It's well-known that tree ring data is extremely difficult to analyze because so many factors influence tree ring width. There are entire papers and books on dendrochronology. Nevertheless, the data matches the instrumental temperature record quite well for about 75% of the record.
Yes, this is exactly the problem. Annual grows of a tree is affected by rainfall, temperature, nutrient availability, CO2 concentration, who knows what else. Every tree resides in its own local micro environment, soil topology, underground water profile, the growth depend on which side of mountain valley the tree is, etc. For each individual tree and each particular year, all these factors are mathematically convoluted into a single number, ring thickness. More, the growth is likely dependent on individual shape of a season, was it slow spring and hot summer, or early spring and mild summer, and whatever winter. All possible combination would likely result in different ring size, yet the average season temperature could be exactly the same. Alternatively, temperatures might be changing, but so might be a change in water supply, so the ring would have the same thickness. All these parameters are convoluted, and without exact data about all other factors it is IMPOSSIBLE to invert tree ring data into temperatures. For any normal scientist who made an effort to look into this mess, it is obvious that the dendroclimatology is a pseudoscience, junk science. It is not just "extremely difficult to analyze", it is utter nonsense. It is obvious that the result 200% depends on selection of samples, and anyone can get any result out of this NOISE depending on their agenda, as it was demonstrated by materials from ClimateGate.
My interpretation of your 75/25% number is that even after careful targeted selection of data, 25% still do not fit into preconceived AGW theory.
Where do you get 1960-70? The main divergence is after 1980
I got my number from the CRU code, posted above. It says 1960. Are you saying that your "divergence" explanation is bogus as well?
No that's simply wrong. Mann et al. 2008
(the revised, updated "hockey stick", if you prefer) concluded
Why would anyone refer to "conclusions" of this guy after all this ClimateGate exposure is above any comprehension. Is this a mockery, or what?
You need to realize that entire paleoclimatology is a completely speculative field, from which no quantitative projection or "policy making" conclusion on any changes is possible, especially when a comparision with instrumental records is attempted.