Excel curve).

    I recking the root source of the data is a more reliable source that your cited “rehash” article. Don’t you?


  41. 591
    Hank Roberts says:

    People need to find a more reliable source than Max. He’s an expert at keeping any digression going so long as comments feature his name. Eschew.

    Want facts about science? I recommend Robert Grumbine.

  42. 592
    manacker says:


    You wrote (584):

    Max #573, there is no cooling trend in the Hadley or GISS dataset since 2001.

    The annual records for 2001 through 2009 show:

    You are correct for GISS, which shows a warming trend of +0.01C per decade.

    You are wrong for Hadley, which shows a cooling trend of -0.06C per decade.

    Both satellite records (UAH and RSS) also show cooling trends.

    Check the records out for yourself.


  43. 593
    manacker says:

    Ray Ladbury (579)
    CTG (589)

    Regardless of what you have both posted, 30 years is an arbitrary period for determining climate change (probably too short).

    The IPCC “poster period” (AR4 WG1) is from 1976 to 2005, a period in which CO2 emissions were growing at 0.4% compounded annual growth rate (and there is a good CO2 / temperature correlation).

    The statistically indistinguishable period 1910-1944 occurred before there was as much increase in CO2.

    Another similar period occurred in the late 19th century, when there was almost no CO2 increase.

    In between there were slight cooling periods (also of about 30 years length).

    If one believes that a 30-year cycle can be used for determining “climate change”, then one should look at all these 30-year oscillations and their causes, and find an explanation for the fact that some of these observed cycles show no statistical correlation with observed changes in atmospheric CO2

    If one prefers the longer-term look, one should look at the entire 160-year period of warming. That would be my advice.


  44. 594
    manacker says:


    You may not be aware of this (many people are not), but the 21st century started New Year’s Eve 2000/2001 (and 2001 is the first year in the 21st century).

    So I have shown the records for the first 9 full years of the 21st century.

    This will not change much by “splicing on” the first four months of 2010.

    One can also “cherry-pick” the starting date as 1998, which shows a different trend, but still confirms that the past few years have been flat to slightly cooling.

    Arbitrarily “cherry picking” the last year of the 20th century and adding it on (as you have done) is simply an exercise in “sticking one’s head in the sand” to deny the fact that it has been cooling slightly since the 21st century started.

    I am not claiming that this is a “trend”. Kevin Trenberth called it a “travesty”, but I would simply call it a “blip”.

    [Response: That’s not what Trenberth was referring to, and you are ignoring the steady increase in upper ocean heat content–jim]

    Can you understand this?


  45. 595

    Max 573: The surface (Hadley) as well as satellite (UAH / RSS) temperature records show a slight linear cooling trend of “globally and annually averaged land and sea surface and tropospheric temperature” starting 2001.

    BPL: No, they do not. And you still don’t appear to understand what a “trend” means. It’s not “a direction in the curve of arbitrary length.” A “trend” has to be statistically significant.

  46. 596

    max 574: 160 years (1850-2009) is probably long enough to represent a “climate trend”.

    Super. Hadley CRU mean global annual dT regressed on year gives

    dT = -8.625 + 0.004382 Year + ε

    with t statistics of -16.43 and 16.11 on the intercept and Year term coefficient, respectively–a positive trend significant at p < 4.38 x 10-35. 62% of variance is accounted for. N = 159.

  47. 597

    max 576: I think this requires at least a century to be meaningful (while BPL thinks 30 years is long enough), and the entire 160-year Hadley record is probably even a better example of a “climate trend”.
    But opinions vary on that.

    BPL: No. “Opinions” are irrelevant. Statistical significance is something that can be measured.

    You need to take an introductory statistics course before you try to debate this issue. You just don’t know the basics.

  48. 598

    Julie 583,

    TSI or Sunspot number accounts for no more than 2.5% of the variance of dT 1880-2008. Deal with it.

  49. 599
    manacker says:


    I personally agree that you are spot on with the impact of SC24. Whether SC25 will be another fizzle is anyone’s guess, and I know there are opinions out there that this will be the case (which I am sure you have seen).

    The “respite” (or “speed bump”) may be a temporary thing, or it may be the start of a 30-year cycle of slight cooling before a warming cycle again takes over (as has happened in the past).

    I also agree that trying to myopically tie everything to human CO2 while ignoring natural forcing, such as occurred during the Dalton and Maunder minima, for example, is simply a form of denial.

    My point in all this is simply that there is still a whole lot that we do not fully understand about what makes our climate do what it does and (as a result) what the quantitative impact of increased CO2 concentrations will really be.

    You may be right that once fizzling solar cycles stop we may be in for a significant warming oscillation, putting us back on the long-term underlying warming trend of 0.04 to 0.05C per decade. Or the long-term trend line may shift upward to something like 0.1C or even 0.2C per decade. But, despite all the model simulations, etc., it’s still anyone’s guess what will happen.


  50. 600
    manacker says:

    Jacob Mack
    Ray Ladbury

    Natural gas is a good clean source of energy and can easily be used for motor vehicles. Recent estimates tell us that there are enormous sources in shale, assuring a supply for well over 100 years, even at accelerated consumption rates.

    Nuclear fission has the disposal problem, which Ray mentioned, but new thorium-based fat breeder technology may go a long way to solve this problem. There is no real long-term shortage of fuel for nuclear fission.

    The other problem is that spent fuel can be converted to military use, so it would not make sense for every politically unstable nation to have nuclear power.

    Nuclear fusion is also a future possibility. My personal prediction is that it will become a reality before cost-competitive wind or solar power does (except for isolated small uses), due to the inherent unreliability (or limited on-line factor) of both wind and sun.

    I also believe that “Ol’ King Coal” will be around for a long time to come, as these lower CO2 alternates become reality.