The world passed a historic milestone in the past week when according to Fitch negative-yielding government debt rose above $10 trillion for the first time, which as the FT adds envelops an increasingly large part of the financial markets "after being fuelled by central bank stimulus and a voracious investor appetite for sovereign paper." It also means that almost a third of all global government debt now has a negative yield. The amount of sovereign debt trading with a sub-zero yield climbed 5% in May from a month earlier to $10.4 trillion, pushed higher – or lower in yield as the case may be – by rising bond prices in Italy, Japan, Germany and France.

Japan and Italy fuelled the increase in negative-yielding debt in May, with three-year bonds issued by the latter sliding below the zero mark.

The ascent of the negative yield, which first affected only the shortest maturing notes from highly rated sovereigns, has encompassed seven-year German Bunds and 10-year Japanese government bonds as both the European Central Bank and Bank of Japan have cut benchmark interest rates and launched bond-buying programmes.