The United Nations food price index was already higher in real terms than at the height of the global hunger crisis a decade ago, when Tunisian bread protests set off the Arab Spring.

The tight global market for grains, vegetable oil and fertilisers was probably one of the many reasons that Putin chose this moment to strike, calculating - wrongly it may prove - that the West would not dare to squeeze him too hard.

The world faces what amounts to a commodity "black swan" across the gamut of primary resources. Oil, gas, coal and the "ags" are all spiralling higher together, with metals catching up fast. It is a systemic stagflation shock, an intractable problem for central bankers. It acts like a war reparations tax on the economies of importing nations and is ultimately contractionary.