There is a burgeoning grass roots movement (described here, in part) to better document key temperature measurement stations both to better correct past measurements as well as to better understand the quality of the measurements we are getting.
Steve McIntyre has had some back and forth conversations with Eli Rabbett about temperature measurement points, each accusing the other of cherry-picking their examples of bad and good installations. McIntyre therefore digs into one of the example temperature measurement points Rabbett offers as a cherry-picked example of a good measurement point. For this cherry-picked good example of a historical temperature measurement point, here are the adjustments that are made to this site's measurements before it is crunched up into the official historic global warming numbers:
Corrections have been made for:
- relocation combined with a transition of large open hut to a wooden Stevenson screen (September 1950) [ed: This correction was about 1°C]
- relocation of the Stevenson screen (August 1951).
- lowering of Stevenson screen from 2.2 m to 1.5 m (June 1961).
- transition of artificial ventilated Stevenson screen to the current KNMI round-plated screen (June 1993).
- warming trend of 0.11°C per century caused by urban warming.
Note that these corrections, which are by their nature guesstimates, add up to well over 1 degree C, and therefore are larger in magnitude than the global warming that scientists are trying to measure. In other words, the noise is larger than the signal.
Postscript: 0.11C per century is arguably way too low an estimate for urban warming.