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Urban Warming With No Change in Population
Reference
Bohm, R. 1998. Urban bias in temperature time series - A case study for the city of Vienna, Austria. Climatic Change 38: 113-128.

What was done
The author made use of nine urban, suburban and rural temperature records (three of each type, selected as best on the basis of careful study from a total of 34 available records) to determine the evolving nature of the heat island of Vienna, Austria between 1951 and 1996, a 45-year period over which the city experienced zero population growth. Simultaneously, however, there was a 20% decrease in woodland and a 30% decrease in grassland within the city, as well as a doubling of the number of buildings, a ten-fold increase in the number of cars, a 60% increase in street, pavement and parking area, and a 2.5-fold increase in energy consumption.

What was learned
The suburban stations exhibited city-induced temperature increases ranging from 0.11 to 0.21C over the 45-year period of the study, while the urban stations experienced city-induced temperature increases ranging from zero, in the historic center of the city, to 0.6C in the area of most intensive urban development.

What it means
In the words of the author, "the case study of Vienna illustrates the weakness inherent in studies which use only two stations to describe urban heat islands or use linear regression models to connect population directly to heat island intensity and trend," both of which procedures are typically used in making corrections for urban heat island effects in studies of global near-surface air temperature trends. Hence, it would appear that more detailed analyses of urban development characteristics will be needed before we can be confident that the global temperature record of the past century or so is properly corrected for these phenomena. And until this is done, it would be premature to put too much faith in that record as it stands today.


Reviewed 29 November 2000