The London Metals Exchange three months copper closed around $US6091 a tonne on Friday - down from the four and a half year high on June 7 of $US7,348 a tonne – a fall of almost 20 per cent.

In New York the Comex price is down by a similar amount - from $US3.3195 a pound on June 8 to $US2.764 on Friday.

The huge Chilean copper industry is normally key and although the country’s production remains tight with concerns of industrial disputes in South America which normally keep the price high, not having any affect this time round.

And with copper an increasingly important component of electric vehicles and solar batteries you would think the copper price should be soaring on increased demand.

So what is happening?

My gut feel is nervousness over the longer-term effects of Donald Trump’s reintroduction of US tariffs on various industries and the likely ensuing trade war with China and the European Union.

Yet a review of trade papers is showing some other factors at play.

The Financial Times pointed out last week “That is going beyond just one Chilean strike being deferred or a Chinese investor club breaking up”.

“The metal is giving western investors a clear signal to sell risk assets or at least reduce their portfolio weighting,” the Financial Times said.

“Right now the copper price is saying we are not far from a more general sell-off in risk assets.”

But the trade war is the major concern and copper is a particularly sensitive indicator.

Economist Stephen Bartholemeusz in the Sydney Morning Herald said the copper price is often given the honorific 'Doctor' because of its sensitivity to the world’s economic health.

He said “the patient is coming down with something nasty” and trade tensions have reached a critical point. Unless China and the EU make significant concessions to the US we will be confronting a full-scale global trade war which will damage all economies and “potentially throw the global economy back into a recession it isn’t well-equipped to deal with.” – Derek Barry