In my post on the Mohonk Weather Station, the question came up about “raw” temperature data. Tom in Texas complained that he’d looked at data from the observer B91 forms and that it didn’t match what was posted in published data sets.
Neither NOAA nor NASA serve weather station data “raw”.
We’ve all seen examples posted here of how GISS adjusts data. But, it is not only NASA GISS that does this practice, in fact, NOAA adjusts temperature data also, and it is by their own admission. For example here is a NOAA provided graphs showing the trend over time of all the adjustments they apply to the entire USHCN dataset.
As illustrated in the graphs above, in simplest terms NOAA adds a positive bias to the raw data reported by weather station observers with their own “adjustment” methodology.
It is important to note that the graph on the bottom shows a positive adjustment of 0.5°F spanning from 1940 to 1999. The agreed upon “global warming signal” is said to be 1.3°F (.74C) over the last century.
The NOAA source for these graphs is: http://cdiac.ornl.gov/epubs/ndp/ushcn/ndp019.html