What was done
Working on the Korean peninsula with temperature data from 4 cities covering the period 1909-2008, 12 cities covering the period 1954-2008, and 20 cities covering the period 1969-2008, the authors first derived values of the total warming of the cities over the different periods of record. Then, values of the urban warming effect were derived, as they describe it, "by using the warming mode of Empirical Orthogonal Function (EOF) analysis of the 55 years of temperature data from 1954 to 2008," after which the estimated amounts of urban warming were verified by means of a multiple linear regression equation with two independent variables: the rate of population growth and the total population. And by subtracting the temperature increase due to urbanization from the total temperature increase of each city, they obtained what they call "greenhouse warming," although it should more appropriately be identified as background warming, natural warming or non-urban-induced warming, for things other than greenhouse gases may well be playing a major role in the non-urban-induced portion of the total observed warming.

What was learned
Kim and Kim report that the mean total warming of the 12-city conglomerate over the period 1954-2008 was 1.37°C, of which 0.77°C was due to the concomitant growth of their urban heat islands, while the remaining 0.60°C was due to other factors. In addition, they found that "urban warming depends more on the population percent growth rate than the average population." In the case of Pohang and Incheon, for example, which "have rapidly increasing populations due to rapid industrialization," they say "the degree of urbanization was great." In the case of Busan, on the other hand, which has a large and steady population, they discovered that "the degree of urbanization was weak," illustrating the fact that "the rising trend of temperature appeared stronger in newly industrialized cities more than in large cities."

What it means
In introducing their study, the two Korean researchers stated that the IPCC (2007) had reported that "global mean temperature increased about 0.76°C from 1906 to 2005," that "the average temperature increase in East Asia is about 1°C greater than the global average," and that "the temperature increase in South Korea is estimated to be about 1.5°C greater than East Asia." And now their results indicate that "because South Korea industrialized rapidly," there is a validated reason for those observations being what they are.

Reference
IPCC. 2007. Climate Change 2007: The Physical Science Basis. Solomon, S., Qin, D., Manniing, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. and Miller, H.L. (Eds.), Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.