While North American stocks bounced around in afternoon trading on Thursday, reflecting no particular concern about the European debt crisis and the U.S. economy, copper is sounding clear alarms among some investors. Copper prices fell as much as 7 per cent, which is the biggest one-day dip in four weeks, and brings the total decline since August to about 30 per cent.

This is a big deal because many observers believe that copper’s wide industrial uses make it a proxy for global economic conditions. Hence, its nickname, Dr. Copper. As Reuters reports:

“Copper tends to lead other markets. If copper prices are starting to begin another leg lower now – nearly 10 per cent in just two days – that’s not just a blip on the radar ... it is indicative of investors’ concern about the global economy,” said Adam Sarhan, chief executive of New York-based Sarhan Capital.

“Copper right now is signalling that the global economy might be in for a double dip.”