Letter concerning the paper ‘global cooling?’

The paper by Damon and Kunen [1] is an attempt to examine recent climatic change or variation in the Southern Hemisphere with the very limited data that are available. The criteria they used to select stations is rigorous and the authors deserve credit for detailing this procedure. Once the stations that met the criteria were identified, the monthly temperatures for each station were aggregated into means for three solar periods. This aggregation was undertaken to minimize any periodicty that might be inherent in the data because of solar activity. However, the authors do not attempt to tie the changes they see in their aggregated data back to solar activity which was their organizational basis. It is quite possible that the aggregation of these temperatures into means for three solar periods may be masking more significant trends. Many of the trends the authors did identify came from the analysis of means for latitudinal bands, cities and continents. These means of means may be valid, but there are other ways to interpret the same data. Assuming that this data set is a good representation of the behavior of recent temperature trends in the Southern Hemisphere, there appears to be little support for saying the Southern Hemisphere cities are systematically getting warmer and certainly, there is no reason to believe the warming trend is applicable only to cities above a threshold population of 750,000 persons. The authors looked at changes in the urban areas by examining means for aggregates of cities - the aggregation being based upon population. They show that for the six largest cities there has been a systematic increase in temperature over the 23rd-25th solar periods. But for the four largest cities - Rio de Janeiro, Lima, Sydney, and Santiago, all over 2 million the means show that these urban areas had an average increase in temperature of 0.025~ between the 23rd and 24th solar period but had an average decrease in temperature of 0.050~ between the 24th and 25th solar periods. Thus, over the interval considered by the authors, the four largest cities on the average were cooling or showing no temperature change. The reason why the mean for the six largest cities showed a steady increase is because the fifth and sixth largest cities- Salvador and Montevideo - reported increases in temperature between both solar periods. Not surprisingly, the evidence for urban heating varies with the statistics selected for examination. Damon and Kunen looked at the three stations with populations between 500,000 and 750,000 and noted that two of these stations showed a net decrease in temperature so they concluded "... that in this analysis the urban effect is neghgible for cities with populations below 750,000" [1, page 449]. In light of the fact that three of