We have stated in the literature that photographic documentation of the observing site that are part of the global land surface temperature assessments is critically important, as we have identified poor instrument exposure with respect to the assessment of long term temperature trends; e.g. see
Pielke Sr., R.A., C. Davey, D. Niyogi, K. Hubbard, X. Lin, M. Cai, Y.-K. Lim, H. Li, J. Nielsen-Gammon, K. Gallo, R. Hale, J. Angel, R. Mahmood, S. Foster, J. Steinweg-Woods, R. Boyles , S. Fall, R.T. McNider, and P. Blanken, 2006: Unresolved issues with the assessment of multi-decadal global land surface temperature trends. J. Geophys. Research, submitted.
The National Climate Data Center (NCDC) has started a compilation of these photographs as part of the USA contribution to GCOS (Global Climate Observing System). As part of this effort a set of photographs have been archived (see).
I have selected a sample of them from that website (others can be obtained from their website). The Mexican photographs, in particular, are effective presentations which follow the format that we used in
Davey, C.A., and R.A. Pielke Sr., 2005: Microclimate exposures of surface-based weather stations – implications for the assessment of long-term temperature trends. Bull. Amer. Meteor. Soc., Vol. 86, No. 4, 497–504.
It is clear from the examples of the land surface temperature observation sites, that most are not appropriately sited to detect tenths of degrees of temperature changes per decade since their microclimate clearly is not likely to be stationary in time. Moreover, several sites are on rooftops.
Thus, while the temperature data certainly are very valuable for weather analysis, their use in the construction of a global surface land surface temperature trend is not appropriate. Peterson has claimed in
Peterson, T.C., 2006. Examination of potential biases in air temperature caused by poor station locations. Bull. Amer. Meteor. Soc., 87, 1073-1089.
that he can adjust poorly sited stations of this type, however, as we show in our response article to his paper,
Pielke Sr., R.A, J. Nielsen-Gammon, C. Davey, J. Angel, O. Bliss, M. Cai, N. Doesken, S. Fall, K. Gallo, R. Hale, K.G. Hubbard, H. Li, X. Lin, , D. Niyogi, and S. Raman, 2006: Documentation of bias associated with surface temperature measurement sites. Bull. Amer. Meteor. Soc., submitted.
no value is added from such sites. In addition, for locations where these poorly sited locations are the only data used to construct a grid area average in the global temperature trend data base, their use will introduce spatially unrepresentative data into the analyses.
Examples of the photographs are available from the following:
Clearly, the exposure to nearby buildings, parking lots and other local structures makes the use of these locations to detect tenths of a degree per decade in surface temperature trends inappropriate.