A couple of weeks ago in Mobile, Ala., this correspondent watched a shipyard auction where spools of copper cable were fetching prices that had some participants shaking their heads. In a bidding frenzy, one buyer won every single spool, spending about $1,000,000 in total. Then he bundled them onto a ship headed for China where they'll be stripped, ground up and melted into new metal.

Right as that was happening, financial market prices for copper - along with a host of other commodities - were slumping as traders fretted that Europe's financialcrisis could swamp global demand.

So, who was right, the buyer in Mobile or the financial markets? The Baltic Dry Index suggests the former.

The index, which measures global shipping costs for bulk commodities, has risen 22% in May, putting it at its highest levels in six months. Since it's very sensitive to demand for moving goods around the world, it tends to be a good measure of whether the global economy is heating up or cooling down.

The disconnect between the Baltic Dry and commodity prices is unusual. So too is the way that commodity prices have been moving in sync with each other in recent years. A recent paper by economists Ke Tang at Renmin University in China and Wei Xiong at Princeton University documents how commodity prices have become increasingly correlated with one another and with stock prices.

The reason, the economists argue, is that commodities have become increasingly 'financialized' by the creation of exchange-traded funds that allow investors to easily trade in and out of them. So when investors get worried by things like what's going on in Europe, commodity prices can fall sharply even though actual demand for commodities may be running higher.

Justin Lahart

• correspondent [,kɔri´spɔndənt] n.记者 a.符合的 (初中英语单词)
• copper [´kɔpə] n.铜 a.铜制的 (初中英语单词)
• financial [fi´nænʃəl] a.金融的，财政的 (初中英语单词)
• shipping [´ʃipiŋ] n.船运业；船舶(总数) (初中英语单词)
• measure [´meʒə] n.量度；范围 vt.测量 (初中英语单词)
• economy [i´kɔnəmi] n.经济；机制；组织 (初中英语单词)
• unusual [ʌn´ju:ʒuəl] a.不平常的；异常的 (初中英语单词)
• creation [kri´eiʃən] n.创作；作品；创造 (初中英语单词)
• sharply [´ʃɑ:pli] ad.锋利地；剧烈地 (初中英语单词)
• actual [´æktʃuəl] a.现实的；实际的 (初中英语单词)
• running [´rʌniŋ] a.奔跑的；流动的 (初中英语单词)
• crisis [´kraisis] n.转折点；危机 (高中英语单词)
• sensitive [´sensitiv] a.敏感的；感光的 (高中英语单词)
• commodity [kə´mɔditi] n.日用品；商品 (高中英语单词)
• auction [´ɔ:kʃən] n.&vt.拍卖 (英语四级单词)
• frenzy [´frenzi] n.&vt.(使)狂乱 (英语四级单词)
• happening [´hæpəniŋ] n.事件，偶然发生的事 (英语四级单词)
• increasingly [in´kri:siŋli] ad.日益，愈加 (英语四级单词)
• baltic [´bɔ:ltik] a.波罗的海的 (英语六级单词)