Another week brings another round of tariff surprises from U.S. President Donald Trump. This time, it's a 25% duty on all U.S. imports of steel and aluminum on top of any existing tariffs.

Investors are selling off shares in major steelmakers, but so far this has been orderly and price moves have been fairly contained. Tariffs have become part and parcel of the "Trump 2.0" operating manual and although they carry the risk of igniting volatility, the market has become a little less hypersensitive to each individual headline.

There are clear signs, however, in the commodities world, where physical raw materials actually change hands, that traders are preparing for trouble.

The London

gold market

has seen traders scramble to move ingots to New York, which has pushed up short-term borrowing rates, out of fear that Trump could train his sights on precious metals as targets for tariffs - however distant a possibility that is.

A similar dynamic has emerged in the copper market in recent weeks.

Copper has traditionally been viewed as a good barometer for the health of the underlying global economy, given its ubiquity and hence the "Dr Copper" nickname.

When the price drops, it is often a sign of trouble that demand is weakening from anywhere from the construction to the electronics industry. Although its track record for predicting recession is not perfect, contractions in copper demand have often preceded slowdowns in global growth.

The copper price has rallied to its highest in several months, but analysts say that, right now, this has less to do with optimism over global growth and more with where traders are moving metal to stave off potential tariff risks.

In particular, metal is leaving London Metal Exchange warehouses and entering COMEX vaults. Since Trump took office on January 20, stocks of copper in LME warehouses have dropped by 3,600 tonnes, while those in COMEX warehouses have risen by almost exactly that amount.

In the meantime, the gap, or spread, between LME and COMEX futures prices has widened to $740 a tonne, its highest in around 35 years, as traders play the arbitrage - selling London futures in favor of buying U.S. ones. When Trump took office, this spread was below $240 a tonne.

In a note today, Citi strategists take a look at different ways to trade global tariff risks and the COMEX/LME arbitrage is one of them. Funds have also increased their holdings of COMEX copper futures and options in the latest week.

There are other bullish drivers for copper. Crucially, buyers in China, the world's largest consumer, are returning from the Lunar New Year holidays, which is fueling the rise in prices.

For all the correlation between metal demand and the health of the economy, "Dr Copper" may not be able to diagnose how severe the hit might eventually be.

Key developments that should provide more direction to U.S. markets later on Monday:

* Three- and six-month Treasury bill auctions

* Quarterly results from McDonald's, Loews and Vertex Pharmaceuticals

* AI Action Summit opens in Paris, France