Why zero interest rates might lead to currency volatility

A GENERATION OF English cricket fans know the Aussies are loth to surrender a lead. For much of the past two decades, Australia has been a high interest-rate economy. But not any more. In March the Reserve Bank of Australia (RBA) cut its benchmark cash rate to 0.25%. That is the lowest interest rates have ever gone, and as low as they are likely to go. To signal its intentions that rates will stay put, the RBA has pledged to fix three-year-bond yields at 0.25%.

The Australian case is telling. Near-zero interest rates are the norm in rich countries. Very low interest rates are common elsewhere, too. Indeed, among the more prosperous sort of emerging market, only Indonesia, Mexico, Russia and the inflation-prone Turkey have short-term interest rates above 4%. Rock-bottom rates have gone global to a much greater extent than after the financial crisis of 2007-09. And a lot of central banks, like the RBA, are committing themselves to keeping rates low.

It is natural to think that if interest rates are glued to their effective lower bound, exchange rates will be similarly stuck. An axiom of foreign-exchange analysis is that shifts in policy rates, or in expectations of policy rates, drive currencies up and down. Yet a zero-rate world might plausibly imply more currency volatility. There is little scope for interest rates to...