The world economy faces an acute policy dilemma that, if mishandled, could bring on the mother of all monetary crises. Many dollar holders, including central banks and sovereign wealth funds as well as private investors, clearly want to diversify into other currencies. Since foreign dollar holdings total at least $20,000bn, even a modest realisation of these desires could produce a free fall of the US currency and huge disruptions to markets and the world economy. Fears of such an outcome have risen sharply in both official circles and the markets.

However, none of the countries into whose currencies the diversification would take place want to receive these inflows. The eurozone, the UK, Canada and Australia among others believe that their exchange rates are already substantially overvalued. But China and most of the other Asian countries continue to intervene heavily to keep their currencies from rising significantly. Hence, further large shifts out of the dollar could indeed push the floating currencies far above their equilibrium levels, generating new imbalances and a possibly severe slowdown in global growth.