Recent research by Ricardo Caballero, Pierre-Olivier Gourinchas and Emmanuel Fahri suggests that the ZLB also prevents global interest rates from falling low enough for global asset markets to clear (i.e. global demand for financial assets exceeds their supply).2 In such an environment, if countries would run continuous current account surpluses, the world interest rate would fall until it hits the zero bound.
My colleague, Tiff Macklem, spoke on this topic at some length a couple of weeks ago, and you can find his remarks on our website. Determining how much of each of these forces is behind the movement in the currency is an important, but very difficult, judgment that the Bank must make.