There is another excellent paper which documents the significant role of local human activites on the long termperature trends, as well as challenges the development of grid averaged temperatures using the observed large heterogeniety of the surface temperature observations [Thanks to Geoff Smith for altering us to this paper!].
The paper is
Lai, L.-W., and W.-L.Cheng 2009: Air temperature change due to human activities in Taiwan for the past century. Int. J. Climatology, 10.1002/joc.1898.
The abstract reads
“The purpose of this study was to statistically examine air temperature change and to analyse the anthropogenic factors potentially influencing air temperature changes in Taiwan for the period 1897-2005 using homogenized temperature measurement time series. In this study, the standard normal homogeneity test was used to attain homogeneity of all air temperature series. To analyse air temperature data from 1897 to 2005, a time-series regression model and a product-moment correlation were used. The annual mean maximum temperatures (Tmax), annual mean minimum temperatures (Tmin) and the number of days in which the air temperature 30°C increased significantly in most regions in Taiwan, and the rate of increase for Tmin was higher than that of Tmax. In other words, in the past century the night temperatures have become higher and the period of hot days in Taiwan have become longer. However, over the past century and before 1962, the trend of Tmax in central Taiwan (i.e. Jihyuehtan and Taichung) decreased significantly, which is inconsistent with greenhouse gas warming and general warming observed in other sites in Taiwan. Furthermore, during the economic growth experienced between 1962 and 2005, the rates of increase for Tmax and Tmin in major cities with similar climate conditions (i.e. Tainan and Kaohsiung) were significantly different, as were the correlation coefficients between temperature changes and the number of various economic sectors in the cities. The results of these statistical analyses suggest that human activities strongly affected air temperature changes in these urban areas. The obvious lack of spatial homogeneity indicates that various non-greenhouse gas processes have played roles in climate change in Taiwan, and these factors must be considered when analysing long-term air temperature variations. Caution should be exercised when using grid data to assess temperature trends at the grid-box level.”
The conclusions include the text
”In conclusion, the results from this study strongly suggest that, during Taiwan’s ‘economic boom period’, its rapid expansion in terms of population and economic activities influenced air temperature changes directly (i.e. emitting GHGs and generating anthropogenic heating) and indirectly (i.e. changing the urban landscape, such as the depth of street canyons; the H/W ratio; proximity to the sea; vegetation space; SVF and heat capacity).”
Their statement that
“The obvious lack of spatial homogeneity indicates that various non-greenhouse gas processes have played roles in climate change in Taiwan, and these factors must be considered when analysing long-term air temperature variations. Caution should be exercised when using grid data to assess temperature trends at the grid-box level”
raises questions about the robustness of the homogenization of the surface temperature trend record, as we also raised in our paper
Pielke Sr., R.A. J. Nielsen-Gammon, C. Davey, J. Angel, O. Bliss, N. Doesken, M. Cai., S. Fall, D. Niyogi, K. Gallo, R. Hale, K.G. Hubbard, X. Lin, H. Li, and S. Raman, 2007: Documentation of uncertainties and biases associated with surface temperature measurement sites for climate change assessment. Bull. Amer. Meteor. Soc., 88:6, 913-928.
where we stated in our abstract that
“The use of temperature data from poorly sited stations can lead to a false sense of confidence in the robustness of multidecadal surface air temperature trend assessments.”