On the insignificance of Herschel's sunspot correlation

Geophysical Research Letters



We examine William Herschel's hypothesis that solar-cycle variation of the Sun's irradiance has a modulating effect on the Earth's climate and that this is, specifically, manifested as an anticorrelation between sunspot number and the market price of wheat. Since Herschel first proposed his hypothesis in 1801, it has been regarded with both interest and skepticism. Recently, reports have been published that either support Herschel's hypothesis or rely on its validity. As a test of Herschel's hypothesis, we seek to reject a null hypothesis of a statistically random correlation between historical sunspot numbers, wheat prices in London and the United States, and wheat farm yields in the United States. We employ binary-correlation, Pearson-correlation, and frequency-domain methods. We test our methods using a historical geomagnetic activity index, well known to be causally correlated with sunspot number. As expected, the measured correlation between sunspot number and geomagnetic activity would be an unlikely realization of random data; the correlation is “statistically significant.” On the other hand, measured correlations between sunspot number and wheat price and wheat yield data would be very likely realizations of random data; these correlations are “insignificant.” Therefore, Herschel's hypothesis must be regarded with skepticism. We compare and contrast our results with those of other researchers. We discuss procedures for evaluating hypotheses that are formulated from historical data.
Publication type Article
Publication Subtype Journal Article
Title On the insignificance of Herschel's sunspot correlation
Series title Geophysical Research Letters
DOI 10.1002/grl.50846
Volume 40
Issue 16
Year Published 2013
Language English
Publisher Wiley
Contributing office(s) Geologic Hazards Science Center, Geomagnetism Program
Description 6 p.
First page 4171
Last page 4176
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