The NY Fed. Back in 2012, NY Fed staffers wrote "If Interest Rates Go Negative . . . Or, Be Careful What You Wish For" it warned "if rates go negative, the U.S. Treasury Department's Bureau of Engraving and Printing will likely be called upon to print a lot more currency as individuals and small businesses substitute cash for at least some of their bank balances."

Then, last October, Bank of America looked at the savings rates across European nations which had implemented NIRP and found something disturbing: instead of achieving what what central banks had expected, it was leading to precisely the opposite outcome: "household savings rates have also risen. For Switzerland and Sweden this appears to have happened at the tail end of 2013 (before the oil price decline). As the BIS have highlighted, ultra-low rates may perversely be driving a greater propensity for consumers to save as retirement income becomes more uncertain."