A new paper for the US Monetary Policy Forum and published by the Fed warns that the institution's capital base could be wiped out "several times" once borrowing costs start to rise in earnest.
A mere whiff of inflation or more likely stagflation would cause a bond market rout, leaving the Fed nursing escalating losses on its $2.9 trillion holdings. This portfolio is rising by $85bn each month under QE3. The longer it goes on, the greater the risk. Exit will become much harder by 2014.
Such losses would lead to a political storm on Capitol Hill and risk a crisis of confidence. The paper -- "Crunch Time: Fiscal Crises and the Role of Monetary Policy" -- is co-written by former Fed governor Frederic Mishkin, Ben Bernanke's former right-hand man.
It argues the Fed is acutely vulnerable because it has stretched the average maturity of its bond holdings to 11 years, and the longer the date, the bigger the losses when yields rise. The Bank of Japan has kept below three years.
Trouble could start by mid-decade and then compound at an alarming pace, with yields spiking up to double-digit rates by the late 2020s. By then Fed will be forced to finance spending to avert the greater evil of default."Sovereign risk remains alive and well in the U.S, and could intensify. Feedback effects of higher rates can lead to a more dramatic deterioration in long-run debt sustainability in the US than is captured in official estimates," it said.