Pielke R. A. Sr., et al. (2007), Unresolved issues with the assessment of multidecadal global land surface temperature trends, J. Geophys. Res., 112, D24S08, doi:10.1029/2006JD008229 [also available from http://www.climatesci.org/publications/pdf/R-321.pdf]
has appeared. This paper can help explain the role of non-spatially representative measurements of multi-decadal land surface air temperature trends, that was extracted statistically in the article
McKitrick, R.R. and P.J. Michaels (2007), Quantifying the influence of anthropogenic surface processes and inhomogeneities on gridded global climate data, J. Geophys. Res., 112, D24S09, doi:10.1029/2007JD008465
The abstract of the Pielke et al paper reads
“This paper documents various unresolved issues in using surface temperature trends as a metric for assessing global and regional climate change. A series of examples ranging from errors caused by temperature measurements at a monitoring station to the undocumented biases in the regionally and globally averaged time series are provided. The issues are poorly understood or documented and relate to micrometeorological impacts due to warm bias in nighttime minimum temperatures, poor siting of the instrumentation, effect of winds as well as surface atmospheric water vapor content on temperature trends, the quantification of uncertainties in the homogenization of surface temperature data, and the influence of land use/land cover (LULC) change on surface temperature trends. Because of the issues presented in this paper related to the analysis of multidecadal surface temperature we recommend that greater, more complete documentation and quantification of these issues be required for all observation stations that are intended to be used in such assessments. This is necessary for confidence in the actual observations of surface temperature variability and long-term trends.”
The issues that we found and the type of bias in multi-decadal land surface air temperature trends that results, based on the Pielke Sr. et al. JGR paper are the following:
1. measurement of minimum temperature at just one level ( a significant warm bias when the nocturnal boundary layer is warming; a significant cold bias when the nocturnal boundary layer is cooling);
2. poor siting of the instrumentation (probably mostly a warm bias but needs further study; regardless the data is not spatially representative).
3. effect of multi-decadal trends in near surface absolute humidty (for the same multi-decadal trend in heat content, a drying trend results in a warm bias while a moistening trend results in a cool bias when surface air temperature trends are used by itself in the construction of land averages);
4. the quantification of uncertainties in the homogenization of surface temperature data (results in an uncertainty of an unknown magnitude, but appears to be significant; further study needed);
5. the influence of land-use/land-cover (LULC) change (primarily a warm bias, with some exceptions – such as when an arid region is irrigated);
6. the completion of the global analysis of multi-decadal surface air temperature trends by the different groups (NCDC, CRU, GISS) are not independent of each other, as they each draw raw data from essentially the same surface observation sites. Only their specific analysis routines are different.
We have identified a fundamental problem with the use of land surface air temperatures in the construction of a global average multi-decadal trend. The question is whether these temperatures are sufficiently coupled to the radiative and thermodynamic characteristics of the Earth system to construct a global average trend that can be diagnosed to obtain the radiative forcing of the climate system.
We conclude, that particularly for the minimum temperatures, it is not sufficiently coupled!
This analysis, as well as other studies such as the McKitrick and Michaels JGR paper, should be a wake up call that erroneous information is being communicated to policymakers and others on the actual radiative imbalance of the climate system. The 2007 IPCC ignored assesing these unresolved issues which, as a consequence, result in a warm bias in their conclusions on the magnitude of global warming.