Tuesday, 17 August 2010

Is Global Warming Dead?

A statistical study on temperature proxy reconstructions has been submitted to the Annals of Applied Statistics.

I'll admit, that's not the catchiest of introductions to a blogpost. But bear with me - this is important. Seriously.

The Annals of Applied Statistics is apparently one of the “top statistical journals in the world, although I can't vouch for that personally. The article in question is listed to be published in the next issue. From that, we can infer that the article is a good one. If you can't wait for the next issue, of if (like me) you don't subscribe to that particular journal, a copy can be downloaded from here. I encourage you to do so; it is very readable, and not just by the standards of statistical journals.

The article looks at the statistical quality of the correlation between long-term temperature proxy data and actual historic temperatures. That still sounds fairly dull, even by the standards of statisticians (who, generally, are the mathematicians who were too detached from reality to become accountants). However, this is a crucial subject. It is, I think, about time that I explained why...

We all know that Global Warming (GW) is a huge issue, and is being used to justify many and varied laws and policies. Politicians neatly side-step questions of whether GW is real, by pointing to an impressive array of scientists who tell them that GW is real. That enables the politicians to treat GW as fact and not enquire any more deeply. So the justification for the political influence of GW rests on the scientific foundations of GW.

So, how does a theory gain scientific acceptance? Simple - by use of the "scientific method", a term that many have heard of but surprisingly few understand. I say "surprisingly", because it really is very easy to understand if anyone actually makes the effort to explain it. In short, the scientific method requires that you think up an idea about how things might be (you can call this a "hypothesis", if you like impressing people). Then you go and see if things really are like that (again, amongst those that like to use fancy words, this bit is called an "experiment"). Note the order of these two steps; first you develop the theory, then you go and test it.

Testing is quite a hard step, in fact. You need to design your test so that it is only testing your idea, and is not influenced by other possible factors that might be varying at the same time. For example, if my theory was that readership of a blog increases with the rate of posting, I could do that by simply writing more posts - but I'd have to make sure that all of the new posts were of a similar length, quality, readability and so on compared to before. I would need, in short, to control all the other possible factors so that if I saw a change, I could safely attribute the change to the factor that I was deliberately varying. Common sense, really.

So the basic principle is that you develop a theory, and then you go and see if it is true by way of a test. In the case of GW, the theory arose from computer programs that tried to model the way in which the Earth's atmosphere worked. They suggested that increasing levels of CO2 in the atmosphere led to an increase in global temperatures that could become uncontrollable. That is obviously not a good idea, if it is true. But is is only a theory at that stage. We need to test it, to see if it is true. Until then, we cannot claim that it is a scientific truth. All we know if what some equations running on a computer tell us - we can't have any confidence that this says anything about the real world until we test the theory out.

The easy way to test it would be to pump lots of CO2 into the atmosphere and see what happens. However, as the point of validating the theory is to find out whether we need to stop emitting CO2, that approach is problematic.

An alternative would be to use a different planet - pump that full of CO2 and see what happens. Or, extract all the CO2 from its atmosphere instead. However, we don't have one within handy experimental reach.

So, the only test of GW is to look at the past, instead. We know that CO2 emissions have increased hugely over the past centuries as industrialisation has progressed*. Therefore, GW predicts that global temperatures should have been steady for centuries until the Industrial Revolution, following which they should have increased steadily up to today. All we need to do is look at the varying temperatures over that period.

There is a snag, though. We have only had (a) decent thermometers and (b) people who obsessively record temperatures since about 1850, whereas to prove the point we have to compare with the temperatures before then. So, we have to use a "proxy", i.e. something else that we can measure, which correlates with temperature.

There are, gratifyingly, many and varied proxies. Between them, they cover the last thousand years or so. Sadly, they all give us different sorts of measurements - tree ring data gives us thickness measurements, ice core data gives us isotopic ratios, and so on. We need a way to convert these to temperature data in units we understand. Fortunately, there is a way to do this, because there is a period of overlap in the 150 years from 1850, where we have both hard thermometer data and proxy data. So what you have to do is plot the proxy data for this period against the actual temperatures and use that to work out what the relationship is. Obviously, there won't be a perfect one-to-one correlation, due to experimental error and outside factors. So you need to apply statistical methods in order to work out the way in which they are related. A computer can do this, provided that you program it correctly. Then, you apply the program to the old proxy data, and it gives you temperatures going back a thousand years.

Then, you have the temperature data that you need in order to validate (or refute) the prediction made by the atmospheric models. If that data validates the model, you have a scientific basis for saying that the model accurately reflects the influence of atmospheric CO2 on the Earth's climate. With that basis, you can predict that unless CO2 emissions are curtailed, disaster will follow.

On the other hand, if the temperature data does not show a steady temperature in pre-industrial times followed by a dramatic rise since we started to emit CO2, then you have a problem. Specifically, your atmospheric model has been shown to be wrong. I'm emphasising that word - wrong - because there are plenty of weasel words that can be used, but in the end they all boil down to the model being wrong. If the model is wrong, its predictions are also wrong (the GIGO principle), and the basis for years of climate hysteria suddenly vanishes.

Now, if you were alert, you will have noticed a small proviso: I said that a computer can do the necessary correlation work, provided that you program it correctly. Up to now, that programming work has been done by climate scientists. The significance of the paper that I linked to way up there at the start of this post is that a pair of statisticians have pointed out that this is a statistical question, not a climate science question, so surely it should be done by statisticians? Not only that, they have also re-done the work, using the proxy data provided by climate scientists**.

Their findings?

First, they have a number of criticisms of the manner in which the climate scientists approached the statistical issues in question.

Second, when the maths is done properly, the temperature data does not support the GW hypothesis.

I'll say that again: the temperature data does not support the GW hypothesis.

Their results show that the theory of Anthropogenic Global Warming is wrong.

Now, this post is titled "Is Global Warming Dead?", not "Global Warming Is Dead", for a reason. That is, there are several comments in the paper which are carefully worded so as to remain scientific in nature, but which could be seen as somewhat barbed. I am concerned that the authors may have approached the issues with a pre-existing opinion on GW - in which case the risk of confirmation bias applies to them (and me) just as strongly as it applies to many climate scientists and GW activists.

But whichever way you read it, this paper is a huge problem for GW.


*Or do we?

**this, of course, shows why the CRU's refusal to release its data was so utterly shameful

(Hat Tip to the
Watts Up With That? blog)


  1. statisticians (who, generally, are the mathematicians who were too detached from reality to become accountants}

    Hmmm .. So a statistician is an accountant, but without their sense of humour.

  2. I know a good joke about accountants. It will have to wait for another day.

    What a turgid paper, all 45 pages of it, and I have never seen a reputable statistician state statistics will break out of along established range as that undermines their reason for existing, it is improbable and statisticians do not have imaginations either. The culmination came on page 42. "Nonetheless, paleoclimatoligical reconstructions constitute only one source of evidence in the AGW debate."

    So before dismissing GW, please may we return to the hypothesis I have consistently put forward? The planet is a self-correcting system (Gaia) hence the relative stability of the temperature range over millions of years until there is an event, such as a meteorite or man's interference, that push the system beyond its
    auto control. My evidence, to broaden your horizons, is that the Antartica is melting at an unprecedented rate. So is the Arctic.

    I have not been there to measure it and I must rely on others to do that but that is what I read. I do not know if it is water vapour or carbon dioxide in the atmosphere as the cause of forcing the environment to react like this. You correctly advocate rigour in science but all the evidence must be evaluated. You
    must be careful not to undermine fears of GW in my view when other evidence points to it, but there is no doubt in my mind that old extrapolations have now been discredited. That will prove a disservice to the many scientists who maintain high professional standards and do not jump to conclusions. Good spot P but don't be blinkered. ;-)

  3. Posted from an iPod which is in as infuriating as posting a comment from an iPhone. It is virtually impossible to scroll through after the comment is written without making more mistakes on returns. The technology will get better but it is still pretty frustrating at present. :-)

  4. Well, I'll happily give the Gaia hypothesis some thought, if it is a proper hypothesis. What does it predict will happpen, that we can then test?

    You point to melting ice, but (a) that is the experience which leads you to the hypothesis - the next step is to apply the hypothesis and produce a verifiable prediction, and (b) my understanding is that ice cover is actually increasing again.

    The problem for GW is that it relies on its scientific basis for its authority. That, in turn, requires it to be a proper scientific theory. That is only true if it makes predictions from the data which can be verified - which means the historic temperature/CO2 emissions correlation. Other sources of evidence are ex post facto (e.g. "We just had a hurricane!! OMG! OMG! Global Warming is here!") and thus do not add to the scientific basis of GW.

    Without the historic climate evidence, GW is in trouble.

    don't be blinkered. ;-)

    Quite right - I am trying, really.

    And finally, I do agree re iPods & Blogger... something should be done! :-)

  5. We could be up all night on this one. ;-)

    2. A self-regulating system is not difficult to understand, but it is very difficult to model and to measure. However, the volume of ice at the poles must be a key indicator as to the state of the environment from any common sense point of view. Just think about it.

    Please have a look 'Understanding Antarctica' http://www.antarctica.ac.uk//about_bas/publications/corporate which includes some interesting statistics in print by the British Antarctica Survey, a highly respected body.

    As for other evidence for global warming, please look at http://climate.nasa.gov/evidence/ where the links to various scientific papers will keep you occupied all afternoon. To cite some of the key statistics given:

    # Antarctica has lost 36 cubic miles of ice between 2002 and 2006.

    # "Small" glaciers have decreased in length by 12m (9,000 cubic km of water) between 1961 and 2005.

    # The frequency of "extreme" events , ie outside previously recorded ranges, has increased noticeably in the last decade.

    # Since 1750, the acidity of the ocean has risen by between 20% - 30%. (I consider this to be significant and the methodology etc. is worth further investigation.)

    So, P, why without historic climate evidence is GW in trouble? A graph can start from any origin *rebased at x=0, y=0* at any time and even from today, there is evidence that the risk of GW is real.

    Where is your evidence that ice cover is increasing? Admittedly it will do so on a seasonal basis.

    From my amateur observations, man's activity on the surface of the planet must give rise to concern as we burn carbon based fuels at an unprecedented rate and standards of living are set to rise in Asia and the Far East. The effects of this will manifest in many ways, so dismissing GW because of erroneous global temperature extrapolations is blinkered. ;-)

    Finally, to assuage my conscience, I ought to qualify my comment that statisticians do not have imaginations. They do have imaginations, just not creative ones. :-)

  6. It missed out 1. Aren't you relieved?

    Sorry my links aren't live. I thought they would be. Silly iPad.

  7. And do you have a comment on the subject of the post, which is the loss of the scientific basis for the theory of AGW?

    The problem with your examples is that they are observational. For AGW to be true, three conditions must be satisfied:

    1. The world is actually getting warmer
    2. This is because of what we are doing
    3. It must be possible for us to stop it

    (Nigel Lawson adds a fourth, which is that the cost of stopping it must be less than the cost of allowing it to continue)

    Your observational examples only help with the first. Assuming that the world is actually getting warmer (despite its average temperature declining for the last 10 years...), then given that the world's climate has varied hugely over time it is quite possible that any current changes are simply another instance of that natural variation. If so, we would be better to direct resources at coping with the change rather than directing them at a Canutian attempt to stop it. That could in fact involve increasing our CO2 emissions, although I would hope it did not.

    If we get this wrong, and waste our resources on a futile effort to stop that which we did not cause and cannot stop, then the opportunity cost of that could be huge and shameful. The principal losers would (imo) be those in the third world who were denied the chance to develop their way out of poverty, and therefore this is also a moral issue.

    Therefore, the question of whether AGW has a scientific basis is crucial. If we can show through the scientific method that GW is both real and caused by CO2 emissions, then we know that we need to take one specific action - reduce those CO2 emissions (if Lawson's condition is satisfied).

    However, the cited paper shows that this is not true. It shows that the AGW hypothesis is wrong. It shows that there is a huge potential risk in simply trying to cut emissions.

  8. Your opening comment above is unwarranted. The title of your post is "Is Global Warming Dead?" and I agree that it is an important issue, although I see no reason to widen the arguments as you appear to wish to points 2 and 3. I have no desire to discuss the politics of the matter apart from noting that the result of rising sea levels and the inability of plants and animals to adapt will be just as critical as "those in the third world who were denied the chance to develop their way out of poverty" and I am not as naive as to believe that there are no political overtones to this matter.

    What I was demonstrating that in the debate about GW actual temperatures do
    not need to rise as we are observing other phenomena which are attempting to regulate the Earth's surface temperature. Furthermore, parameters are required so global warming is defined in its purist sense are we measuring temperature during the last a decade or a century or longer. The statisticians had difficulty with this and were only discrediting the extrapolations. They acknowledged other observations, which under my hypothesis of a self regulating system (Gaia)I would regard as evidence, require further investigation. I prefer a holistic approach where the whole is more than the sum of the parts.

    Therefore the cited paper can show that the current scientific basis is untrue but that does not mean GW is dead; perhaps within natural variation the world is not actually getting warmer, as Lawson stated in 1, but there is enough evidence manifesting itself to suggest that it will and at that stage we will be unable to moderate the rise unless we act have acted responsibly beforehand. I think the jury is still out, but at least I have provided evidence previously that you should put into your pipe. ;-)

  9. Ah, but you are assuming that the temperature change is due to us - a crucial assumption. If it is not, then how can we stop it? And if we cannot, what must we do to prepare for higher temperatures? (assuming that they are indeed nigh)

    Now, you may say that it is obvious that it is down to us, but (a) that is a somewhat anthropocentric approach and not a scientific one, and (b) if it is so obvious, there will be no problem in developing a testable scientific hypothesis to prove that.

    And so we return to the start; that GW theory presents a believable mechanism by which our activities may have warmed the Earth. Sadly, though, the believable hypothesis has, under testing, failed.

    So, do we try to stop GW and possibly fail, or do we try to cope - which hedges our bets and works either way?

    I know where I sit. Science will budge me from that position, but I see precious little of that happening.

  10. Why is it a crucial assumption that GW is anthropogenic?

    The sun appears to have changed phases. Earth no longer has the protection from solar winds that it once had, but that doesn't mean that man's actions are not contributing to magnify this effect and GW cannot be tackled in a number of ways.

    Let us agree that:

    1. Matter on this planet does not disappear.

    2. Man is burning day in, day out significant amounts of carbon based fuels.

    What I can't understand is why scientists have relied on temperature variations to demonstrate GW, when the regulating mechanisms of the plant such as the oceans, the glaciers, faster plant growth, Antarctica (not the Artic - wrong tilt) leave temperature as a final indicator that these other mechanisms are failing. Why doesn't a mathematician model the huge amounts of carbon in the system? If they can model the water cycle, they should be able to calculate the carbon pumped into the air, in the atmosphere, in water and in living organisms to work out the pathways and discrepancies. The paper you highlighted demonstrates that the historical statistics on temperatures can be made into whatever you wish in truth so nothing has been proved. I will agree on that.

    You must acknowledge that until we crack the hydrogen solution, conserving carbon-based fuel is a sensible policy, whether the GW justification is erroneous or not. That consideration might budge you to believing the steps being taken to combat GW are sensible if the science on GW doesn't emerge. However, I think it will increasingly. Want a friendly bet, P?

  11. The assumption that GW is anthropogenic is crucial for the simple reason that if it is caused by something that is out of our control then it is, by definition, out of our control. If we cannot stop it, we are best advised to find a way to cope with it.

    Ah - you may say - but even if it is caused by something else, we can simply reduce CO2 emissions in order to compensate! To which the simple answer is yes - but only if lowering CO2 emissions does actually reduce the Earth's temperature (in which case GW will be anthropocentric). So, either way, we need there to be proof of a link between CO2 emissions and temperature. If that link is scientifically disproved, then the whole GW movement has problems.

    As for why mathematicians don't model the carbon system, the glib answer is that mathematicians don't do that sort of thing. Mathematicians are like toolmakers; they don't actually fix your car or build a new one, but they create the tools that enable others to do so.

    So as for why climatologists or geographers don't model the carbon cycle, well that's simple. The mathematicians concluded long ago that it is impossible to model these things. Which doesn't stop people trying to model the weather, it just means that their predictions need to be taken with a healthy pinch of salt.

    Conserving carbon-based fuel? Absolutely. The stuff is finite; we must conserve it. But there is a huge gap between that, and the demands of the GW lobby.

  12. It is the small things in life that make a difference.

    Have you seen the beaucracy of the IPCC? So many chefs. I think evidence supporting GW will continue to emerge. You are right. We can waste much time, energy and other resources on the wrong solution.

    Not a betting man then? I was so looking forward to collecting my winnings in person. ;-)

  13. M & P I haven't read all these comments, so sorry if I am repeating what has been said already. But:

    Isn't the key that AGW is an a priori
    thesis? It is based on the assumption that CO2 is a greenhouse gas, and therefore must be having an effect on the climate. Once this is held, then provided sufficient CO2 is being pumped upwards, the temperature should be climbing. If it isn't at the moment, that will only be because of some other counter-balancing thing that is "artificially" keeping temperatures down. This is why I think this bit needs thought:

    if the temperature data does not show a steady temperature in pre-industrial times followed by a dramatic rise since we started to emit CO2, then you have a problem. Specifically, your atmospheric model has been shown to be wrong.

    The error (if there is one) therefore of the AGW theorists is in assuming the amount of CO2 in the atmosphere is sufficient to change the climate.

  14. Hello Albert,

    I was hoping Patently would reply, but I suspect from his tweets he is tackling his extensive 'to do' list.

    You definitely have a good approach, but I won't even try to pretend to understand it all. My practical knowledge only extends to bubbling CO2 through limewater to detect its presence. Chemical reactions go on in the atmosphere at every level and it appears that the increased presence of water vapour, another greenhouse gas, complicates matters further amongst other things.

    The point really was that Patently ended his post with But whichever way you read it, this paper is a huge problem for GW. and I have attempted to explain to him that in fact it isn't. You have understood in that this will only be because of some other counter-balancing thing that is "artificially" keeping temperatures down. but, I ask myself, has Patently?

    Vroom Vroom. ;-)

  15. Hello measured,

    Are you suggesting climate change makes P's blood boil? At least he'd have to admit there's some warming going on.

    I understand all this much less than you, having never bubbled CO2 through limewater (or if I did, I don't remember doing it - the only thing I remember from my science experiments was burning my teacher's hand from which I learnt that if you put a metal rod in a busen burner, it becomes hot - not terribly useful to me it turns out).

    While we wait for P's response to my post, have you seen Young Mr Brown anywhere? He seems to have disappeared off the face of the blogoshpere. Perhaps he's been bubbled through limewater.

  16. Hello Albert

    I haven't seen YMB. I only posted on his site once or twice quite a few months ago. He doesn't post regularly. I do not know anyone, apart from P, who knows him. Sorry.

    Your poor teacher. You did not need science lessons to teach you about burning hot pokers, but actually that experience may have shaped your life. You obviously remember it vividly. No life is uneventful.

    Blood boiling? Well, I think P is rather hot. Hang on, perhaps I should rephrase that. No, I won't. It will cheer him up after his chagrin of being beaten by a woman. Hang on, perhaps I should rephrase that. Nah, a bit of spanking raises expectations. Enough!???

  17. actually that experience may have shaped your life

    Not really, he was gracious enough to realise it was his fault. He asked me to hand him the rod, and I, being a very obedient pupil, did so in the heat of the moment, as it were. The only thing I learnt from that teacher was the importance of being fair - not a bad lesson I suppose, so perhaps it did shape my life. Depends on whether I am fair myself, I suppose!

  18. Are you really sponsored by an oil company, P?

    It was just that I heard rumours. ;-)