How long can low interest rates last?

Interest rates have been historically low for decades - long before the financial crisis. What are the causes? And what are the consequences? In this Vox Talk Charlie Bean discusses the findings of the 17th Geneva Report. He argues that the main cause of low interest rates globally is higher savings by the middle aged and that this cause will subside as the middle aged start to retire. But that will take decades and in the meantime there are challenges and risks for monetary policy.