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Recent Dramatic Growth of Urban Heat Islands in China
Zhou, L., Dickinson, R.E., Tian, Y., Fang, J., Li, Q., Kaufmann, R.K., Tucker, C.J. and Myneni, R.B. 2004. Evidence for a significant urbanization effect on climate in China. Proceedings of the National Academy of Sciences 101: 9540-9544.

Kalnay and Cai (2003) used differences between trends in observed surface air temperature in the continental United States and corresponding trends determined from a reanalysis of global weather over the past 50 years -- the NCEP-NCAR 50-year Reanalysis (NNR) project -- to estimate the impact of land-use changes on surface warming, which has historically been determined directly from surface air temperature measurements. The reanalysis-derived surface air temperatures, however, do not employ surface observations. Rather, they are based on atmospheric vertical soundings derived from both satellites and balloons, so that surface air temperatures are estimated from atmospheric values via this procedure. Over rural areas, both surface-derived and reanalysis-derived surface air temperature data sets were shown by the two scientists to yield essentially identical trends; and, therefore, they concluded they "could attribute the differences between monthly or annually averaged surface-temperature trends derived from observations and from the NNR primarily to urbanization and other changes in land use."

What was done
Zhou et al. employ an improved version of this first reanalysis approach (R-1) -- which includes "newer physics and observed soil moisture forcing," the fixing of "known errors of R-1," and a more accurate characterization of clouds -- to determine the impacts of land-use changes on surface air temperature throughout southeast China, where rapid urbanization has occurred over the last quarter-century, calling their new-and-improved second reanalysis approach R-2.

What was learned
The group of eight scientists derived an "estimated warming of mean surface [air] temperature of 0.05C per decade attributable to urbanization," which they say "is much larger than previous estimates for other periods and locations, including the estimate of 0.027C for the continental U.S. (Kalnay and Cai, 2003)." They note, however, that because their analysis "is from the winter season over a period of rapid urbanization and for a country with a much higher population density, we expect our results to give higher values than those estimated in other locations and over longer periods."

What it means
The findings of this study, which the authors describe as "illustrative rather than definitive," are nevertheless indicative of the very high likelihood that significant urban-growth-induced warming permeates much of the surface air temperature record that is claimed by the IPCC and Mann et al. (1998,1999) to represent mean global background conditions, and which portrays dramatic warming over the period of time pertaining to the study of Zhou et al., i.e., January 1979 to December 1998. Hence, it is also very likely that the global warming of the past quarter-century or so is much more likely to be of the "run-of-the-mill" variety than "unprecedented," as is typically claimed by climate alarmists.

Kalnay, E. and Cai, M. 2003. Impact of urbanization and land-use change on climate. Nature 423: 528-531.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1998. Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K. 1999. Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters 26: 759-762.

Reviewed 21 July 2004