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 US:HGZ5. 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.