In a comment to post on the Barton letters, Ed Snack claimed that

Michael Mann made an error in MBH98, he confused the square root of the cosine of the latitude with the cosine

Now if you look at MBH98, cosine latitude is only mentioned here:

Northern Hemisphere (NH) and global (GLB) mean temperature are estimated as areally-weighted (ie, cosine latitude) averages over the Northern hemisphere and global domains respectively

I did a bit of searching and found that Snack’s source is this

statement in the supplementary material for von Storch at al’s paper

“Reconstructing Past Climate from Noisy Data” DOI:

10.1126/science.1096109:

Our implementation of the MBH method essentially follows their

description in their original paper (S17). The statistical model was

calibrated in the period 1900-1980. Monthly near surface-temperature

anomalies were standardized and subjected to an Empirical Orthogonal

Function Analysis, in which each grid point was weighted by (cos

φ)^(1/2), where φ is the latitude (Mann et al. 1998

erroneously use a cos φ weighting).

But the area of the grid cells that MBH use is proportional to cosine

latitude and not to the square root of cosine latitude so I posted a

comment

suggesting that von Storch was mistaken.

Steve McIntyre then pounced on

my comment, presenting evidence that von Storch was correct. He even

stated that my comment was more worthy of criticism than McKitrick’s

mixing up of degrees with

radians in a journal paper

touted as a bombshell that refuted global warming.

It seems that if you want the output from PCA to be weighted by area,

the input has to be weighted by the square root of area. I don’t know

enough about PCA to know for sure who is correct here, but certainly

von Storch’s criticism has not been refuted, so I

retracted

my comment.

Neither von Storch nor McIntyre seem to think that the weighting issue

is very important. Von Storch just mentions it in passing and McIntyre

as not bothered to find out what effect it has on the final

reconstruction.

Nonetheless McIntyre repeatedly demanded that I post a ferocious

denunciation of Mann’s weighting error. He felt that I was obliged to

do this because my single post on McKitrick’s mixing up degrees with

radians when calculating the cosine of latitude meant that I

specialized in cos latitude problems. Now his demand is rather

irrational. Firstly, “cos latitude problems” is a gerrymandered

category engineered to create a false equivalence between McKitrick’s

error of using degrees when he should have used radians in a linear

regression and Mann’s error of not taking the square root of his

weights in a Empirical Orthogonal Function Analysis. Secondly, one

post out of almost 800 on this blog does not make me a specialist on

that topic. Thirdly, even on a topic where I do specialize, like,

umm, Lott, I still don’t have to post on every little move Lott makes.

I explained this to McIntyre, but he insisted that I was this strange

“cos latitude specialist” thing. I don’t think he was doing it to annoy me—he seemed to have completely convinced himself. He then felt entitled to

deliver a stream of jibes and insults, accusing me of hypocrisy, of

being petulant and of being a troll. He does this to others as well,

calling Gavin Schmidt and

Caspar Amman “Dumb and

Dumber”

He also falsely claimed that I attributed McKitrick’s degrees/radians

mix up to McKitrick and McIntyre and falsely claimed that my

criticism of Essex and

McKitrick was “mostly just

belligerence”. Nor would he correct these falsehoods.

If McIntyre’s dealings with climate scientists have been anything like

his behaviour towards me, with his irrational demands and unpleasant

manner, I can certainly understand why they might not wish to

correspond with him.