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A Century of Climate Change in the Central United States
Reference
Suckling, P.W. and Mitchell, M.D. 2000. Variation of the Koppen C/D climate boundary in the central United States during the 20th century. Physical Geography 21: 38-45.

What was done
The authors studied the spatial and temporal variation of the C/D Koppen climate boundary in the central United States over the 100-year period 1900 to 1999. In this climate classification system, the C and D climates are both considered mid-latitude rainy climates, but with mild and cold winters, respectively. The data used in the analysis were mean January temperatures obtained from the U.S. Historical Climatology Network for 67 sites located between 37 and 41.5N latitude and 90 and 100W longitude, comprising much of Missouri, eastern and central Kansas, south-central and southeastern Nebraska, southern Iowa and west-central Illinois.

What was learned
Breaking the hundred-year time period into four equal parts, it was found that the C/D climate boundary was located slightly farther south during the last two periods (1950-1974 and 1975-1999) than it was during the first two periods (1900-1924 and 1925-1949). In the words of the authors, "this implies that winters were colder or more severe during these latter periods compared to the two earlier quarter-century periods." They also note that "cooler conditions for the latter half of the 20th century are further illustrated by the network-wide mean January temperature values," which were -3.34C for 1950-1974 and -3.24C for 1975-1999, as compared to -2.67C for 1900-1924 and -2.62C for 1925-1949.

What it means
The results of this study clearly show, contrary to the predictions of some - such as Butzer (1980), for example - that a northward migration of climatic zones in central North America does not appear to be occurring. The authors say that "this suggests a lack of evidence for any systematic wintertime warming in the central United States that might be anticipated under a global-warming scenario." They also note that the same holds true for the summer-sensitive Dfa/Dfb climate boundary (where Dfa climates have distinctly warmer summers than Dfb climates), as demonstrated by Mitchell and Kienholz (1997) in a similar study based on July mean temperatures in the north-central and northeastern United States. These studies thus make an even stronger case than we make for the non-existence of global warming, as we only claim it has not warmed since 1930 (see our Editorial of 1 July 2000).

References
Butzer, K. 1980. Adaptation to global environmental change. The Professional Geographer 32: 269-278.

Mitchell, M. and Kienholz, J. 1997. A climatological analysis of the Koppen Dfa/Dfb boundary in eastern North America, 1901-1990. Ohio Journal of Science 97: 53-58.