Mankind has been able to measure temperature with some degree of precision for less than 3 centuries. And we have had something like a functioning worldwide network of weather stations for a century or less. So when Warmistas claim a long-term warming rate of .X degrees per time period, we do not have the temperature database on which such predictions can be made.
Climate cycles, however, can be observed through all sorts of forensic evidence - tree rings, moraine locations, pollen in core samples from lake beds, etc. - and written sources and records. Approximate temperature ranges can be inferred, but not precisely enough to be a database on which Warmistas can make the fine-resolution claims they make.
