Last night I posted the 2000-2008 temperature comparison of two Minnesota towns, Montevideo and Milan which are only 16 miles apart. A friend today commented that the bias was entirely negative and he wondered if a lake near Milan was the cause. I don't think that is the case. Why? Because the seasonality is seen in the years 1968 to 1975 and the overall bias is above zero. Below is the daily temperature difference between the two towns with a 180-day running average applied.
The amount of temperature difference seen in the 180-day average is very large, 2.5 deg F. Some of the individual days have more than 10 degree F differences. Clearly the raw data is highly inaccurate and yet this kind of terrible data is being used to scare you into being worried about the world overheating.
Whatever one wants to believe, with this data no one can know if the world has warmed or not.