I am at a loss as to what you hope to achieve in this continuing spat with Mann et al. If it is to prove that the paper of Mann 98 was a dubious bit of research, I would agree, he has even admitted there are problems with it himself?

Paul, Mann et al still do not acknowledge a fraction of the flaws in their temperature curve that Steve has highlighted, although they were forced into publishing a correction to their study in nature, it does not go so far as to address many of the problems Steve has unearthed. They still staunchly defend it, whilst adding many of the caveats that other papers are now more relevant etc. etc.

However, that research is seven years old.

That research is still used extensively, in the media, in “scientific” reports, summaries, lectures, and by political pressure groups. The research is old, but the use of the graph is “current”. It is not so much Mann who needs to know that the curve is flawed, but those that use it so extensively, and the wider public audience.

Proving it or disproving it to be correct will not determine whether global warming is proved or not.

Runaway anthropogenic global warming will probably never be proven or disproved by a single study. It will always be a jigsaw. The direct warming effect of CO2 is relatively small, and only becomes dominant through positive feedbacks in computer models. Any one scientist is really forced to look at one aspect of a much bigger problem. The historic temperature record is a massively important part of this jigsaw though, because it can tell us if todays warming is within natural variability or quite unprecedented, and it is also used to “tune” computer models (not that this has any great meaning – another story!). This is where the Mann curve comes in; the key is the complete lack of variability from 1000 to 1900, compared to others (e.g. Moberg) which shows highly variable temperatures.

If your aim is to point out the weaknesses in climate research in general, then surely time an effort of all sceptics would be better spent scrutinising more recent work

Steve is trying to do this, it can be seen in other posts, but he has run into a brick wall in obtaining sufficient information about studies to replicate them. Mann was originally quite forthcoming, although his quality control was questionable, until he realised that Steve was attempting to replicate his work, when he also refused to answer questions. Steve’s efforts have been a true uphill struggle in that most of the work he is either having to derive from scratch or reverse engineer results, which is never easy.

Incidentally, as I see it, your reconstruction of Manns data showing the 15th century to be warmer than now is even more damming than Manns original construct, as it indicates a gradual decline in global temperatures until 1850, before human influence reversed that trend.

Don’t forget, climate is a chaotic system – much like the weather – which swings up and down depending on many factors. It would be wrong to extrapolate a single trend for a long period of time. Perceived wisdom on historical temperature (pre-Mann) was that it was warm during the Roman empire (~2k years ago); cold during the dark ages (~1500 years ago); warm during the medieval warm period (~900 years ago); cold during the “little ice age” (~300 years ago) and then warm again today. Most sceptics claim that todays temperatures lie within these variations – as indicated by Steve’s reconstruction. Most AGW supporters claim that todays temperatures lie outside these bounds. However it is important to note that Steve’s reconstruction (like Manns) does not carry sufficient statistical skill to be used as a reliable temperature record.

Unfortunately the science is not as simple or as clear cut as just looking at the Vostok ice core record. It is necessary to relate the CO2 concentration to the effect on climate. Remember that direct greenhouse effect from CO2 is quite small; the predictions rely on positive feedback from other effects (particularly water vapour feedbacks, a far more significant greenhouse gas) to cause substantial warming.

For example, if you accept that the CO2 concentration was low a thousand years ago, why does it seem likely that temperatures back then seem to be warmer than today – there is a huge amount of evidence to support this in the Northern Hemisphere, and a growing band of evidence to support the theory that the Southern Hemisphere was similarly warm during this time.

If CO2 is the dominant forcing, low CO2 coupled with high temperatures does not stack up well, which suggests there are other forcings which are more likely to dominate global temperature. The Mann “hockey stick” was the main attempt of the IPCC and others to demonstrate that the medieval warm period did not exist; but we now know (thanks to Steve) that the Mann curve is simply an artefact of bad statistical analysis.

Furthermore, there are other CO2 records – such as the leaf stomata records – which suggest that 300+ppmv CO2 is the norm in the holocene. This study does suggest a closer link between CO2 and temperature, but if you accept this study you have to also accept that the CO2 concentrations we are seeing today are not so far outside the bounds of natural variability.

I am at a loss as to what you hope to achieve in this continuing spat with Mann et al. If it is to prove that the paper of Mann 98 was a dubious bit of research, I would agree, he has even admitted there are problems with it himself? However, that research is seven years old. Proving it or disproving it to be correct will not determine whether global warming is proved or not. Neither side will now back down because reputations (and in some cases careers) rest on it. Why not agree to disagree and move on. If your aim is to point out the weaknesses in climate research in general, then surely time an effort of all sceptics would be better spent scrutinising more recent work, than a single 7 year old paper. Incidentally, as I see it, your reconstruction of Manns data showing the 15th century to be warmer than now is even more damming than Manns original construct, as it indicates a gradual decline in global temperatures until 1850, before human influence reversed that trend.

I’ve been skeptical of "Global Warming" and the Kyoto Protocol in particular since my time in Japan. It seemed like the organizers were more interested in a lavish event than the enviroment.

Keep up the good work — and please post on Tim Barnett’s recent paper. I’m distrustful of it because he is on record as saying, "Anyone with doubts about man’s role in global warming is an idiot."

Still, if it is the real deal, then that is great — but it won’t say that we should adhere to the Kyoto protocol!

Steve: That’s a really ironic story and hard to understand how the forest was interfering.

Anorth story like that: a dendrochronologist was studying a bristlecone pine and for some reason decided that he would get a better sample by a cross-section than a core. So he cut down the tree, which, when dated, was the oldest tree in the world. I’ve got a copy of the academic article reporting on the tree.

It is curious what doesn’t get covered. I was in Venezuela on business in (I think) 1993 when Chavez led an insurrection against the then government. The hotel that I was staying in looked down over an air force base that was involved in the insurrection so the hotel was attacked. There was a pretty fierce machine gun battle in the parking lot. The guests were all evacuated to the basement of the hotel. It was a strange day. The next day I got pinned by sniper fire in an alley for a while. There was virtually no coverage of the rebellion in the outside world.

Steve: Red noise has persistence; I suspect that what you understand by pink noise is similar, but with less persistence. The simplest red noise is autoregression and if you think of it being generated by a blend of the lag-1 value and white noise, you get the idea. The bigger the blend of white noise, the whiter the noise.