Historical temperature trends in the United States and the effect of urban population growth

The linear change in temperature between 1920 and 1984 is calculated for 961 stations in the conterminous United States. Annual, winter, and summer maps of these temperature changes reveal pronounced geographical patterns, with widespread cooling in the major south-central portion of the United States and general warming in the northeast and west. Stepwise multiple regression analysis identifies a statistically significant impact of population change on these temperature trends, even though the stations utilized in this study had a median population of only 5832 in 1980. Both the observed mean annual cooling of the country and the warming bias provided by these small urban centers suggest that we may not yet have a proper perspective on global climatic change. -Authors