COLUMN-An aluminium mirror on Trump's tariff tornado: Andy Home

(Repeats with no changes. The opinions expressed here are those of the author, a columnist for Reuters)

* Aluminium Premium Timeline: https://tmsnrt.rs/2GWOjHR

* U.S. aluminium imports 2017: https://tmsnrt.rs/2uQFfQ0

* U.S. product imports 2017: https://tmsnrt.rs/2GBYORD

By Andy Home

LONDON, April 6 (Reuters) - The rhetoric of trade war is escalating with each passing day.

U.S. President Donald Trump threatens another $100 billion of tariffs on Chinese goods. China warns that it will fight back "at any cost".

This storm started with steel and aluminium, with tariffs coming into effect on March 23, but has grown in intensity to encompass a lengthening list of goods and products.

Rising trade tensions have weighed on industrial metal prices, unsurprisingly given their exposure to global growth prospects, but have caused the U.S. aluminium premium market to whipsaw higher.

Which is ironic since prior to this week the premium was falling as the aluminium market realised that in its case the U.S. administration's bark has proved considerably worse than its bite.

Graphic on the CME aluminium premium contract and reactions to key tariff announcements:

https://tmsnrt.rs/2GWOjHR

A MIRROR ON TARIFF POLITICS

The CME's Midwest aluminium premium contract has provided an accurate market mirror on President Trump's seemingly chaotic approach to tariffs.

Based on the supply and logistics drivers of the North American aluminium market, it is a much more sensitive gauge of U.S. tariff impacts than the London Metal Exchange price.

It is also an increasingly popular one with contract volumes up 32 percent in the first quarter and open interest at a year's high.

The premium exploded upwards on Feb. 13, the day of the release of the Section 232 investigation into U.S. imports on national security grounds.

The report's recommendations for blanket tariffs and/or quotas propelled the CME's Dec 2018 contract from 13.0 to 16.5 cents/lb, a 27 percent jump equivalent to a $77 per tonne rise in the cost of delivered aluminium in the U.S. Midwest.

After a brief pull back it surged again to 17.0 cents/lb after Trump announced on March 1 his intention to impose duties of 25 percent on steel and 10 percent on aluminium.

Crucially, there was no talk of countries being exempted, not even Canada, the largest supplier of aluminium to the U.S. market place and one that is "integrated" with the U.S. industrial base, to quote the Section 232 report.

There was panic in Canada with officials simultaneously promising it would never happen and mulling possible retaliatory measures.