One shipping-cost number quietly tracks how fast the world economy is moving

The Baltic Dry Index tracks the daily cost of chartering ships to haul bulk cargo like iron ore, coal and grain across specific ocean routes. Because it responds directly to demand for raw materials with almost no lag, economists watch it as an early signal of industrial activity, often moving before GDP figures catch up. It can also swing wildly: it fell over 90% between mid-2008 and the end of that year as global trade froze during the financial crisis.

— Baltic Exchange, Baltic Dry Index — Index established 1985