Anthony Watts has claimed that the measured temperature record has shown an upward rise in temperatures because large number of weather stations have been dropped from the record and that adjustments to temperature data have been made to generate the rise.
These are serious claims demonstrating either gross incompetence or serious outright scientific fraud, either claim if true would call into question the reliability NASA’s giss temperature series.
The first of these claims had also been made in a paper published by Ross McKitrick from the Department of Economics at the University of Guelph in 2003. Tim Lambert responded to McKitrick’s claims in 2004 here demonstrating that after adjusting for the appropriate weighting of the weather stations the impact due to the reduction in the number of weather stations is much smaller than McKitrick stated. Even so, Hansen in 1999 was aware of the issue and had accounted for the impact of the reduction in the number of weather stations whilst doing his temperature reconstruction.
Anthony Watts setup the website surfacestations.org the purpose for which was to rate all the US weather stations and create a public record of that rating. This rating was based on the location of the weather station, whether it was located appropriately or not, for example in an asphalt car park, or near a building, or close to an air conditioning unit or whether it was in the middle of a field. Menne et. al. (Discussed at climate progress) used the ratings at surfacestations.org and found that automated stations were rated poorly compared to the manual stations, that the automated stations underestimated the temperature because of the temperature sensor used rather than as Anthony Watts suggested overestimated the temperature due to Urban Heat Island affects or being near the output of an air conditioning units.
This first claim was clearly was not enough for Anthony Watts, who also added the claim that it is the adjustments to the temperatures at various weather stations that are the reason for the rise in the measured temperatures.
Tamino gets into the act and breaks down the temperature record into two records, one temperature series is the continuous one including only those weather stations still included in the current temperature series, and the other is made up of all the other weather stations. First up Tamino shows that the temperature rise in the complete temperature series is less than the temperature rise in the series which stops in the early nineties.
Tamino's Global Temperature Analysis
Tamino’s analysis was then repeated independently by others, one of whom also went on to compare the results with the NASA GISS temperature series here.
The weather stations were not removed from the temperature series. What happens is that only the automated weather stations have their data updated with the appropriate meteorological offices in anything close to real time, the data from the non automated stations is supplied at a later date. Weather stations were not selected to be removed from the temperature series on any other basis other than whether they are automated weather stations or not.
What Tamino’s and others analysis shows is that the removal of the non automated weather stations has not resulted in an artificial increase in the warming trend shown in NASA’s GISSTemp but instead leaves open the possibility that GISSTemp is underestimating the global warming temperature trend.