Globally, interest rates have been trending down since the early 1980s. At first this could have been thought of as a process of normalisation, as the inflationary excesses of the 1970s were progressively squeezed out of the system. Latterly, however, and especially since the global financial crisis, the fall in borrowing costs represents something altogether more unusual and disturbing.

Standard economic theory posits that central bank policy exerts a profound influence on the interest rate term structure. In recent years, the number of central banks targeting a zero, or near zero, policy interest rate has progressively increased.