IF TRADE routes are the global economy’s circulatory system, the port of Long Beach is one of the valves. Last year the port processed 6m containers, making it America’s second-busiest (neighbouring Los Angeles is number one). Nearly 5,000 vessels visited Long Beach in 2012. Their scale is vast. The OOCL Asia, a container ship observed recently by your correspondent, resembles a floating car park. It has a capacity of 8,000 twenty-foot-equivalent units (TEUs); vessels that can carry almost three times as much may be on the way.

Trucks line up at the port entrance, gleaming in the Californian sun: the grubby fleet of yesteryear has largely been retired by environmental rules. The containers are unloaded, stacked and eventually picked up for distribution across America—by train if the destination is over 600 miles (966km) away, otherwise by truck. After the trucks pass through a mandatory check for radioactivity, many of them will head to warehouses in the Inland Empire, the urban sprawl east of Los Angeles.

Ports like Long Beach cannot tell the whole story of world trade. Although up to 90% of trade by volume is seaborne, low-value “dry bulk”, like the scrap metal piled up at one Long Beach terminal, accounts for about half of it. Small, valuable stuff often goes by air. According to Jock O’Connell at Beacon Economics, a consultancy, the average value of a kilo of containerised cargo arriving at Los Angeles/Long Beach ports in the first 11 months of 2012 was $6.34; at LAX airport it was $102.78.

But Long Beach still offers a prism on the global economy, and on US trade in particular. For one thing, the airborne share of trade is declining as the efficiency of seaborne trade grows. Los Angeles and Long Beach are spending over $5 billion between them on infrastructure to cope with ever-larger ships. Long Beach is building Middle Harbour, a 321-acre (130-hectare) container terminal that will be able to receive vessels of up to 18,000 TEUs. This month construction began on a replacement for the Gerald Desmond bridge, which will allow larger vessels to penetrate deeper into the harbour.

The routes plied by these ships provide clues to the strength of the world’s big economies. Throughout the 1990s and 2000s Los Angeles and Long Beach ports benefited as Asian countries, particularly China, were integrated into the global trading system (see charts). Container traffic at Long Beach has more than doubled since 1995. Trade volumes slumped dramatically in 2008-09, and activity has yet to regain its pre-crisis peak. But the outlook is strong: a 2009 report predicted a doubling of container traffic at Los Angeles/Long Beach by 2030. A proposed Pacific free-trade agreement could boost maritime trade further; Europe’s doldrums have already seen ships redeployed to transpacific routes.

The cargoes that fill the ships at America’s ports reflect changes in US consumption patterns (eg, fewer oil imports as domestic production increases). They also illuminate rising wealth abroad: last year the value of agricultural products exported from west-coast ports exceeded that of recyclable materials for the first time, thanks in part to Asia’s growing taste for meat. And the proportion of containers that leave the terminals empty after having arrived full tells a story about America’s persistent trade deficit. Last year at Long Beach it was about half. This proportion may well shrink. In 2010 Barack Obama called for a doubling of American exports within five years. That goal is starting to look too ambitious, but the export sector has been outpacing the economy: in the 12 months to September 2012 American exports of goods and services were worth over $2.1 trillion, 38% more than in 2009. A big boost could come from the export, in liquefied form, of the natural gas opened up by America’s shale boom. The Department of Energy must approve all LNG exports, and licences for most countries are hard to obtain. But producers are hungry to take advantage of higher prices abroad. Asia currently accounts for almost two-thirds of global LNG imports. This leaves Pacific states like California well placed to take advantage, should politicians adopt a more relaxed attitude. Other developments may not help the west coast. The much-heralded expansion of the Panama Canal, now postponed until April 2015, will make room for vessels with a capacity of up to 13,000 TEUs (only tiddlers below 4,400 TEUs are now allowed). Over time that could mean a shift of business away from Long Beach to east-coast and Gulf of Mexico ports, though how much will partly depend on the canal’s fees and the capacity of these ports.

Anthony Otto, president of Long Beach Container Terminal, does not sound too concerned. Last year LBCT’s Hong Kong-based parent company placed a big bet on Long Beach’s future by taking out a 40-year, $4.6 billion lease at Middle Harbour. The transit times, facilities and cost structure at Long Beach, says Mr Otto, will ensure it stays the “preferred gateway” to American consumers for many shippers.

But some things the port can do little about. One is the growth of non-traditional trade routes (see article). The China-Brazil connection is increasingly vital. Pascal Lamy, head of the World Trade Organisation, has suggested that Africa could be China’s biggest trade partner within three to five years. Another challenge is “nearshoring”, the shift of manufacturing capacity closer to American consumers (see our special report). Mexico has been the big winner here: since 2010 it has outpaced China in increasing its exports to America. Most goods travel over land: fine news for truckers and trains, less so for ports.