Former TV weatherman Anthony Watts has been engaged in an ongoing attack on the reliability of the US network of surface weather stations, claiming that poor placement of the stations has resulted in data that’s biased toward the warm side. Watts set up the website SurfaceStations.org to coordinate photographic evidence of problem stations, and many climatologists have applauded Watts for demonstrating the need to improve the nation’s weather monitoring system.

Typical problems identified at SurfaceStations.org include stations situated near the exhaust of air conditioning units, in asphalt parking lots, and on hot rooftops.

But is Watts correct when he claims that problems with the stations caused a warm bias? Jeff Masters of Wunder Blog reports on a new study from the National Climatic Data Center concluding that the problems identified by Watts and his investigators are real, all right — but that the badly situated stations tend to have a bias toward cooler temperatures: Poorly sited U.S. temperature instruments not responsible for artificial warming.

While Watts’ publication by the Heartland Institute is a valuable source of information on siting problems of the U.S. network of weather stations, the publication did not undergo peer-review—the process whereby three anonymous scientists who are experts in the field review a manuscript submitted for publication, and offer criticisms on the scientific validity of the results, resulting in revisions to the original paper or outright rejection. The Heartland Institute is an advocacy organization that accepts money from corporate benefactors such as the tobacco industry and fossil fuel industry, and publishes non-peer reviewed science that inevitably supports the interests of the groups paying for the studies. Watts did not actually analyze the data to see if taking out the poorly sited surface stations would have a significant impact on the observed 1.1°F increase in U.S. temperatures over the past century. His study would never have been publishable in a peer-reviewed scientific journal.

Fortunately, a proper analysis of the impact of these poorly-sited surface stations on the U.S. historical temperature record has now been done by Dr. Matthew Menne and co-authors at NOAA’s National Climatic Data Center (NCDC). In a talk at last week’s 90th Annual Meeting of the American Meteorological Society, Dr. Menne reported the results of their new paper just accepted for publication in the Journal of Geophysical Research titled, On the reliability of the U.S. Surface Temperature Record [PDF]. Dr. Menne’s study split the U.S. surface stations into two categories: good (rating 1 or 2) and bad (ratings 3, 4 or 5). They performed the analysis using both the rating provided by surfacestations.org, and from an independent rating provided by NOAA personnel. In general, the NOAA-provided ratings coincided with the ratings given by surfacestations.org. Of the NOAA-rated stations, only 71 stations fell into the “good” siting category, while 454 fell into the “bad” category. According to the authors, though, “the sites with good exposure, though small in number, are reasonably well distributed across the country and, as shown by Vose and Menne [2004], are of sufficient density to obtain a robust estimate of the CONUS average”. Dr. Menne’s study computed the average daily minimum and maximum temperatures from the good sites and poor sites. The results were surprising. While the poor sites had a slightly warmer average minimum temperature than the good sites (by 0.03°C), the average maximum temperature measured at the poor sites was significantly cooler (by 0.14°C) than the good sites. As a result, overall average temperatures measured at the poor sites were cooler than the good sites. This is the opposite of the conclusion reached by Anthony Watts in his 2009 Heartland Institute publication.

Figure 2. Annual average maximum and minimum unadjusted temperature change calculated using (c) maximum and (d) minimum temperatures from good and poor exposure sites (Menne 2010). Poor sites showed a cooler maximum temperature compared to good sites. For minimum temperature, the poor sites were slightly warmer. The net effect was a cool bias in poorly sited stations. The dashed lines are for stations ranked by NOAA, while the solid lines are for the stations ranked by surfacestations.org.

Andrew Revkin has more, including comments from Anthony Watts: On Weather Stations and Climate Trends.