He used 2019 data as the most recent year when trade was considered „normal” before Covid-19 disrupted global trade and conducted an analysis of trade between non-neighboring countries, as those who share a border are more likely to use land routes.
About 1,000 miles northeast of the Straits of Malacca, the South China Sea is home to no fewer than seven countries, making military conflict the most obvious risk.
„Both the Straits of Malacca and the South China Sea are chokepoints estimated to carry the most trade in terms of total value and total weight,” Bradson writes.
The South China Sea alone has trade equivalent to 5 percent of global GDP, making it the world's fourth largest economy.
How exactly trade flows in the South China Sea is a highly debatable point. The Washington-based Center for Strategic and International Studies put the value at $3.4 trillion for 2016, 36 percent lower than other estimates for the same period.
Bretson says $4.1 trillion in 2019, with $3.9 trillion passing through the Straits of Malacca. There is some overlap because goods pass through multiple sea lanes en route to their final destination.
The exact number doesn't really matter. What is important for shippers, manufacturers and governments is to understand the severity of the impact in the event of a disaster.
The ripple effect of completely closing any waterway can be felt thousands of miles away.
Bradson notes that when the Ever-Given freighter closed the Suez Canal three years ago, it added nine days to the Taiwan-Netherlands voyage, raising the cost to global trade to $10 billion a day.
The 20-mile-wide Ombai Strait, 7,000 miles away — between Indonesia's Alor island and Timor — would see a 90 percent drop in traffic if Suez were closed.
Even the Strait of Gibraltar, which separates Europe and Africa — 2,000 miles northwest of Suez — would lose 28 percent of its shipping by value.
But the biggest impact could be the closure of the Straits of Malacca or the South China Sea.
Stopping sea traffic here would mean a 14-fold increase in trade flows in the lesser-known Lombok-Magassar Strait, north of Bali. We have yet to see if this water has the capacity to safely carry that much.
More than 20 percent by value of all mechanical machinery, electrical equipment, mineral fuels such as coal, gas and oil, and rare metals or minerals pass through the Straits of Malacca.