A plunge in copper to a five-year low pushed the metal to the top of a growing list of worries for stock market bulls.
Copper, widely followed for its ability to often predict a slowdown in global economic activity, joins crashing oil, record-low bond yields and a spiking U.S. dollar as top threats to a bull market that's two months away from turning 6 years old.
"Since OPEC does not control the supply of copper it is hard to blame the copper price decline on a price war," said Brian Kelly of BKCM in Greenwich, Connecticut, who is short the metal. "Therefore, the logical conclusion is that the global economy is slowing."
A technical breakdown in the price chart, building inventories and a new global growth report from the World Bank point to further losses for copper and perhaps then, global stock markets as well, on fears of what the predictive metal is signaling.