Background
The authors write that while some scientists have claimed that meteorological station air temperature records "are not sensitive to urbanization or that the effects are not quite significant compared with the overall trend of global warming, others believe such urban-related warming plays a significant role in these records," citing, in this regard, the studies of Landsberg (1981), Kukla et al. (1986), Karl et al. (1988), Changnon (1992) and Gallo et al. (1993).

What was done
"With the support of historical remote sensing data," in the words of He et al.," they say they "examined the impacts of urban expansion on the trends of air temperature at 69 meteorological stations in Beijing, Tianjin, and Hebei Province over the last three decades."

What was learned
The four Chinese researchers determined that urban-induced warming contributed an average of 44% to the total mean warming of the studied stations due to the various degrees of urbanization around each station, and that the natural climate warming calculated in this study was 0.30°C per decade for the last three decades. And they report that they also found that "the urbanization rate affected the trend of temperature to a large extent," noting that "10% additional increases in the urban areas around meteorological stations within 1 km will likely lead to 0.13°C increases in the temperature trend."

What it means
In their parting words of wisdom to us, He et al. write that "urban expansion may not have major impacts on the regional climate, but it may contribute to strong Urban Heat Island signals in meteorological records at the local scale, likely leading to a misinterpretation of overall warming magnitudes and even trends at the regional and global scales."

References
Changnon, S.A. 1992. Inadvertent weather-modification in urban areas - Lessons for global climate change. Bulletin of the American Meteorological Society 73: 619-627.

Gallo, K.P., McNab, A.L., Karl, T.R., Brown, J.F. and Hood, J.J. 1993. The use of NOAA AVHRR data for assessment of the urban heat-island effect. Journal of Applied Meteorology 32: 899-908.

Karl, T.R., Diaz, H.F. and Kukla, G. 1988. Urbanization: Its detection and effect in the United States climate record. Journal of Climate 1: 1099-1123.

Kukla, G., Gavin, J. and Karl, T.R. 1986. Urban warming. Journal of Climate and Applied Meteorology 25: 1265-1270.

Landsberg, H. 1981. The Urban Climate. Academic Press, New York, New York, USA.