From the Aussie to soybeans and cars: what's at risk in a trade war?

The Aussie dollar takes a thumping, soybean prices swing and German carmaker shares are stuck in reverse.

Financial markets have been roiled by fears of an all-out trade war between the United States and China, prompting investors to dump assets at risk from rising tariffs and seek safety in havens such as Japan's yen and US Treasury bonds.

US President Donald Trump's promised this week to slap tariffs on $200 billion of Chinese goods, drawing swift threats of retaliation from China.

Countries with open economies reliant on global trade are most at risk when disputes over international commerce hit.

The Australian dollar ticks those boxes. Australia counts China as its biggest trading partner and its currency is heavily correlated to global growth. Many investors see the currency, known as the Aussie, as a better global trade bellwether than the Canadian dollar, which has been buffeted by negotiations over Nafta, the North American trade pact.

This week, the Aussie fell to its lowest level in 13 months, and the positioning of options signal more weakness ahead.

Another candidate is Sweden's crown, given the Nordic nation's open economy and big exporting industries. The currency has weakened about 2.5 percent in the last three days to a six-week low against the euro.

“Currencies which are heavily exposed to global growth are going to feel the pressure from any escalation in the trade dispute,” said James Binny, global head of currency at State Street Global Advisors based in London.

Asian currencies such as the Korean won as well as the Singapore and Hong Kong dollars have also weakened this week for similar reasons.

Bank of America Merrill Lynch's European fund manager survey in June found a record drop in allocations to auto stocks, indicating that investors are jittery about the sector due to Trump's threat of imposing US tariffs on German carmakers.

European automakers send around $50 billion worth of cars to the United States each year. BMW is the most exposed with up to one fifth of its global sales heading to the US market.

Retaliatory Chinese tariffs on US cars would also hurt European firms as many export to China from their US plants.

As a result, shares in Volkswagen, BMW and Daimler have fallen sharply, taking Europe's autos index to a seven-month low.

The aircraft industry, including Boeing and Airbus, is another barometer as it relies heavily on an open global supply chain.

Boeing is the single largest US exporter to China, and its shares, along with those of its European counterpart, have fluctuated as trade tensions have risen.

Steel and aluminium are regular targets in international trade disputes. US tariffs on imported steel have hit shares in European steelmaking exporters such as Thyssenkrupp, Salzgitter and Voestalpine.

Europe-based manufacturers that import steel for US factories may also become entangled in the conflict.

There could be some winners, if European manufacturers such as ABB and Siemens win market share in China at the expense of US rivals such as Honeywell.

But higher trade barriers are likely to hurt most economies, leaving even the winners with a smaller market to work with.

China buys about a third of its soybeans from the United States so Beijing's move to slap 25 percent duties on US soybean imports has made the commodity a key battlefield.

It will raise the cost of soymeal, which is used in China to feed pigs and poultry. China's most active soymeal futures rose 4.2 percent on Tuesday.

Soybean prices tend to be affected more by weather than economic factors, but tit-for-tat tariffs might shift trade flows. US soy futures have tumbled to multi-year lows as US suppliers may now lose a chunk of China's market to Latin American rivals.

Finally, prices for copper, a metal widely used in the construction and power industries, have fallen to their lowest since May 31. Copper prices can be expected to tumble further if world growth slides.