Copper Builds in U.S. Warehouses Ahead of Trade Cutoff

Key Moments:

Arbitrage Widens as Policy Decision Approaches

Half a million tonnes of refined copper is now sitting in U.S. warehouses, leaving the traders who accumulated it questioning whether they have constructed an effective hedge or walked into a trap.

Price benchmarks on the London Metal Exchange (LME) and the Chicago Mercantile Exchange (CME) have begun to diverge again, reviving the kind of dislocation last seen in 2025. The spread is widening as the market positions ahead of an expected U.S. Department of Commerce update on refined copper imports due later this month.

This phase, however, differs from the previous year’s episode in both structure and intensity. The trading window is narrower, positions are more compressed, and the build-up is colliding with physical storage limitations that were not present when the initial wave of metal started flowing into the U.S. in early 2025.

New Orleans Storage Bottlenecks and Warranting Risks

New Orleans currently hosts roughly two-thirds of all CME copper inventories and is described as being effectively full. Securing additional space is challenging: CME warehousing rules require both truck and rail access, and identifying industrial locations near an operational rail link in southern Louisiana is proving difficult.

Some copper is reportedly being left at the docks rather than placed inside warranted exchange facilities. That line is crucial. Copper left exposed for long enough can lose the clips and bindings required for LME warrant eligibility. If the trade reverses and this metal must be returned to the broader global market, part of it may no longer meet warranting standards.

The time horizon is also much shorter than in the previous cycle. The 2025 arbitrage window remained open for several months before U.S. authorities intervened in July. By contrast, the current opportunity has been available only for a few weeks, with a June 30 U.S. Commerce Department ruling – which will determine whether a phased tariff on refined copper proceeds – drawing closer.

The current LME-CME spread also remains well below last year’s extreme, when CME copper traded at nearly $3,000 per tonne above LME prices. The risk-reward profile today is therefore markedly different from the more extended build of the past year.

From Trade Play to De Facto Strategic Stockpile

Behind the visible arbitrage, an even more significant shift has been taking place. Since the initial tariff threat surfaced in early 2025, around 541,000 short tons (roughly 491,000 tonnes) of refined copper have been moved into CME-registered warehouses. That represents a more than fivefold increase, turning the U.S. from a relatively minor stockholding center into the primary locus for exchange copper inventories.

This accumulation has effectively created what some participants characterize as a de facto strategic stockpile, but one assembled through private-sector trading activity rather than state purchases. The government has not spent anything; it simply flagged a potential tariff, allowed traders to perform the calculations, and observed as the metal flowed in.

The commercial logic is straightforward: if Washington implements tariffs on refined copper imports, material already positioned inside the U.S. could command a substantial premium.

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Tariff Pathways: Three Market Scenarios

The pivotal question now is how policy evolves from here.

If refined copper tariffs move ahead as outlined – starting at a proposed 15% from 2027 and rising to 30% from 2028 – the owners of U.S.-based inventories would see their gains crystallize immediately. At that point, however, new imports would likely cease, as there would be little rationale for shipping fresh metal into a tariff barrier while roughly half a million tonnes already sit within it. The United States would instead draw down that stored copper over a period of a year or two, supporting global prices while keeping the trapped material largely off the broader market.

If tariffs are scrapped, the focus would shift to unwinding positions. Re-export economics only work when LME prices hold a durable premium over CME levels large enough to cover freight, interest, and handling. When the exemption of July 2025 was announced, the arbitrage flipped rapidly, with LME briefly trading at a premium in early 2026. A definitive “no tariff” decision would likely catalyze a similar, but faster, adjustment.

The most awkward outcome for market participants would be ongoing uncertainty. Another postponement, another round of “further study required,” would prolong the status quo – another year of storage fees on a wager that has yet to deliver.

The recent June 1 proclamation adjusting derivative copper tariffs, effective June 8, did not provide clarity on the refined copper question.

Global Market Tightness Behind the U.S. Stock Overhang

While U.S. inventories swell, conditions elsewhere appear tighter than aggregate global stock numbers imply. LME and Shanghai Futures Exchange warehouse levels are both significantly below their mid-2025 peaks, although the pattern of drawdown has been uneven and volatile across venues.

In Asia, fabricators are retreating from spot purchases, not because they are oversupplied, but because LME prices are considered too elevated to justify buying in a period of softer demand. Physical premiums in Shanghai have also weakened.

The export arbitrage from China to Southeast Asia briefly opened this week before compressing again. Overall, these signals are not consistent with an oversupplied market; instead, they suggest that a substantial volume of copper is simply in the wrong location.

Supply Strains From Sulfuric Acid Constraints

Additional pressure is emerging on the production side. Sulfuric acid shortages, driven by a logistics disruption in the Middle East and China’s decision to suspend acid exports through December, are constraining SX-EW output in Chile and central Africa.

Roughly 20% of global copper supply originates from SX-EW operations, which are highly dependent on sulfuric acid. Unlike disruptions such as mine strikes or pit wall failures, acid shortages reduce output within a quarter rather than over a full year, and the impact is already being felt.

Demand Holds Up as Policy Ambiguity Persists

Despite these supply-side challenges, demand indicators remain resilient. Manufacturing purchasing managers’ indexes across Asia have moved into expansion and have stayed there. Investment in power grid infrastructure is accelerating, while AI data centers show limited sensitivity to copper prices, as copper represents only a minor component of their overall capital spending.

The June 30 tariff announcement may not deliver a definitive outcome – and that may suit policymakers. Prolonged uncertainty keeps metal flows heading into the U.S., expands the privately financed stockpile, and leaves storage costs in the hands of traders rather than the government.

In Hotter Commodities, special correspondent Andrea Hotter covers some of the biggest stories impacting the natural resources sector. Read more coverage on our dedicated Hotter Commodities page here.