Eduardo Porter tells readers about confusion among central bankers about how to deal with international capital flows and asset bubbles like the housing bubble in the United States. While there has been considerable confusion among central bankers, this appears to be more linked to their lack of qualifications than the intrinsic complexity of the subject matter.

For example, Porter notes how Greenspan was confused by the inflow of foreign capital that kept long-term interest rates low even as he was raising short-term interest rates.

"It was a wave of money that — to the confusion of Alan Greenspan, the Fed chairman at the time — the Fed seemed powerless to manage."

This was Greenspan's famous "conundrum." Of course it was not a conundrum to those who closely followed the economy at the time. It was easy to see that China and Japan's central banks were buying up long-term U.S. bonds, directly lowering long-term interest rates, while Greenspan was trying to affect long-term rates indirectly by raising short-term rates. (This was in effect a form of quantitative easing, but by foreign central banks.) Needless to say, directly acting in the market had more of an impact than indirectly acting.

The low interest rates that fuel asset bubbles should be good for the economy. The priority of the central bank should be to use its regulatory powers to prevent credit from flowing to markets that are experiencing dangerous bubbles.

It can also explicitly warn that it will take measures to bring down asset prices if they continue to grow further out of line with fundamentals. This would in effect be a form of forward guidance. While economists routinely deride the idea that such warnings could impact the behavior of investors, many of these same economists believe that central bank statements about future interest rates can have a large effect.

It is difficult to see the logic whereby central bank statements in one area will affect investors' behavior while it will have no effect in another area. It is also very difficult to see the downside from issuing such warnings. Comparing the Congressional Budget Office's projections of GDP from 2008 with actual GDP and its current projections, the collapse of the housing bubble will have cost the country more than $24 trillion in lost output through 2024 ($80,000 per person). Given the enormous potential gains from measures to stem the growth of such dangerous bubbles, it is hard to see any remotely offsetting downside risk.