We would like to thank Tobias Rothenberger for alerting us to this paper! Huang S, Taniguchi M, Yamano M, Wang CH, 2008: Detecting urbanization effects on surface and subsurface thermal environment - A case study of Osaka. Sci Total Environ, doi:10.1016/j.scitotenv.2008.04.019
The abstract reads
“Tremendous efforts have been devoted to improve our understanding of the anthropogenic effects on the atmospheric temperature change. In comparison, little has been done in the study of the human impacts on the subsurface thermal environment. The objective of this study is to analyze surface air temperature records and borehole subsurface temperature records for a better understanding of the urban heat island effects across the ground surface. The annual surface air temperature time series from six meteorological stations and six deep borehole temperature profiles of high qualities show that Osaka has been undergoing excess warming since late 19th century. The mean warming rate in Osaka surface air temperature is about 2.0 °C/100a over the period from 1883 to 2006, at least half of which can be attributed to the urban heat island effects. However, this surface air temperature warming is not as strong as the ground warming recorded in the subsurface temperature profiles. The surface temperature anomaly from the Osaka meteorological record can only account for part of the temperature anomaly recorded in the borehole temperature profiles. Surface air temperature is conventionally measured around1.5 m above the ground; whereas borehole temperatures are measured from rocks in the subsurface. Heat conduction in the subsurface is much less efficient than the heat convection of the air above the ground surface. Therefore, the anthropogenic thermal impacts on the subsurface can be more persistent and profound than the impacts on the atmosphere. This study suggests that the surface air temperature records alone might underestimate the full extent of urban heat island effects on the subsurface environment.”
The paper includes the text
“The Osaka station shows a warming trend of 1.99 °C/100a over the 124 year period from 1883 to 2006, more than triple the 20th century global warming rate 0.6 °C/100a (IPCC, 2001). The anomalous urban warming is consistently recorded in the
records from the nearby urban/suburban stations, of which the warming rates are 2.24 °C/100a for Kyoto, 1.45 °C/100a for Kobe, and 1.96 °C/100a for Nara, respectively. In comparison, the warming rates recorded in the two rural stations are more diverse. Over its 55-year life span, the Tsurugisan station showed a warming rate of 0.47 °C/100a which is slightly lower than the global average; whereas the 82-year Ibukiyama record showed a 1.60 °C/100a warming rate that is much greater than the global average.”
and
“The JMA (JMA, 2006) cautions that its regional estimate might be not entirely free of urbanization perturbation. Based on the records from the urban stations around Osaka and the JMA regional estimate, a conservative estimate of the urban heat island effects in Osaka would be in the range of 1–2 °C/ 100a. This estimate agrees in general with the early analysis of Kato (1996). Based on principal component score analysis of monthly mean temperature data for the period from 1920 to 1992 from 51 meteorological stations in Japan, Kato suggests that the maximum urban effects with a population of over 100,000 in 1993 were 1.0–2.5 °C/100a in Japan (Kato, 1996).”
What this paper communicates is that monitoring temperature at just one site and/or one level is an inadequate diagnostic of the role of urban areas in altering the heating that occurs due to this landscape change. This study also documents the variations in time of the urban and rural temperature changes, as well as the spatial heterogeniety of these trends. Claims by papers such as
Peterson, T. C., 2003: Assessment of urban versus rural in situ surface temperatures in the contiguous United States: No difference found. J. Climate, 16, 2941–2959,
and
Parker, D. E. (2004), Climate: Large-scale warming is not urban, Nature, 432, 290(18 November 2004); doi:10.1038/432290a.
are inconsistent with the observations reported in the new Huang et al paper.