AFLM,

Thermometer data is not particularly useful as you point out. That is why very few models use that data. There is a tremendous amount of "proxy" information available and that is what scientists are using. If you really have an interest in the science I would recommend starting with "Climate since A.D. 1500" by Bradley and Jones (Routledge, ISBN 0-415-12030-6). It has excellent descriptions of many of these techniques and the data that has been obtained from them. Many of the same techniques and others as well have been used to retrieve information for several hundred thousand years in the past.

Respectfully,

Jerry