The apparently simple question like the one in the title of this essay is in fact almost impossible to answer unless it is specified further. Even then, it has been argued that that it implies a quantity — average global temperature — that is both mathematically and thermodynamically impossible to calculate. Interested readers should go to the link to explore further, but a short-cut is that it is as sensible as referring to the ‘average exchange rate’ of all currencies in the world today, or the average of all the telephone numbers in the telephone directory.

Perhaps a prior question is: what is the optimum temperature for human beings and human societies? The assumption underlying the notion of ‘catastrophic’ anthropogenic global warming, after all, is that we are moving away from some kind of optimum towards something dangerous. What is that optimum? It can’t be the period before the Industrial revolution, because that was icily unpleasant, as Judith Curry and others have pointed out. Given the contribution that more carbon dioxide makes to the lives of plants, and therefore animals, I can’t see why another degree or so would be other than beneficial.

But, as I have said before, if one wants to talk about the global warming or ‘climate change’ issue, there is no help for it: one has to use the data that we have. And they are not much help, either, because another prior question is:  ‘Warming or not — from when to when?’. Over the last half-million years? The graph looks like this.



The present is to the right. On this ice-core evidence (Antarctic) previous interglacials were warmer. You don’t like that — too long ago? What about the time since our own interglacial began? The graph looks like this.


Yes, more ice cores, from one place. Alas, that’s all we really have. You’ll notice that the modern period is of much the same warmth as some earlier periods, but not as much as that of the Holocene Optimum. So are we warming? On the evidence of that graph, we seem to go through warm and cold periods, and maybe the long-term trend is a cooling one. Don’t like that? Let’s get to our own present and recent past. Here’s a graph I used a little time ago. It doesn’t go quite to the present.


My grandparents, whom I remember quite well, were born in the 1880s, so this whole period is relevant to me. What I take from this graph is more warm and cool phases, though of shorter duration that in the previous graph. There were rising warmth periods, of about the same duration and trend, from 1910 to 1940, and from about 1975 to 2000. There were cooling periods from 1880 to 1910, and from 1940 to 1975. There has been a relatively flat period from 2000 to the present, though this graph only shows the first part of it.

What are we to make of all this? Let’s leave carbon dioxide out of it for a moment. The three graphs show that the planet goes through phases of warming and cooling. There are long phases, medium phases and short phases. We seem to be in a short cooling or static phase at the moment, compared to earlier periods. This period will get cooler or warmer in due course. There are many candidate explanations for why all this happens and has happened, and we can leave them out for the the moment, too.

But what seems almost indisputable to me is that there hasn’t been some kind of special ‘right’ climate for humans. Our species has had to cope with more and less warmth, as we do at the moment. We haven’t had to deal with a really cold period since the 17th and early 18th centuries, but we will be much better prepared for the next one. If we go into a new warming phase, we’ll cope with that too. Eight years ago, in my ‘Cool Look’ address to the Australian Planning Institute, I said I was prepared to accept  the IPCC’s estimated average increase in temperature over the 20th century of 0.60 plus or minus 0.20C. I still am. Is it a problem? Not on the evidence of the graphs.

Is it unprecedented? That was the next issue — the orthodox position is that the warming of our period is unprecedented in human history (and must therefore be our fault). I repeat here a little of what I wrote then.

By 10,000 years ago the first small permanent settlements began to appear, as people assembled and domesticated animals, learned how to plant crops, and abandoned being hunter-gatherers. There were then, according to some estimates, about a million of our ancestors. It seems to me to be no coincidence at all that global temperatures had begun to level out. The evidence for these temperatures is based on Greenland and Antarctic ice-core data, and I need to say at once that what happened in Greenland or the South Polar regions may not have happened anywhere else. Average temperatures seem to have remained within a narrow band of about two to three degrees Celsius ever since, save on a few occasions, such as the Mediaeval Warm Period, when English monasteries grew grapes and made wine, and the later ‘Little Ice Age’, when the Thames froze in 1683 and a Frost Fair continued for two months on the ice. On the evidence, present average temperatures are similar to those in the first century AD. 

On the face of it, there is nothing especially unprecedented about the 20th century temperature rise, given its ‘agreed’ size. Shifts up and down of that magnitude and more seem to have occurred in the past, and will presumably occur in the future. Climate change is not new, and occurs for reasons that can have nothing to do with us. Orbital changes, sunspots, volcanic eruptions and meteorites have effects on the earth’s climate, and these causes are external to us. We simply have to put up with the changes and adapt what we do to them. Whatever warming that is happening now, and whatever contribution we humans are making to it, have to be seen in that context.

Eight years have passed, a great deal more research has been done, and the science is still not at all settled. I’ll stick to what I wrote then.

Next: Are we causing the warming?

Further reading: I wrote an essay on what had happened since 2008 six years later, and you can see that here. The website has lots of pieces about warming and measurement, because it remains a central intellectual interest  for me. My basic position is that what we have as data is just awful, and no basis for making public policy. But elected governments, responding to insistent cries of approaching doom from the Greens and their sympathisers, desperately search for data, any data, that would allow them to make good policy. I don’t believe such data exist, and that governments should do nothing. Alas, that is not a position that governments like at all — they will be accused of indolence or worse. So we have to discuss the data we have. Hence this essay, and others like it.


Join the discussion 103 Comments

  • Neville says:

    The Concordia Uni study shows just 0.7 C of warming since 1800 and OZ’s contribution is an unmeasurable 0.006C since that time. Big deal.
    Of course the Lloyd study found that the average deviation in temp per century over the last 8,000 years ( 80 centuries) was about one degree C. So where’s the impact from increased co2 levels? Here’s the Lloyd study using both Greenland and Antarctic ice cores———–

    But can urgers please tell us how to mitigate their so called CAGW?

    • David says:

      ‘But can urgers please tell us how to mitigate their so called CAGW?.”

      1. Increased investment in R&D to develop alternative energy technologies.
      2. Introduce a carbon tax/subsidy to integrate these new technologies into the economy
      3. Invest in University of Third Age to help all the old people understand the underlying science behind CAGW
      4. Offer free Jungian psychoanalysis to help recalcitrants workshop their fears.

      • Neville says:

        David you couldn’t answer my question. Your joke file above is good for a laugh but couldn’t reduce co2 levels that would provide any measurable different to temp at all. Have you read the latest Royal Society NAS report?

  • Neville says:

    My first comment is in moderation again.

  • Mike says:

    Don your first figure shows a temperature range or should I say anomaly from -10 to about 3. Something I sometimes think about is that humans survived that, humans existed throughout that entire period. We adapted as all animals or life for that matter does. There is a pretense in the environmentalist world that nothing can survive the smallest change in anything. Is it ignorance or malicious fear mongering?

    I am in Canberra at the moment current temperature 14.2°. Suppose I head over to the airport and take a plane to Darwin I have to suppose that is a very quick plane but the temperature in Darwin at the moment is 27.9°. This is a change of 13.7° vastly beyond anything the most extreme fear mongering crowd can imagine. Humans live in Siberia where it can be -40° we survive Antarctica where it can be -80°. In the other direction lots of people live in the tropics and even areas in the world where it is over 50°.

    If you ask what is the temperature they would like you get no answer. We are supposed to spend vast amounts of money so that changes of less than a degree can be avoided. If it is to be believed they are honest and genuine in this I think they are very good candidates for a mental asylum. I think there is another agenda which I will not expand on but I consider this movement to be absolute enemies of civilisation.

    • Alan Gould says:

      On that ‘What temperature would you like?’ I have this vague item of information bobbing about in my mental fluids. A study was done (I do not recall its name, date or authorship) to find the ideal climatic location on the earth (I have no idea of the criteria for that ‘ideal’) but the finding I do recall clearly. It was Port Macquarie NSW.

      • Neville says:

        Not a bad spot PM, you could certainly find a lot worse.

      • Mike says:

        Perhaps Port Macquarie should become the gold standard of the ideal climate. I know people who have left Canberra in order to go and live there so perhaps they were onto something.

  • Neville says:

    Over at climate audit Steve McIntyre has recently obtained more data on some of the past studies that claimed to show less warming for the Med WP. Using his maths and stats skills he has been able to find much higher dendro info for the Med wp when compared to recent warming.
    Some of his graphs show the results compared to the earlier studies and Willis Eschenbach’s comments backed up by maths expert Nic Lewis endorse Steve’s results. Here’s Willis’s comment———-

    “Steve, I’m overjoyed to see your continued deconstruction and disambiguation of the tree ring data.

    I was saddened but not at all surprised by this statement:

    Although the article in consideration was published more than a decade ago, the analysis in today’s article was impossible until relatively recently, because coauthor Luckman withheld the relevant data for over a decade.

    The tragedy of modern climate science is that this kind of scandalous scientific malfeasance goes not only entirely unpunished, but is completely ignored by the overwhelming majority of mainstream climate scientists. Gotta say, it angrifies my blood. People tell me all the time that I’m too passionate about this kind of scientifically criminal behavior.

    The taxpaying public funds these charming fellows to go adventure in the wild and secure important scientific data, and they treat it as if it were their own. Disgraceful and shameful. Me too passionate? I say that people are not passionate enough about this underhanded, deceptive withholding of scientific information.

    Except Canadians, I have it on good authority that they never sweat unless there’s emotional attachment. But for the rest … where is the richly deserved outrage?

    But I digress. Good stuff, and fascinating. I gotta learn more about “random effects statistical techniques”, where might I start my further education?

    My best to you,

    w.” End of quote.

    Some of these people seem to be extreme cherry pickers and con merchants, certainly not serious scientists.

    • Mike says:

      Seems to me if you manage to discount the mediaeval warm period you then have to discount all warmer periods in the current interglacial. There is the Roman the Minoan and other unnamed ones before that, you can see these in Don’s first graph. Perhaps those who try to discount the MWP don’t realise that there were warmer periods in the past? I suppose we will see an effort to discount all ice core studies.

      • Mike says:

        Just looking at this again you would also have have to discount all warm periods over the past 400,000 years.

      • Junie says:

        Nobody wants it to be true so some people diismss the idea emotionally.Those against usually cite natural variations are causing the earth to warm up. Many of these favor solar variations; however the sun hasn’t varied that much. Satellites have measured the sun’s output very accurately for the last 3 solar cycles (approximately in 11 years in length). The net change is too small to measure. Scientists know a lot of natural variations but none of them can produce the current pattern of warming.If you want to see all the arguments, and why the errors, distortions, confusions and lies behind them, go to skeptical science.

  • Neville says:

    Let’s look at how humans have endured the last 216 years. The planet’s human pop first reached one billion in 1800 and about 2 bn by 1900. Today the human pop is 7bn plus and the first world has an obesity problem, because of our much easier lifestyles and much higher standards of living.
    But according to Dr Goklany’s work and the Lomborg group, deaths from extreme events have dropped by 97% since the 1920s. This huge decrease in deaths from extreme events is despite the fact that many more people are at risk today than in earlier times. So once again, where is the impact from more co2 emissions?
    This is contrary to the nonsense fed to us by the MSM, stupid pollies and delusional scientists. Goklany has worked for the US govt for years and the IPCC and the Lomborg group has at least 4 Nobel laureates among their group and like Bjorn they are experts in stats , maths etc.

  • Neville says:

    Another lesson on how not to measure their so called CAGW, with photos. What a joke.

  • Karen says:

    Hi Don The ideal temperature for humans is 18 degrees to 25 degrees centigrade. Funnily enough, the temperature of the earth for the first 20 feet or so is 18 degrees to 20 degrees. That is the temperature we need to aim for if we expect people to act decently towards each other and the environment. At the moment we are not able to manipulate the weather at will. Strange considering all the other technological skills which we have at our disposal. So best plan, live at ground level if not a bit below it away from rising sea levels. Karen

    • Don Aitkin says:


      Two questions: What is your source for the statement about the ideal temperature for humans? And have the billions of people who live in the tropics been told?

      • David says:

        This reference describes the tropics as having temperatures between 20 to 30 degrees. So I think Karen’s upper bound of 25 degrees (i.e. (20 + 30) /2] looks spot on.

        • Don Aitkin says:

          Still would like the source of this assertion. And 25 degrees is not 30 degrees. And Darwin has many many days with temperature higher than 30.

          • Don Aitkin says:

            Darwin’s long-term AVERAGE is 31.4 degrees C.

          • David says:

            Interesting topic. Here is a similar reference. I found one reference that reported Darwin’s average daily maximum is 32 and its average daily minimum is about 23, so that is a mean of 27.5.


          • dlb says:

            I think we have been in this territory before with that French discussion paper and the merits of average temperatures. The length of time the temperature sits at uncomfortable levels is more important than the yearly or daily average.

            I have often wondered whether the great advances in thinking in Europe over the last few centuries has something to do with people couped up indoors over winter with time to contemplate. Now with the advent of air-conditioning will commerce, arts and science flourish in the tropics? I include places like Darwin and Townsville which may now have their day in, or should I say out of the sun.

    • Neville says:

      Karen I presume you think that people in the tropics don’t behave decently to each other and the environment?
      Why do you think it strange that we’re not able to control the weather?

      • Dalibor says:

        Hi Jonathan,It can be confusing the nbemur of claims being made that the world is warming / isn’t warming and that’s because the issue has become somewhat divided, often for partisan reasons.No doubt what you’ve been taught in school is correct. If a school were to knowingly misteach it’s pupils then it faces prosecution. Global warming has actually been on trial several times in courts of law and on every occasion the Judge has ruled that the facts and science behind global warming are accurate.Those who don’t accept global warming is happening don’t have an argument against the theory. Instead they have used more than 100 different excuses ranging from claims that the world is cooling, that Margaret Thatcher invented global warming, that it’s because Earth is moving closer to the Sun – all manner of unrelated claims.In your question you mention that you’ve learned that a lot of people are against the idea of global warming. In reality there’s not that many. It’s broadly accepted the world over, the only notable exception being the US where it is more of a political issue than a scientific one.If you look at global warming scientifically then there’s no question that it’s happening. No doubt you were taught that greenhouse gases retain heat in the atmosphere and that the more of them there are the more heat is retained. What you may not have been taught is the mechanism by which these gases retain heat, this is something that is governed by the laws of quantum mechanics.You may think that it would be pointless to try and argue against the theory of gravity, and you’d be right to do so. But it’s even more pointless to argue against the laws of quantum mechanics. Not only are these laws universal and invariable, but they’re the most powerful and successful of all scientific laws. Trying to argue against them really is futile – not that it doesn’t stop some people claiming there’s no such thing as global warming.Because the science is so solid, it’s no surprise then that there isn’t a single scientific organisation on the planet that disputes the theory of manmade global warming.So instead, what we’re left with are a nbemur of uncoordinated, unscientific, and largely uninformed individuals who, often for personal reasons, object to the notion that the world is warming and we, as humans, are having a hand in it.It’s very telling that those who argue against the theory NEVER address the issue as a whole, instead they focus on the minutiae and on the distortion of reality. By adopting this technique it’s possible to ‘disprove’ anything. Take gravity for example, if it existed then trees would grow downwards not upwards, water could never evaporate, birds and planes would crash to the ground, the atmosphere would be sucked down to Earth not up in the sky, Earth would compress itself into a tiny ball etc etc.This is an example of the style of argument used by those who reject the theory of global warming. They latch on to an illogical argument and run with it, steadfastly refusing to acknowledge their own ignorance and basically doing everything they can to avoid exposure to anything that opposes their fallacy.

    • Mike says:

      According to the BOM Darwin has a mean low yearly average of 23.2 and mean high yearly average of 32.

  • David says:

    “Depth psychology disorder & climate change” / editor, Jonathan Paul Marshall ;

    “We all know the facts and the disputes about the facts of Climate Change, but what do we understand about the psychology of our response to this potential disorder? In this book, nineteen writers explore our reactions largely, but not only, from the perspectives of Jungian Depth Psychology. Topics covered include the relationship between myth and climate change; nature and psychology; the dynamics of prophecy, poetry and science; western and non-western philosophies; nature and gender; nature and technology; the problems with our common beliefs and ways of thinking about disorder and more. Interludes of stories and poems add to the variety of approaches, and perspectives. This exciting and timely book provides insights into the conscious and unconscious psychology of climate change and disorder. Its original and thought provoking essays aim to help us relate to the Earth from an enlarged and enlivened perspective”

    I think this book looks interesting. I am going to buy a copy.

    • JimboR says:

      Very interesting. I hope you’ll post a review when you’ve read it.

      • David says:

        You could do some interesting stuff. Like develop a model where Myers Briggs sub-scores were used to predict a person’s subjective estimate of the equilibrium climate sensitivity (ECS). I am willing to bet the model would have a respectable R-squared.

        • dlb says:

          So David, what is your hypothesis?
          That the intuitive – feeling types are more likely to go for extreme climate sensitivities?

      • JimboR says:

        I’m more interested in why so many people think they can play climate scientist. If you asked me for an ECS estimate I’d simply refer you to someone who works in the field.

        • Don Aitkin says:

          No one is playing climate scientist. Rather, sceptics wonder at the validity of the argument, given that it is the basis of carbon taxes, ETSs and the belief that we must keep increases to less than 2.0 degrees C above some baseline figure — when none of this can be shown in any accessible and persuasive way.

          ECS is just the current example. It exists because without it there is no AGW scare. But no one find it, those who search provide estimates that are all over the place, and the null hypothesis, surely, is that it is 0.

          Why are you so sure that it exists?

          • David says:

            Don this exchange with JimboR is quite entertaining. But you are not going to be able to wordsmith the ECS down to your preferred estimate. On a graph you provided some months ago the lowest ECS estimate was 16.7 (?) and most were above 2.


          • Don Aitkin says:


            I did warn you about relying on Wikipedia for anything about global warming!

          • JimboR says:

            David, let me summarise the state of play as I see it. Aitkin’s Constant (1.1) is not an ECS estimate. It kinda’ looks like one and kinda’ smells like one, but Don doesn’t believe in ECS so it can’t be one. Because it isn’t one, it doesn’t make sense to test it against any of the PDFs found in the ECS literature. As you point out, if you did (which you shouldn’t) you’d find it a very unlikely candidate value (possibly further evidence that it’s not an ECS estimate). There’s a possibility that the 0.1 component of Aitkin’s Constant is a respectful nod to those who do believe in ECS, but I’m not clear on that so don’t quote me.

        • JimboR says:

          Me? I don’t think I’ve expressed any views on the existence or value of ECS have I? I can’t understand why anyone would care what my views on ECS are; you might as well ask me where’s the best location for a corneal incision. it’s not my field. I refer all such enquiries to those working in the field.

          • Don Aitkin says:

            But that’s what I did. Lewis and Curry — now they’re working in the field. They say it’s low. So do 13 other peer-reviewed papers. Why don’t you take notice of them?

          • JimboR says:

            I do. But when those working in the field come to different conclusions, I don’t feel qualified to choose. I’m happy to let them get on with their work in the expectation that the best theory wins, whatever it may be. I’m certainly not going to pick one or another based on ideology, but I think many in the blogosphere do. I’m hoping David’s psych book may shed some light on that phenomenon.

            I’m told ophthalmic surgeons differ on the best location for corneal incisions too. I don’t plan contributing to that research either.

          • JimboR says:

            Actually, if I remember correctly, your ECS “guess” was one that Lewis and Curry’s paper deemed very unlikely.

          • JimboR says:

            I just reviewed that earlier thread. One thing pretty much all of those 13 peer-reviewed papers agree on on Don, is that your ECS “guess” is very unlikely. So “Why don’t you take notice of them?” right back at ya’.

            “It (ECS) exists because without it there is no AGW scare.”

            Don, that might be why you think it exists, but the people working in the field think it exists because their theories predict it should.

            “But no one (can) find it”

            The same could be said of gravity waves up until last September. and they were first theoretically proposed in 1916. Don what are your views on theoretical physics? Do you consider it a total waste of time?

          • Don Aitkin says:

            Jimbo, with reference to your remark about my ‘guess’.

            I don’t have a guess. What I said was that the null hypothesis surely should be zero. Different thing altogether. You need to read more carefully.

          • JimboR says:

            I was referring back to your 1.1 claim in the comments of this old thread:

          • Don Aitkin says:

            Jimbo, you are confusing ECS with a doubling of CO2. What I wrote in the essay you referred to went like this:

            ‘ I raised climate sensitivity because unless it exists in the real world and unless it is high, then doubling CO2 will produce an increase of around 1.1 degrees C, which is not a worry, given that the doubling takes place in a logarithmic fashion, and there has been very little warming over the last twenty years.’

            I have not said that my guess is an ECS of 1.1. That is something else again. Indeed I haven’t made any estimate at all. What I have said ( many times) are versions of what is quoted above: I’ll stick to a doubling of CO2 causing an increase in temperature of about 1.1 degrees C unless someone can show me very good reasons why (i) there is an ECS, and (ii) it is high. Most of the recent estimates are in lower section of the ICC’s range. They offer me no cause for alarm, or for having a carbon tax, or an ETS.

          • JimboR says:

            I guess I got confused by this exchange:

            “Don, how do you justify an ECS of around 1.1? According to various comprehensive studies the probability of an ECS of less than or equal to 1.1 is very low.” said bobo December 4, 2015 at 4:18 am

            “How do I justify it? Because the tendency of studies of ECS is that the more recent ones point to low sensitivity:” replied Don December 5, 2015 at 6:56 am

          • Don Aitkin says:

            I guess you made the same mistake as Bobo. So let me repeat it all: ECS has not been found; the IPCC offers a wide range, even after thirty years of work (now an even wider range); current papers suggest a low figure; I see no reason yet to accept any figure, and the lower estimates should cause no one any alarm; a doubling from 280 ppm (the estimate for 1780) to 560 ppm is a long way off; there are plainly other factors at work; why bother with ECS.

            Perhaps all three of you could suggest why we should bother.

          • JimboR says:

            Well, regardless of what we call your 1.1 (maybe Aitkin’s Constant?) can you explain how you derived it please. Ideally with an equation, you know… an “=” in the middle, a bunch of maths to the left of it, and 1.1 to the right of it, like real scientists do.

          • Don Aitkin says:

            Jimbo, you always want me to do your work. Let me just quote Stefan Ramstorf, in the Wikipedia article on ECS and its counterpart. I am only interested in the beginning, and you can take it from there. He says it’s easily calculated and without real challenge.

            “Without any feedbacks, a doubling of CO2 (which amounts to a forcing of 3.7 W/m2) would result in 1 °C global warming, which is easy to calculate and is undisputed. The remaining uncertainty is due entirely to feedbacks in the system, namely, the water vapor feedback, the ice-albedo feedback, the cloud feedback, and the lapse rate feedback”;[12] addition of these feedbacks leads to a value of the sensitivity to CO2 doubling of approximately 3 °C ± 1.5 °C, which corresponds to a value of ? of 0.8 K/(W/m2).

            Wikipedia is more convinced of the effects of the feedbacks than I am, but then Wikipedia is a believer.

          • JimboR says:

            Don, 1.1 is your constant, you’re the only one who can explain how you arrived at it. Or are you saying now it was a typo and you meant 1.0?

          • Don Aitkin says:

            Sorry, Jimbo, you have to do your own work. If you search about the consequences of doubling CIO2 you’ll find a variety of estimates; 1.0 or 1.1 degrees C are common ones. I’m happy with either. If you don’t like them, you explain why.

          • Don Aitkin says:

            Oh dear — that was a typo: ‘CO2’.

        • dlb says:

          Its a bit like gambling, the climate is so uncertain that some guess from left field has almost as much credence as expert opinion.

    • bobo says:

      Hi David,

      There’s a free online course entitled “Introduction to Applied Bayesian Statistics for Climate Research” at which might be of interest to you (or anyone else) for making progress on that problem you were thinking about.

      I’ve enrolled and am looking forward to finding a bit of time to go through the material.

      • David says:

        Thanks bobo I will check it out.

        • Serkan says:

          There is the “slight” change in the prgoarm. It’s actually not global warming anymore, since earth is cooling down since 2005 it’s now called climate change instead. There is also the slight misshap of the temperatures rising a few years prior to the rise in the levels of CO2.I’m not going to go into details on a high school question but you might want to look into climate gate (it’s true, the mails presented by what is American party in the US was taken out of context but I’ve read the mails decided fo myself and the pro-climate change propaganda is based on B.S. and even the ones spreading it know it) and you might have a look at articles google-schollar finds.IMO: it’s a politically based nonscientific topic. A war between American republicans and democrats that spread over the rest of the world with Al Gore. The people have been frightened into believing a bunch of blury idieas that were later discovered not to be true. The evidence is there but the public belief is slow to change.BUT ! The consequence of the hole anti carbon propaganda are really good. More renewable energy is being used.

    • Michael Cunningham aka Faustino aka Genghis Cunn says:

      Almost all work about climate change in the social sciences – and Judith Curry has linked to a lot of this work – starts off by accepting unquestionably that the scare stories are true – here Marshall says “We all know the facts” – which renders the work valueless. A typical approach is “What is the pathology of those strange and pitiful creatures who resist the one great truth of CAGW?” Hopefully, if you buy Marshall’s book, it might be more scientific, but don’t be surprised if its not.

    • JimboR says:

      Along a similar line here’s National Geographic’s take on it:

  • Mike says:

    Jonathan Paul Marshall it says a lot about people who applaud him.

  • bobo says:

    “Even then, it has been argued that that it implies a quantity — average global temperature — that is both mathematically and thermodynamically impossible to calculate.”

    Global average surface temperature is an estimation that has some usefulness because it describes some basic information about our zone of habitation. It is easily estimated in an independently verifiable way despite these subtle technical arguments (at the risk of derailing my comment, I can give another, irrelevant one: there does not exist any matter in the universe that is in a state of perfect equilibrium, therefore strictly speaking, nothing has a temperature).

    However, there are other metrics that have greater relevance than surface average temperature for deciding whether global warming is occurring. The climate system has several components (water, land, atmosphere, ice, biosphere); the only way to know for sure if global warming is occurring (and that a warming trend of some (sub)component is NOT due to a transfer of heat from another (sub)component) is to look at how the total amount of thermal energy in the whole climate system is changing. It’s a metric you seem to be very quiet about Don.

    Regarding changes in global temp in the past, how is that relevant? How does it follow that some forcing from the past is responsible for the current period of warming?

    It would be interesting to see the uncertainty band of the post-interglacial maximum graph (with MWP maxima displayed etc).

    • Don Aitkin says:

      Why don’t you do some work on it, and you could publish your results here.

      • bobo says:

        I appreciate the offer, I’ll try to put something together, it might take a bit of time though because I’m pretty busy at the moment.

      • Felix says:

        This is a question drvien by the politics of those who support it. Don’t believe me? Over the past thirty years, these are the same people who have been arguing to “save the whales”, the rainforests were disappearing, and that the Earth was about to enter into a new ice age. Yes, that’s correct, those same environmentalists were claiming the Earth was going into an ice age, then that it was going to heat uncontrollably, and now, since they realize they have no idea what the temperature is going to do (in fact, they’ve been predicting massive numbers of hurricanes due to the “high” temperatures, and each year they’re wrong), they’ve started calling it “climate change.”School has become nothing more than an opportunity to indoctrine students into liberal ideology.

  • Neville says:

    Don’t the urgers love their religious dogma? You can show them that there is nothing unusual or unprecedented about the slight modern warming when compared to the earlier Holocene and they ask how that is relevant. ( remember we are emerging from a minor ice age) Or they point to some silly study that has nix to do with weather/climate data , but plenty of irrelevant suppositions about who knows what.
    So let’s go further back to the previous Eemian interglacial and ask why temps were several degrees higher than today and SLs were at least 5 to 6 metres higher as well? Co2 levels also stayed at elevated levels 6,000 years after temp dropped into the last full glacial period before the Holocene. But why don’t these people tell us how to mitigate their imaginary CAGW? I’m sure Dr Hansen would be interested.

  • colin davidson says:

    What I think is most informative about the temperature proxies is that they are from Antarctica. Nowhere near Peru or Greenland. So much for the straw-grasp theory of MWP being only a local oscillation.
    Note the cycles. An Ice Age cycle with brief interglacials, the one we are in seems overdue for termination. That cycle needs to be in the climate models even if we don’t know what causes Ice Ages (which we don’t. Milankovich is flavour of the moment, but Fred Hoyle thought that was incorrect, and he was correct on so many other things – CO2 doesn’t cause major warming because of water feedback, the panspermia hypothesis, the prediction of a precise nuclear reaction (including energy level) which must occur because of the light elements. He said it was asteroids.)
    And then the well known Warm Periods within the interglacial. Not unusual, you can see them in the other interglacials too.
    As far as we can tell, these have a period of 1000years. These should be part of the climate models, but they’re not, again because we don’t know what causes them. At present solar magnetic field variation is a possibility.
    And the last plot, showing the three cooling/static periods quite clearly, with two warmings. The simplest explanation, unless you are an unquestioning believer, is that there is an underlying upward trend with a strong cyclic variation superimposed. You won’t see that sort of thing in the models. Adhoc guesses of volcanic influence, and aerosols is de rigeur.

    I’ve been scathing about the models in this post and I intend to continue. It is a scandal that the multi billions spent on the models have produced worthless rubbish which cannot predict temperatures within cooee of reality. And a greater scandal is that the so-called scientists who own the models have not acknowledged that the physical model they are using is flawed. And worse is the advocacy by some of these same scientists that we should revert to the stone age on the basis of predictions by worthless models created by the same worthless scientists.

  • Neville says:

    Dr Patrick Moore has offered a $100,000 wager that co2 levels in 2025 will be higher than 2015. So far he has received no takers. Yet thousands of these donkeys cheered after COP 21 and claimed the world had been saved from an apocalypse. But the biggest alarmist ( Dr Hansen) called them out and said that COP 21 was ” just BS and a fra-d.” At least Hansen understands simple maths and science. Of course that’s providing you believe that co2 is a dangerous pollutant

  • Michael Cunningham aka Faustino aka Genghis Cunn says:

    “But what seems almost indisputable to me is that there hasn’t been some kind of special ‘right’ climate for humans.” Indeed, you just have to look at the vast range of climates in which various people around the globe live today, we are a highly adaptable species and have increasing knowledge, resources and capacity to deal with whatever future befalls. We also know that our species almost became extinct in the last Ice Age, it has been estimated that the population at end-ice age was about 15,000. So no need to worry about climate until the next Ice Age is imminent.

    The major concern is not climate change, but why so many people accept it as THE most pressing issue of our age. Bizarre, unless you look at it in the light of Agenda 21 to bring about left-wing change. Even then, you would worry that so many apparently sensible people have been sucked in to policies which are clearly damaging to both our present and our future capability, particularly that of the poorer countries which activists so often claim to be concerned about.

    • Mike says:

      But it has increased by .08° since 1850 shock horror the sky is falling we are all going to fry! I would be glad that is all we need to worry about, you think there might be other things?

      • dlb says:

        I think you meant 0.8 deg.
        Don’t worry, increased convection will lift the sky back to where it belongs.
        Wonderful thing natural feedback cycles.

    • David says:

      In one sentence you say humans are highly adaptable. And in the next you tell me that the population dropped to 15,000 with the last ice age. That suggests human welfare is highly susceptible to changes in climate.

      • Bryan Roberts says:

        “you tell me that the population dropped to 15,000 with the last ice age”
        …but it probably didn’t start at 7 billion.

        • David says:

          This is Michael Cunningham aka Faustino aka Genghis Cunn’s” story.

          But if you are one of the “dropped” then it is a problem all the same. 🙂

    • Vishwaka says:

      Hi Jonathon.The arguments are very very thin and wtuohit any real evidence to support them. The reasons are financial and therefore political. That and laziness.Some governments don’t want to admit to it, or at least don’t want to take responsibility. Mainly because most economies are built upon the trading of the Fossil Fuels etc. And if they admit to it they have to stop trading in Fuels and move to green technologies which are expensive to set up and can cause political tensions with people they purchase e.g. oil from.Many PEOPLE don’t want to believe in it because:a) it’s actually quite a scary idea (that the actions of people could be endangering not just other plants and animals but our very own futures);b) it means people have to stop being lazy; andc) they have to change their lifestyles. For most this seems too difficult and so they would choose to disbelieve. For some it’s simply hard to change long-held ideas. And even those who DO believe will often do nothing about it because they say it’s not my responsibility’, why should I care’, or I’ll die before it gets too bad’.The biggest problem currently is the media (with the exception of the BBC who are criticised for being too supporting of current climate change being a human cause). Many stories on Climate Change will try to sow the seeds of doubt. It was strange to see (as I just watched An Inconvenient Truth on Fox Movies as it’s Earth Day) Al Gore demonstrate that in 2005(?) there were over 900 scientific studies published in journals on Climate Change where there was no doubt at all that human impact is leading to the current round of Global Warming, and yet of all the Media stories published in the same year on that topic, over 50% of them tried to cast doubt on the science. When all Scientific studies HAVE to be peer-reviewed (examined by other scientists) and all of them were found to show the same thing, it’s interesting the media wasn’t publishing info in the same way.People that talk about mass-conspiracies are fools as there are literally tens of thousands of scientists investigating some aspect of climate change and they almost all will say the same thing.As Trevor demonstrated, the arguments are childish, illogical, insubstantiated, and wtuohit any scientific evidence to support them.You have to make your own mind up where you stand on issues but please always bear this in mind: Do your own research, but research the SCIENCE using science journals and magazines and avoid the conspiracy theory sites as they will never provide the whole story only results that support their biased views. Remember, a scientist as a person may be biased and try to be misleading in his reports, but scientists as a group are unbiased and are simply looking for the truth and for a report to be published other scientists have to review it and decide if it’s a good study and carried out honestly.

  • David says:

    Don, when I see
    “… but a short-cut is that it [estimating an average global temperature] is as sensible as referring to the ‘average exchange rate’ of all currencies in the world today, or the average of all the telephone numbers in the telephone directory.”

    I worry that someone might read it. So I apologize if I am a bit tedious but temperatures are continuous data and telephone numbers are categorical data. You can take an average of continuous data but not categorical data. Stats 101.

  • Don Aitkin says:

    David, you seem often to jump to the computer keyboard without reading properly. This is what the summary said:

    ‘”A temperature can be defined only for a homogeneous system. Furthermore, the climate is not governed by a single temperature. Rather, differences of temperatures drive the processes and create the storms, sea currents, thunder, etc. which make up the climate”.

    He explains that while it is possible to treat temperature statistically locally, it is meaningless to talk about a a global temperature for Earth. The Globe consists of a huge number of components which one cannot just add up and average. That would correspond to calculating the average phone number in the phone book. That is meaningless. Or talking about economics, it does make sense to compare the currency exchange rate of two countries, whereas there is no point in talking about an average ‘global exchange rate’.’

    There is more that is relevant in the summary, too.

    Now, if you think that is wrong, you might set out why you think so, and why the authors are wrong. Since it is a peer-reviewed paper in a proper journal, you might also explain how the editor got it wrong. ‘As far as you can see’, if you will allow me, is not very far.

    • David says:

      “He explains that while it is possible to treat temperature statistically locally, it is meaningless to talk about a global temperature for Earth. The Globe consists of a huge number of components, which one cannot just add up and average. That would correspond to calculating the average phone number in the phone book.”

      I will stop you there.

      Don I know you do not have journal access but in the original article “Does a Global Temperature Exist by Essex, Christopher; McKitrick, Ross; Andresen, Bjarne in J. Non-Equilib. Thermodyn. 2007 _ Vol. 32 _ pp. 1–27, you will find that the authors stop short of making that claim. For exactly the reasons I discussed. I have copied a couple of paragraphs to give you some context.

      “…But if the statistics are not actually temperatures, what then are they? Can they be used as indices to warn us of subtle dangers, like the proverbial canary in the coal mine? Or are they just examples of an infinity of ad hoc numbers extractable from measurements that might be followed to no end?

      So far the proponents of global temperatures have been able to avoid this question. They have not substantiated exactly how changes upward or downward in their statistical measure or statistic might aspect dynamics and local states within the atmosphere and oceans. However, that has not stopped many remarkable attributions of cause: small increases in their global statistical measure or statistic have been cited to explain hurricane formation [13], viral infections in frogs [14], encephalitis in horses, and even pulmonary disease, delirium, and suicide in humans [15].

      The awkwardness of such claims is obscured because the concept of averaging is so routine. In fact, it is so pervasive that it may even seem implausible to mount a critique. But it should only be routine where it makes sense. Personal income and height are meaningful at the individual level, and no conceptual problems emerge when adding or averaging over a population. But
      there are certainly examples where averaging or adding destroys the meaning of a variable. In economics, for example, an exchange rate is meaningful when comparing two currencies, but the ideas of a ‘‘global exchange rate’’ or a sum over exchange rates are both nonsensical. Regardless of the fact that enough data exist to compute something analogous to a ‘‘global temperature’’ for the money markets, neither the level nor the trend in such a statistics would provide any meaningful information about the global economy. Another example : Individual telephone numbers are both meaningful and useful, while the sum or average over telephone numbers in a directory have no meaning.

      The notion of being globally ‘‘hotter’’ or ‘‘colder’’ for out-of-equilibrium systems is not altogether without merit. Miami in January, with temperatures ranging from 20 C to 30 C, say, is certainly warmer than Toronto at, say, -15 C to – 5 C. However, this ranking of relative warmth is not based on averages, but on the ranges in respective temperature fields. Since the ranges do not overlap, all averages will agree which field seems to be the warmer. It is independent of the choice of average.”

      Essex at al do not claim taking an average temperature “corresponds to calculating the average phone number in the phone book.” and neither should you.

      • Don Aitkin says:

        Thank you for extracting the material from the article. You are correct in saying that Essex et al do not go as far as the summary did. But they do say that the notion of a global exchange rate is ‘nonsensical’. And as I read the extract you provide what I infer is that the authors are dubious about the value of a global average temperature, and that they think others have made ‘remarkable’ attributions. The take-home message for me is this one:

        [The proponents of global temperatures] have not substantiated exactly how changes upward or downward in their statistical measure or statistic might aspect dynamics and local states within the atmosphere and oceans

        I feel this every time someone says that the hot December, or year, has produced the bush fires (or floods or droughts).

        Thanks again for a most useful contribution.

    • JimboR says:

      Don, you seem to be a big fan of the long if… “if this, and this, and this and this, then I’ll concede this”. To someone less versed in probability the inference might be that all of those planets will never align, so you’re not really conceding anything or you think what you are conceding is very unlikely. Unless you have a theory that warming reduces the probability of any of those other vital ingredients you list (for example: with warming there’ll be less arsonists, or less wind, or less lightning) then your conditional qualification is no more meaningful than the dots I replaced it with.

      As for what Christiana Figueres said Vs what the IPCC said, I’ll refer you again to what I said last time you made that dated claim (January 28, 2016 at 9:05 pm It seems to me that you, Christiana Figueres and the IPCC are all in violent agreement that warmer temperatures will increase the probability of bushfires.

      • Don Aitkin says:


        I am afraid that you are becoming boring. If you have a reasoned reply, then make it. But your opinion does not count for much. I have said this a few times before.

  • JimboR says:

    “I feel this every time someone says that the hot December, or year, has produced the bush fires (or floods or droughts).”

    Yes, although last time we drilled down on one of your examples of that, it turned out to be a bit of a straw-man argument. You need to listen carefully to what the experts say, rather than verbal them into something they didn’t say and then attack that. A recent example was your views on Christiana Figueres’ comments which after much kicking and screaming went from “ludicrous” to agreement:….

    “If there is continued warming then…… there would probably be more fires.” Don Aitkin says on January 29, 2016 at 1:28 pm

    (The “….” represent the statistical gibberish that I removed for you to improve clarity. My reply at the time shows why it can safely be removed.)

  • Don Aitkin says:


    You are having yourself on, I think, and rather rudely.

    If there is more warming, then other things being equal I would probably expect more fires, especially if there is more wind. But no one has yet shown that a particular fire, let alone all fires, have been caused by increases in temperature, let alone that strong winds are so caused. It is not so much increases in temperature per se, but long periods of high temperature in the same spot, which dry out the under-storey. A small increase in average temperature in Canberra, where I live, will have little effect if we have a few days of high temperature followed by a few days of milder, with some rain. The big fires in 2001 and 2003 occurred in periods of sustained heat, and were made much worse by strong westerly winds. In comparative terms, those years were a little cooler (always accepting the problems with average temperatures) than 2015/16.

  • Don Aitkin says:

    I went back to see what Ms Figueres had actually said. It went like this, according the ABC (22 October 2015), which is never wrong.

    ‘The United Nations says the New South Wales bushfires are an example of “the doom and gloom” the world may be facing without vigorous action on climate change.

    The executive secretary of the UN Framework Convention on Climate Change, Christiana Figueres, says the fires prove the world is “already paying the price of carbon”.

    “The World Meteorological Organisation has not established the direct link between this wildfire and climate change yet, but what is absolutely clear is that the science is telling us there are increasing heatwaves in Asia, Europe and Australia,” she told CNN.

    “These [heatwaves] will continue. They will continue in their intensity and in their frequency.”‘

    Setting aside the sloppy reporting (‘The United Nations’ turns out to be Ms F), Ms Figueres wants to eat her cake and have it too. No one , not just not the WMO, has established such directs links, and the IPCC’s SREX said so some years ago. The rest of what she says is just fatuous scaremongering.

    My acceptance of the proposition that a warmer world will probably have more fires is appropriately qualified. Ms F. I cannot take seriously. She is a propagandist for the AGW cause.

    • Ross Handsaker says:

      Don, regarding heat-waves, have you noticed that record/near record daytime temperatures coincide with low humidity levels. The highest daytime temperatures in Adelaide (where I live) are recorded when humidity is lowest. David Karoly commented on the low humidity levels during the South Eastern Australia heat-wave in 2009, although he blamed the high surface temperatures.

      Given water vapour is the dominant “greenhouse” gas, and that an increase in “greenhouse” gases is supposed to cause higher daytime temperatures, is it not strange that observations indicate an opposite effect?

    • JimboR says:

      Perhaps the social scientist in you could research whether arsonists, like the rest of us, prefer to stay indoors on extremely hot days? If you found something there I’d sit up and take notice of your long-if, but in the meantime it appears to be just a weak attempt to obfuscate the maths.

  • Don Aitkin says:

    Jimbo, Bobo and David,

    If you want to write a serious researched piece about climate change I’m happy to run it, but snarky stuff and lofty comments are just a waste of time; you’d be better off setting up your own websites.

    • David says:

      But Don, what about poor Margaret? There is only so many consecutive, “What another wonderful essay Don…” that any sane person should be expected to endure.

      • dlb says:

        What about the rest of us who have to put up with your incessant nitpicking David? If Don’s site was run like “Real Climate” you would be down the borehole sealed with six feet of concrete on top.

        • David says:

          Nitpicking; that’s research dlb.

          For example, Don’s initial claim that reporting a mean temperature is like reporting an average phone numbers, was wrong. What do you want me to do dlb, just let the comment go through to the keeper? Unchallenged? You are confusing me with someone else.

      • margaret says:

        ????? … Heh – yeah!$&@! …

        • margaret says:

          There were some nice, semi meaningful symbols but they just became question marks on posting – never mind – I had a small guffaw at David’s comment on my endurance of expressions of sycophancy …

    • JimboR says:

      Don, with regards your statement:
      “If there is continued warming then, given average winds, average numbers of arsonists and average numbers of lightning strikes, there would probably be more fires.”

      Imagine a game called Bushfire. You have four standard dice labelled Winds, Arsonists, Lightning, Temperature. You throw the dice, add up the four numbers and if the result exceeds 21 you win. After you’ve played a while, I offer to change the ‘5’ on your Temperature die to a ‘6’, and ask if that’s going to increase your chances of winning. Most sensible people (including Christiana Figueres and the IPCC) would say yes and move one. If I’ve done the maths right, I think it takes your chance of winning from 0.012 to 0.016.

      Now let’s translate your answer above to the terms and conditions of the game:

      “If you make that change, and I roll a 3.5 on the Wind die, and I roll a 3.5 on the Arsonists die, and I roll a 3.5 on the Lightning die, then I probably will win more often”.

      There are two problems with that answer:

      1. you can’t throw a 3.5 even though it’s the average result for each die. You could argue I’ve introduced that problem by using six sided dice, but I bet arsonist statistics come with decimal places too. In fact, what does “an average number of arsonists” even mean?

      2. even if we set that aside and imagine you did manage to throw a 3.5 on the Wind, Arsonist and Lightning dice, you don’t even need to look at the Temperature die. You’ve already lost the game. Precisely when all your conditions are met is precisely when the change I made to the Temperature die cannot make any difference to the outcome (3.5*3 + 6 < 22).

      A more reasoned response might have been:

      "If there is continued warming then, given the same wind patterns, the same arsonists patterns and the same lightning strike patterns, there would probably be more fires."

      or in terms of the game:

      "If you make that change, and the other dice continue to behave the way they always have, then I probably will win more often".

      That qualification could be a valuable contribution if you have a theory that the other dice behaviour will be impacted by the change to the Temperature dice (specifically, if your theory says the other dice are likely to give lower results as a result of the change to the Temperature die).

      Your statement as it stands now is simply wrong. Even if I give you the benefit of the doubt and turn it into my "more reasoned response" above, all you've done is add words with no theory to back them up. That's what I referred to above as your long-IF, and it's why I invited you to state your theory… pick a die, any die, and tell us why it's behaviour is likely to change to a lower value (e.g. arsonists like to stay indoors on extremely hot days).

      Without that theory, your qualifications make no difference to the statement, and you find yourself in violent agreement with the IPCC and Christiana Figueres.

  • […] But if the IPCC is correct, then what caused the similar warming trend from 1910 to 1940 shown in the third graph in essay #4? And why, given the great expansion of industrial activity in the postwar period all over the […]

    • David says:

      This goes to the whole reason we do time series regression. If every trend and correlation were well behaved we would not need the sophisticated techniques that identify trends in more noisy time series. Go an look at analysis of other time series data, e.g. crops, employment, exports, whatever. There are plenty of examples that exhibit similar volatility.

      • Don Aitkin says:

        So what are the sophisticated techniques that show exactly how the two warming trends have different causes?

        • David says:

          More information?

          • Don Aitkin says:

            The two warming trends of the same scale, one from 1910 to 1945 (not said to be caused by CO2) and the one from 1975 to 1998 (said to be caused by CO2, though the end point is plainly an el Nino).

  • […] Minoan period, when greenhouse gases, so far as we know, were not as concentrated as they now are (#4). We still  don’t know how much of the present warming has been caused by human activity, […]

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