Could commodity prices be in for a downdraft?

Several months ago Gluskin Sheff chief economist David Rosenberg pointed out that the Shanghai stock market appears to lead commodity prices by about four months.

Looking at the chart below, the Shanghai Composite broke down in mid-April. Fast forward four months to today and factor in yesterday's market action, not only in stocks but in commodity prices. Also consider that wheat prices, which had gone parabolic, had been pulling back for about a week, you have the makings of a serious downdraft in commodity prices.

I don't know if the four month Shanghai-CRB relationship is spurious or not, but this is a fascinating theory that can be tested in real-time.