The problem Hill, is that the empirical data is flawed. A data collection point 100 years ago was in a farmers field and now that same station is surrounded by concrete and asphalt in an urban heat island. And remember climate-gate two when up to 60 percent of the collection points in Siberia were deleted because they showed no warming. Somewhere between 4500 to 7500 years before present, there was a long period of very hot weather on the northern great plains in America. We know this due to the lack of stone tools that delineate that period. The game animals migrated north. No game animals = no stone tools. But I guess Bush probably caused that.