Spot on LJ!
Palaeloclimatology is an absolutely fascinating subject and while there's no denying that the earth has warmed over the past 70 years or so there's still a lot of work to be done to work out why and what the future holds.
A Hampshire airfield's met station was moved a few years ago and the surroundings were different from the original location. No comparison was made over any length of time to work out what the effect on temperature, wind, rainfall was but the Station still claims to have weather records dating back 60 odd years. No doubt the effect of moving the instruments was small but there was no attempt to quantify it (care to comment Langley Baston?). Clearly alterations of the surroundings of many long-established stations will have had an impact on their readings...the so heat-island effect but also change of use of agricultural land are examples.
A further thought is that the Carboniferous period of geological history was was one of the warmest and yet the amount of carbon dioxide in the atmosphere was negligible.
Finally it looks as though ice ages commence with global temperature falls of about 10 degrees in the space of a few decades. I'm not saying it will happen but that would certainly make your eyes water!!