(Arlington, VA November 4, 1998) In a special report released today, Greening Earth Society science advisor Robert C. Balling, Jr., analyzes trends in United States "degree days" between 1950 and 1995 to see if they contain evidence of "global warming." Balling, who is Director of the Arizona State University Office of Climatology, explains that trends in "heating degree days" in northern latitudes and "cooling degree days" in southern ones should serve as a surrogate in detecting changes in climate because they represent the energy required to control climate in buildings throughout the year. Balling s study reveals no statistically significant trends over the period of study (1950-1995).
According to Balling, heating degree days in the United States have decreased by 0.2%, cooling degree days have decreased by 5.7%, and the total degree days have decreased by 1.0% over the 1950 to 1995 period. He notes that although such a trend is far from being statistically significant, the largest change is in the decrease in cooling degree days which should be increasing if climate is warming, as predicted by computer-based General Circulation Models of climate.
"Despite all the publicity about increasing mean temperatures, increasing extreme high temperatures, and an increase in the frequency, duration, and magnitude of summer heat waves," Balling writes, " cooling degree days in the United States have declined slightly indicating a small reduction in the energy needed to cool buildings."
Balling s methodology involves use of Daily Historical Climatology Network temperature data, a database prepared by the National Oceanic and Atmospheric Administration that contains daily maximum and minimum temperature values for over 1000 stations in the conterminous United
States. According to. Balling, the data have undergone extensive quality control screening and represent the best daily temperature time series available for any part of the globe.
Concerning the validity of such an analysis, Balling points out that NASA climatologist James Hansen and colleagues incorporated degree days in their "common-sense climate index." Balling also notes that the study period corresponds with a time of substantial buildup of greenhouse gases in the planetary atmsophere. "Numerical climate model predictions suggest a decrease in heating days and an increase in cooling degree days for rising levels of greenhouse gases," he concludes. "Our analyses of degree day patterns from the historical climate records do not provide empirical support for the model simulations."
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