Copper touched $3.1215 a pound ($6,882 per tonne) in morning trade, the highest since mid-September 2014 before paring some of the gains. Copper is now up close to 50% compared to this time last year.

According to Reuters weekly copper stocks in warehouses registered by the Shanghai Futures Exchange declined by more than 8% over the past week to 187,444 tonnes while in LME warehouse so-called on-warrant inventories – those not earmarked for removal – have halved to 112,950 tonnes over the past six weeks.

No 1 producer joins copper rally skeptics as price hits new 3-year highIn contrast Comex stocks have climbed to levels last seen in 2004 and at 181,072 this week have tripled since November 2016, at least in part due to unprecedented speculative interest from hedge funds.

On Tuesday, the chairman of the world's number one producer, Chile's Codelco, joined the chorus expressing doubts about the sustainability of the recent rally:

"I'm a little skeptical…in the short-term," Oscar Landerretche said a mining conference in Chilean capital Santiago. "It's true that all of the fundamentals are good in the medium- and long-term…but I would be very cautious."
Codelco produced over 1.8m tonnes of the red metal in 2016, a 3% drop over the previous year but the state-owned firm managed to stay ahead US-based Freeport which expanded output by 12% last year to a shade under 1.7m tonnes. Codelco is likely to retain the copper crown after Freeport agreed to sell a majority stake in its Grasberg mine to the Indonesian government.

Analysts polled before copper's latest run up gave forecasts well below the ruling price. Investment banks and other institutions polled by research firm FocusEconomics forecast that prices will average $5,722 per tonne in Q4 2017 and $5,832 per tonne in Q4 2018. The lowest forecast for Q4 2017 was $4,899 per tonne, while the maximum forecast was $6,200 per tonne.

Whether copper's 13% rise in little more than a month will convince the smart money to lift their low-ball projections remains to be seen.