One of the major problems with temperature measurement is that the area surrounding the thermometers gets built up over time. A Stevenson Screen at a small country airport with suffer as the airport gets paved with blacktop and air conditioners get installed in the terminal. Here is one perfect example of an official temperature measurement station at Picacho Peak State Park in Arizona.
From Watts Up With That:
How not to measure temperature (or climate change) #96
From the “global warming data looks better with heat-sinks and air conditioners” department.
Dr. Mark Albright, of the University of Washington writes:
Here is a great example of how NOT to measure the climate! On our way back to Tucson from Phoenix on Monday we stopped by to see the Picacho 8 SE coop site at Picacho Peak State Park. Note the white MMTS temperature monitor 1/3 of the way in from the left. The building is surrounded by the natural terrain of the Sonoran Desert, but instead the worst possible site adjacent to the paved road and SW facing brick wall was chosen in 2009 as the location to monitor temperature.
Here is a view looking Northeast:
Anthony posts a bunch of pictures, here are two of them. The sensor is in the small box on a pole.
Note the air conditioning compressors about ten feet away. No wonder this sensor is showing an increase in temperature. The satellite air temperature is the most accurate and unbiased measurement for the last 30 years and for the last 18 years, it has been showing cooling.