Let's suppose that you're right, and it can be ascertained what the CO2 levels were 500 years ago. How, pray tell, are you going to get the temperature data?
OK, I'm not an expert but my understanding is that prior to 1850 we must rely upon proxies for temperature data, which I know you're not happy with (see below). I also agree with your supposition that a conventional bulb thermometer probably isn't the most accurate device with which to record temperature.
All of this is beside my point which is that we've vastly more carbon dioxide in our atmosphere now than in all of our history on Earth as Homo Sapiens Sapiens. We know what greenhouse gases do to the climate and we know there's a degree of time-lag between cause and effect. Whilst I agree that getting accurate temp measurements is important, when we have such clear readings for CO2 levels your argument sounds like you don't believe Rome burned down because nobody recorded the name of the tune Nero was playing on his fiddle at the time. Ugh, it's late and my metaphor-fu is weak right now.
I don't need to provide you any competing data. This author relies upon the growth of tree rings and depositions of sediment to infer what temperatures were. You show me how his methods of gathering data are reliable, and perhaps I'll be persuaded by you.
As mentioned before we must rely on proxies as we were obviously not present millions of years in the past to record the actual temperature. If you have a problem with this method of analysis you may well be right but you're going to need to do better than 'I feel it's unreliable' to convince me there's a real issue. I asked for facts in my last post and you tell me you don't need to provide any - there's precious little room for debate if you won't enumerate your concerns.
You employ a classic trick of shifting the burden of proof.
I'm sorry you feel I am engaging in tricks or subterfuge to debate you, I thought I was just pursuing your line of discussion, honestly. I've no agenda besides a desire for the truth, however pretty or ugly.
The burden of proof is on the author of the study, not upon me to prove him wrong. He must persuade his audience, not the other way around.
Except that it is you yourself who is making extraordinary claims, as proxies are a well understood and commonly-employed scientific tool for measurement. What evidence do you have that these proxies are flawed and unsuitable for use in the models we're discussing?