sierra, you need to appreciate that there are no direct temperature measurements prior to "modern man". All such readings are done via proxies, such as ice cores. A more general view of historical temperatures can be found via other means. For example the river Thames froze over a number of times some 150 years ago or more. Yes, these are localised events but they give a good indication of at least the regional climate.
As for historical temperatures obtained from ice cores, here a link. There are many others.
