On the reliability of the U.S. Surface Temperature Record
Matthew J. Menne*, Claude N. Williams, Jr., and Michael A. Palecki
(NOAA/National Climatic Data Center, Asheville, NC 28801, U.S.A.)
Given the now extensive documentation by surfacestations.org (Watts ) that the exposure characteristics of many USHCN stations are far from ideal, it is reasonable to question the role that poor exposure may have played in biasing CONUS temperature trends. However, our analysis and the earlier study by Peterson  illustrate the need for data analysis in establishing the role of station exposure characteristics on temperature trends no matter how compelling the circumstantial evidence of bias may be. In other words, photos and site surveys do not preclude the need for data analysis, and concerns over exposure must be evaluated in light of other changes in observation practice such as new instrumentation.
Indeed, our analysis does provide evidence of bias in poor exposure sites relative to good exposure sites; however, given the evidence provided by surfacestations.org that poor exposure sites are predominantly MMTS sites, this bias is consistent with previously documented changes associated with the widespread conversion to MMTS-type sensors in the USHCN. Moreover, the bias in unadjusted maximum temperature data from poor exposure sites relative to good exposure sites is, on average, negative while the bias in minimum temperatures is positive (though smaller in magnitude than the negative bias in maximum temperatures). The adjustments for instrument changes and station moves provided in version 2 of the USHCN monthly temperature data largely account for the impact of the MMTS transition, although an overall residual negative bias remains in the adjusted maximum temperature series. Still, the USHCN adjusted data averaged over the CONUS are well aligned with the averages derived from the USCRN for the past five years.
*Correspondence e-mail: MatthewMenne@noaa.gov
Accepted for publication in Journal of Geophysical Research - Atmospheres. Published 2010 American Geophysical Union. Further reproduction or electronic distribution is not permitted. Not subject to U.S. copyright.
Link to complete open-access paper: http://www1.ncdc.noaa.gov/pub/data/ushcn/v2/monthly/menne-etal2010.pdf