Global economy got a serious boost from the cheap long-term borrowing available, mainly fuelled by low rates on US 10-year Treasuries.

In 2004 a lot of growth was once again driven by consumer spending in the US that helped to digest the output of many of the world’s exporting countries lacking an equally vigorous domestic demand. Saving in the US has dropped to 0.2% of after-tax income.

Low rates helped to finance durable goods such as automobiles, giving rise to the housing boom as house prices surged on low mortgage rates.

Many analysts are intrigued by the fact that interest rates remain low in spite of many factors seemingly putting upward pressure on bond yields.

"What turns this story into a mystery is economic growth turned out in line with expectations and inflation substantially higher," said Mark Cliffe, chief economist at ING Financial. "The plot thickens if we consider the U.S. dollar was weaker and oil prices much higher than anticipated."

The rates did not move higher even on the rate hike to 2.25 that came in the Fed December meeting.

The reasons that are given to offer solution to the mystery include lower inflation expectations, lower job creation against the background of strong productivity growth. The persistence of geopolitical risks drives the demand for assets safer than stocks. But perhaps the most important reason is the demand for Treasuries coming from Asian central banks, mainly Japan and China, in an effort to subsidize the country that purchases a lot of the goods these nations produce. A change in the policy of these banks envisaging the reduction of weight of dollar-denominated assets could trigger a long-term rate increase in the US.