| The question isn't that the sites are/are not poorly situated; the question is "what impact does that have on overall average temperature readings?" Here's the most relevant paper http://pielkeclimatesci.files.wordpress.com/2011/05/r-3671.p... . It "surveyed 82.5% of the U.S. Historical Climatology Network (USHCN)", """Temperature trend estimates vary according to site classification, with poor siting leading to an overestimate of minimum temperature trends and an underestimate of maximum temperature trends, resulting in particular in a substantial difference in estimates of the diurnal temperature range trends. The opposite-signed differences of maximum and minimum temperature trends are similar in magnitude, so that the overall mean temperature trends are nearly identical across site classifications. Homogeneity adjustments tend to reduce trend differences, but statistically significant differences remain for all but average temperature trends.""" In other words, for purposes of determining average temperature trends - which is what we are talking about - the siting does not play a statistically significant role Note also that the numbers you gave ("Class 5 (CRN5) (error > 5C)") come from NOAA's Site Information Handbook where it clearly says "The errors for the different classes are estimated values." The results of that paper will no doubt help refine those estimates. Finally, I point to the difference in how "artificial heat source" is defined for purposes of that classification vs. how it's understood in general reading. Without knowing the technical definition, most people will assume that it's near an active heat source, like "an air conditioner exhaust". But "artificial heat source" also includes "parking lot, or concrete surface" which are passive heat sources. And as the paper shows, the result is that they moderate the temperature but do not significantly affect the overall average. |