A key barometer for the global economy, copper, broke through key support today, sending out a danger signal for the metal and possibly stocks and other risk assets as well. The metal finished the day at $3.1875, its first close below key $3.20 support since October 2011. "It reminds me a lot of gold before that big breakdown," says Auerbach Grayson's Richard Ross. "This is the first significant break in two years," Ross says, and when gold broke below that level it broke hard. Ross thinks copper is setting itself up for precisely that type of move.