China has just announced that last year, for the first time since it began opening up its economy to the world at the end of the 1970s, exports declined on an annual basis. And that is not all; in value terms, global trade declined in 2015. The obvious question is why.

While global trade also fell in 2009, the explanation was obvious: The world was experiencing a sharp contraction in GDP at the time. Last year, however, the world economy grew by a respectable 3%. Moreover, trade barriers have not risen significantly anywhere, and transport costs are falling, owing to the sharp decline in oil prices.

Tellingly, the so-called Baltic Dry Index, which measures the cost of chartering the large ships that carry most long-distance trade, has fallen to an all-time low. This indicates that markets do not expect a recovery, meaning that the data from 2015 could herald a new age of slowing trade. The obvious conclusion is that the once-irresistible forces of globalisation are losing steam.

The situation in China is telling. In recent decades, as it became the world’s leading trading economy, China transformed the global trading system. Now the value of both imports and exports have fallen, though the former have declined more, owing to the collapse of global commodity prices.

In fact, commodity prices are the key to understanding trade trends over the last few decades. When they were high, they drove increased trade – to the point that the share of trade to GDP rose – fuelling hype about the inevitable progress of globalization. But in 2012, commodity prices began to fall, soon bringing trade down with them.

Assume that one ton of steel and ten barrels of oil are needed to produce one car. In 2002-2003, that bundle of raw materials was worth around $800, or about 5% of the value of a $16,000 car. This implies that, during the early 2000s, industrial countries had to export five cars for every one hundred bundles of these raw materials they imported.