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You may not have heard of the Baltic Dry Index, but you may soon be hearing a lot about it. The Index, maintained by the Baltic Exchange in London, measures the cost of shipping commodities like coal, iron ore, and wheat, and it's at its highest point ever—7,007 as of last Friday. It now costs about $58,500 a day on average to hire a medium-sized ship, over twice what it cost just last year and nearly six times the price in 2005.

As usual with these types of things, one of the main factors is China, which is importing ever-greater amounts of coal and iron ore. Given what we know about China's growth projections, it's probably a safe bet that this is a trend that will continue into the near future. But eventually, new ships will flood the market, pushing prices back down.