A statistical study on temperature proxy reconstructions has been submitted to the
.
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 CO
2, 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.
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*Or do we?
**this, of course, shows why the CRU's refusal to release its data was so utterly shameful