Is China’s lumbering economy weighing on copper futures? Copper futures are plumbing the depths. The base metal is hovering around its worst levels since 2009, and that may be a telling sign about the state of the global economy, specifically China. As the world’s No. 2 economy, China is one of the biggest importers of metals, like copper HGZ5, -0.16% Financial blogger Wolf Richter says China represents 40% of global demand. Copper is a key component in manufacturing everything from electronics to cars and other industrial goods, but signs of a slowdown in China are starting to play out in some of the commodities most associated with its decades-long growth path. On Wednesday, China reported a slowdown in its breakneck gains in industrial output. Copper has sunk by about 22% so far this year, and it doesn’t look as if that slump is abating. Citing Richter, MarketWatch’s Need to Know column points out that copper’s price has hit its lowest levels since around the summer of 2009. Here’s a look at copper’s moves over the past decade, illustrated via this FactSet chart: A plan by Glencore PLC GLEN, +3.20% to cut its copper-mining activities for 18 months, announced in September, briefly halted copper’s fall, but that effect appeared to be fleeting. As a base metal, copper represents a fundamental supply/demand dynamic. Greater demand for copper pushes prices up and higher prices support the efforts of companies to mine for copper. When supplies have outstripped demand, the price has fallen. Underlying this is that strong demand usually points to an economy that is firing on all cylinders, which seems to be the opposite of what copper is telling us now. Since 1994, copper prices have been negatively correlated to the S&P 500 indexSPX, -1.40% meaning that the two have moved in the opposite direction. That changed around 2005, and copper prices moved in step with stocks, climbing as the S&P 500 rose. That trend broke down in 2012 as this chart illustrates: The S&P 500 is shown in red and the dollar is in blue, in the above chart. The divergence in the mid to late-1990s may have been tied to oversupply, as miners took advantage of then-high prices for copper to mine for more of the metal and make a profit, as the book “Commodities Rising: The Reality Behind the Hype and How to Really Profit in the Commodities Market,” suggests. More from MarketWatch