The decomposition of real commodity prices using the BP filtering technique provides evidence of four super-cycles over 1865 to 2009 ranging between 30 to 40 years and with amplitudes of 20 to 40 percent higher or lower than the long-run trend. Non-oil price super-cycles follow those of world GDP, indicating that they are essentially demand determined. In contrast, causality runs in the opposite direction for oil prices. In turn, the mean of each super-cycle of non-oil commodities is generally lower than that of the previous cycle suggesting a step-wise deterioration in support of the Prebisch-Singer hypothesis. Tropical agriculture experienced the strongest and steepest long-term downward trend through the twentieth century, followed by non-tropical agriculture and metals. Again, in contrast to these trends, real oil prices have experienced a long-term upward trend, which was only interrupted temporarily during some four decades of the twentieth century.

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May 23, 2012.