Dear dr Mann, dr Bradley and dr Hughes,


I am working on a long (10 page) cover story on the Hockey Stick for Natuurwetenschap & Techniek, a Dutch monthly science magazine which is comparable with Scientific American.

I have made a detailed analysis of MBH98 and also of the work of McIntyre & McKitrick (MM) and Von Storch & Zorita. I also studied your latest comment on MM04 on the weblog www.realclimate.org (dd 4 December)

In my opinion there are some issues still open on which I would like to hear your comment. This could be done by email, but I would prefer to call one of you and discuss the topic by phone.

Here are the issues:

1) How do you explain the existence of the directory BACKTO_1400-CENSORED on Mann's ftp-server? MM show that it contains the results of the calculation of the NOAMER PC's without using the bristlecone pine series, giving a higher NH temperature in the 15th century.

2) There is a severe debate between you and MM about the skill of the calculation. You claim a high RE-statistic. MM show that their simulated hockey sticks also give a high RE-statistic but a very low R^2 statistic. In MBH98 you didn't calculate the R^2 statistic, but in Mann and Jones (2003) you did. I asked Eduardo Zorita questions about this and he said he would calculate both. Why didn't you calculate the R^2 in MBH98?

3) On the weblog www.realclimate.org you state that MM should use 5 PC's in the NOAMER-network if they use conventional PCA. Especially the PC4 is important while it accounts for the bristlecone pine series. This means that the overall result in MBH98 depends on a single PC4. This is in contrary with the claimed robustness of the MBH98 method. Do you agree now that the robustness of MBH98 is lower than originally claimed?

I am looking forward to discuss these issues with one of you. If for time or other reasons you're not able to respond to this email before Friday, January 7, could you please give me a short reply.

Yours sincerely,

Marcel Crok