Teleconnections and the siege of time

The recent surge of interest in climate has resurrected correlation coefficients as tools for identifying ‘significant’ atmospheric teleconnections. Unfortunately, large coefficients may diminish and even change sign with time, suggesting absence of real physical relationships. Some statistical evidence supports the view that higher than normal sea surface temperatures in the central and eastern Pacific ‘cause’ less than normal rainfall in the Indian summer monsoon. However, a study of individual Augusts uncovers major exceptions and at the same time fails to confirm that Indian summer rainfall influences central and eastern Pacific rainfall or that the Southern Oscillation Index can be consistently related to conditions in either region. Around 1963-1964 the apparent relationship between the Southern Oscillation Index and Indian rainfall reversed. At about the same time other global climatic relationships changed, raising the possibility of identifying and describing a major global climatic singularity separating two distinct statistical populations.

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