FIGURE 4

Time series of the variations of the annual mean maximum, minimum, and diurnal temperature range for the contiguous United States and the former Soviet Union. Smooth curve was obtained with a nine-point binomial filter. Trends since 1951 are depicted by the dashed line.

mean temperature reflects little overall change. In the first half of the nineteenth century the DTR averages about 0.5°C lower than in the latter part of the century. The DTR at Sodankylä, Finland, also displays a gradual decrease since 1950, but contrary to the Klementinum Observatory's pattern, the decrease is evident back to the turn of the century. The mean temperature at Sodankylä reflects little or no change. The high-frequency variability of the DTR at both stations is less than that of their respective mean temperatures, but the converse is true for low-frequency variations.

If the data from the Klementinum Observatory truly reflect the regional change of the DTR in central Europe, then the recent decrease of the DTR in this area is less persistent and less substantial than the increase prior to 1950. In light of the variations at the Klementinum Observatory, what makes the results from Figure 2 so remarkable



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