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The Industrial-Region Heat Island Effect
De Laat, A.T.J. and Maurellis, A.N. 2004. Industrial CO2 emissions as a proxy for anthropogenic influence on lower tropospheric temperature trends. Geophysical Research Letters 31: 10.1029/2003GL019024.

What was done
Using a global data set developed by Van Aardenne et al. (2001), which reveals the spatial distribution of various levels of industrial activity over the planet, as quantified by the intensity of anthropogenic CO2 emissions, the authors divided the surface of the earth into non-industrial and industrial sectors of various intensity levels, after which they plotted the 1979-2001 temperature trends (C/decade) of the different sectors using data from both the surface and the lower and middle troposphere.

What was learned
De Laat and Maurellis report that "measurements of surface and lower tropospheric temperature change give a very different picture from climate model predictions and show strong observational evidence that the degree of industrialization is correlated with surface temperature increases as well as lower tropospheric temperature changes." Specifically, they find that the surface and lower tropospheric warming trends of all industrial regions are greater than the mean warming trend of the earth's non-industrial regions, and that the difference in warming rate between the two types of land-use grows ever larger as the degree of industrialization increases.

What it means
The authors say that "areas with larger temperature trends (corresponding to higher CO2 emissions) cover a considerable part of the globe," which implies that "the 'real' global mean surface temperature trend is very likely to be considerably smaller than the temperature trend in the CRU [Hadley Center/Climate Research Unit] data," since the temperature measurements that comprise that data base "are often conducted in the vicinity of human (industrial) activity." These findings, in their words, "suggest a hitherto-overlooked driver of local surface temperature increases, which is linked to the degree of industrialization" and "lends strong support to other indications that surface processes (possibly changes in land-use or the urban heat effect) are crucial players in observed surface temperature changes (Kalnay and Cai, 2003; Gallo et al., 1996, 1999)." Hence, they conclude that "the observed surface temperature changes might be a result of local surface heating processes and not related to radiative greenhouse gas forcing." We concur, believing that the evidence for this proposition is so strong that the words "might be" in the preceding sentence could actually be replaced with "are."

Gallo, K.P., Easterling, D.R. and Peterson, T.C. 1996. The influence of land use/land cover on climatological values of the diurnal temperature range. Journal of Climate 9: 2941-2944.

Gallo, K.P., Owen, T.W., Easterling, D.R. and Jameson, P.F. 1999. Temperature trends of the historical climatology network based on satellite-designated land use/land cover. Journal of Climate 12: 1344-1348.

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

Van Aardenne, J.A., Dentener, F.J., Olivier, J.G.J., Klein Goldewijk, C.G.M. and Lelieveld, J. 2001. A 1 x 1 resolution data set of historical anthropogenic trace gas emissions for the period 1890-1990. Global Biogeochemical Cycles 15: 909-928.

Reviewed 9 June 2004