Courtesy of: Stockcharts.com Going back to commodities markets, copper has taken a beating lately. The pair above is of DJ-UBS Copper Total Return Sub-Index ETN ( JJC) over an equal-weight DB Commodity Index Tracking Fund. This pair correlates with industrial output, and has trended downward as global economic data have deteriorated. China GDP was weak recently, and the U.S. data picture has shown a gradual decline toward the end of the first quarter. Until the global economic picture looks considerably stronger over a consistent period of time, industrial metals will stay suppressed. Each global market looks to be trading in tandem, it is only a matter of time before all risk assets see a considerable pullback. At the time of publication the author had no position in any of the stocks mentioned.Follow @AndrewSachaisThis article was written by an independent contributor, separate from TheStreet's regular news coverage.