A CA reader has brought to our attention an interesting new article by Pielke Sr et al, Unresolved Issues with the Assessment of Multi-Decadal Global Land-Surface Temperature Trends, which disucsses microsite problems. There is a lengthy roster of co-authors: Roger A. Pielke Sr., Christopher A. Davey, Dev Niyogi, Souleymane Fall, and Jesse Steinweg-Woods, Ken Hubbard and Xiaomao Lin, Ming Cai, Young-Kwon Lim, Hong Li, John Nielsen-Gammon, Kevin Gallo, Robert Hale, Rezaul Mahmood and Stuart Foster, Richard T. McNider, Peter Blanken. (Note: also see discussion at Pielke Sr blog here )
The integrity of climatological observations is often compromised by poor environmental exposure of instruments. Examples of poor exposure are provided by three United States HCN (USHCN) sites in Kentucky (see figures for Greensburg  (Figure 5), Leitchfield_2_N  Figure 6), and Hopkinsville  (Figure 7). In each case, a combination of anthropogenic (e.g., asphalt and concrete surfaces, buildings) and natural features (e.g., trees and shrubs, slopes) of the microscale environment create forcings that are not representative of the larger mesoscale environment.
Below is their Figure 7, shows another site, which is in grotesque non-compliance with WMo standards. Note what appears to be a barbecue conveniently located below the temperature sensor. So the problems are not limited to northern California. Obviously Karl and Hansen have not performed the most minimal due diligence to ensure that the USHCN sites that they rely on meet the WMO standards that they presume.
The article mentions Peterson 2006, which apparently says that these grotesque problems don’t “matter” and a response from Pielke et al 2007, which says that they do. .
Peterson  concluded that any biases associated with the poor siting in eastern Colorado, when adjusted, did not affect estimates of regional temperature trends. However, in a response to the Peterson article, Pielke et al.  pointed out several issues which Peterson did not adequately investigate, including often undocumented station changes, ignored uncertainties in the adjustments, and land-use/land-cover change issues associated with climate station adjustments.
The PEterson reference is: Peterson, T.C., Examination of potential biases in air temperature caused by poor station locations. Bull. Amer. Meteor. Soc., 87, 1073-1089. 2006.