Anthony Watts reports an interesting survey of raw temprature data in rural and urban locations in the U.S.
The raw data shows what many have suspected for a long time, that urbanisation contributes a lot to observed warming.
The paper's author, Dr Edward Long, then compares the same data set but in its "adjusted" format. Climate scientists often adjust the data to try to compensate for effects such as changes of station location and obviously for urbanisation. That's fair enough if you are objective and trying to find the truth- a little bit more problematic if you are already committed to a particular result and are trying to confirm your belief.
Here are the "adjusted" data
Suddenly you can see global warming! It's clear that the rural data have been adjusted to match the increase in the urban data, when it should have been the other way around. Furthermore the adjustments have been done in such a way as to emphasise an apparent warming trend and not in a neutral way.
The paper’s summary reads:
Both raw and adjusted data from the NCDC has been examined for a selected Contiguous U. S. set of rural and urban stations, 48 each or one per State. The raw data provides 0.13 and 0.79 oC/century temperature increase for the rural and urban environments. The adjusted data provides 0.64 and 0.77 oC/century respectively. The rates for the raw data appear to correspond to the historical change of rural and urban U. S. populations and indicate warming is due to urban warming. Comparison of the adjusted data for the rural set to that of the raw data shows a systematic treatment that causes the rural adjusted set’s temperature rate of increase to be 5-fold more than that of the raw data. The adjusted urban data set’s and raw urban data set’s rates of temperature increase are the same. This suggests the consequence of the NCDC’s protocol for adjusting the data is to cause historical data to take on the time-line characteristics of urban data. The consequence intended or not, is to report a false rate of temperature increase for the Contiguous U. S.
The full paper may be found here: Contiguous U.S. Temperature Trends Using NCDC Raw and Adjusted Data for One-Per-State Rural and Urban Station Sets (PDF) and is freely available for viewing and distribution.