Who’s in Denial
Posted by Jeff Id on November 5, 2009
William Connolly has been gracious and not snipped any of my comments on the Tiljander debate at his blog. I’m about ready to add him to my blogroll so this isn’t an attempt to bash his blog, however he wrote a beauty of an explanation as to why it’s ok to read thermometers upside down again. It never ceases to amaze how far people can go to reason into almost any position. It’s like people who complain about the idiocy of government and continue to vote for more, like that will fix it. Anyway his rationale is entertaining.
Imagine a climate proxy, accurate over the last 2kyr, that shows (for example, let us suppose) a warm period around 1000 AD and which, undisturbed, would show the recent warming. Further suppose for definiteness that this proxy is of such a nature that increases in the proxy value represent increases in temperature. Imagine this proxy is contaminated with non-climatic signal over the last 200 years, enough that the climatic signal is overwhelmed. Suppose that this contamination is of such a nature that it leads to a strong decrease in the values of the proxy over the last 200 years. Such a proxy (call it A), fed into the Mea algorithm, will be flipped over (due to its negative correlation with recent instrumental temperature) and will contribute a net cold influence around 1000 AD. How much it contributes will depend on how well it correlates to recent times.
Now there isn’t anything wrong with this paragraph that I can see. He’s got a good handle on the multivariate nature of some of the regressions. Consider that last sentence (which is correct) how much it contributes depends on how well it correlates. Dead on for one of my biggest criticisms, these regressions are a form of data sorting and are just as significant a no-no as the data elimination sorting where data is physically thrown away. I think of the weightings of a MV regression like modulating the data (information) partially away rather than fully. The fact that the modulation occurs on a correlation basis makes the complaint about the method exactly the same as the correlation based elimination methods.
Not good in my opinion but what can we do.
The next paragraph:
Now imagine a similar proxy, except the nature of the non-climatic contamination is such as to add a strong increase over the last 200 years. We’ll call it B. This time, the proxy won’t be flipped over, because its correlation to recent times will be positive. But the variance into the past will be strongly de-weighted (because we’ve just added an artificially large postiive trend). So it will imply not much change around AD 1000. But now we see this, we can see that the same problem applies to series A: unless, by bizarre co-incidence, the negative non-climate signal just happens to match the true positive instrumental signal, the variance in the past will be wrong. And since we’ve had to assume that the non-climate signal overwhelms the climate one, its likely that the recent variance will be too large, so the past will be de-weighted.
So he makes the assumption that the positive trend in the contaminated signal is larger than the result. I’m not sure he’s looked at HadCRUT lately but I’m not certain the assumption is valid. Let’s assume it is though. So he’s saying that Tiljander doesn’t matter upside down because the real climate signal – which there isn’t one – is deweighted by some fraction (say 50 percent) and averaged. So the inverted signal is deweighted to a point that William has defined it as a red – herring.
Well everything was going well until the conclusion. There are 4 tiljander proxies in Mann 08 three of them were inverted and they all have huge blades even after the log of the varve thickness is taking one of the biggest leaps of faith I’ve witnessed to convert it to temp.
It’s rather amusing considering that the assumption is for deweighting where there is absolutely no evidence that deweighting occured. In fact the Tiljander proxies (specifically the known bad data portion) correltated well (strongly negative) to temperature and therefore were flipped over and probably received reasonable sized weights. Even that’s not the point though. We already know that each tiljander series is 1 of 484 which passed correlation screening. Even with full weighting equal to every other proxy it’s 1/484th of the reconstruction. Nobody ever expected fixing Tiljander to fix Mann08. Mann 08 is a disastrous attempt to kluge together a hockey stick, nothing more. It’s worth adding that there is a good chance the series was more heavily weighted than William asserts but it still wouldn’t move the result very much.
The point is that the thing was used upside down. It is known, thermometers read upside right (even in kindergarten) and therefore flipping them is an error. Even in kindergarten the teacher would tell you to flip it the other way round Mikey. The physical meaning of the Tiljander proxy is warm weather melts more glacier and carries more sediment. Flipping it upside down changes the physical interpretation to warm weather freezes more water and carries less sediment.
In case you were wondering, this does not make sense. The most Bizzarre thing about it, is the continued defense of this pile of poo for a paper.
Yesterday, in a fit of idiocy I took a stroll around Real Climate. I found Michael Mann (who claims to be somewhat conservative) pounding on every conservative institution he could find about climate disinformation. How many analogies are there, pot and kettle, glass house, pants on fire. Why he didn’t just say oops, flip it, claim no change and move on is beyond me. It could have been a huge PR win that would make the important, equally flawed yet difficult for laypeople to figure out part of his case sound reasonable to the public. Instead we get denial, absolutely goofy answers from Mann and now an odd hand waiving half-endorsement by a well educated AGW believer of an obvious mistake.