What: Shares of Century Aluminum Co (NASDAQ:CENX) plunged more than 20% today after the company reported worse-than-expected second-quarter earnings.

So what: Revenue rose 14% to $523.5 million, but costs rose dramatically and the company swung from a $20.3 million profit to a loss of $33.9 million. That equated to a loss of $0.39 per share, but adjusted for one-time items, earnings were $0.25 per share, still $0.09 short of estimates.  

Now what: Costs related to closing the Ravenswood smelter and market inventory to market hurt results, but it's commodity prices that investors need to be worried about. Exports from China are once again being blamed for increasing supply more than the market can handle, causing prices to plunge. Given this uncertainty and the weak quarterly results, I don't see a reason to buy now, and in the long term this industry is in a tough environment with so much global competition.