Noah Smith is a Bloomberg Opinion columnist. He was an assistant professor of finance at Stony Brook University, and he blogs at Noahpinion. Read more opinion SHARE THIS ARTICLE Share Tweet Post Email

Photographer: Samuel Corum/Anadolu Agency/Getty Images Photographer: Samuel Corum/Anadolu Agency/Getty Images

Why are interest rates so low? For macroeconomists, this is one of the Big Questions in the world today.

Government bond rates are at or near record lows all around the world. So are corporate bond rates, including junk bonds. Even the cost of equity capital is at or near an all-time low for most businesses. Whether you’re a government, a big corporation or a tiny startup, it has never been cheaper to obtain capital.

Interest rates of all kinds have been in decline since the early 1980s. For a while, that looked like a simple regression to the mean. The early '80s saw central banks tighten a lot, driving up rates in an effort to rein in inflation. But the decline that we’ve seen during the past 15 years or so -- and especially since the financial crisis -- goes way beyond a simple normalization. Something unusual is happening.

That’s worrying for macroeconomists, because it means that old theories may be wrong. It’s also worrying for central bankers because it constrains their actions (nominal interest rates can’t be pushed below zero) even as it increases the uncertainty under which they are forced to make their decisions.

So why are rates so bizarrely low? Interest rates are set in markets, where borrowers meet lenders (broadly defined). Any explanation for falling rates must involve an increased desire to lend, a decreased desire to borrow, or both.

One common theory is that central banks are responsible. This makes sense to most people, since we all hear that the Federal Reserve, or the Bank of Japan, has a policy of holding interest rates near zero. But just because central banks are setting their rate targets at zero doesn’t mean that they have to work very hard to achieve that target. If private markets are trending toward low interest rates on their own, it means that central banks have basically been a sideshow.



QuickTake Less Than Zero

In other words, the Fed may be a little like the annoying younger brother who tells you to “keep breathing,” and then gloats about how he made you obey him.

There are reasons to think that central banks are not the big driver of low rates. First of all, it isn’t just nominal rates that are historically low, but real inflation-adjusted rates as well. Most economists believe that real interest rates can’t be affected by monetary policy for very long. Second, most economists think that if central banks are holding rates below what private markets want, we should be seeing high inflation. We’re not. And finally, the end of the Fed’s bond-buying program of quantitative easing seemed to have only a small effect.

So are low rates being driven by a savings glut? That was the famous hypothesis of former Fed Chairman Ben Bernanke in 2005. The idea was that developing countries -- for example, China -- were saving more than they were investing, and that the excess capital was flowing into the U.S. and lowering borrowing costs. Since the financial crisis, savings rates have risen in the U.S. as well -- households are squirreling away more of their paychecks, and corporations are famously hoarding cash. The savings glut might have gone global.

Another reason for low rates -- an underrated reason, I suspect -- could come from the demand side of the equation. The desire to borrow money clearly seems low across the world.

Households in the U.S. and other countries that suffered a big housing bust have large overhangs of debt, and the crash showed them that debt was more dangerous than they had realized. Companies in Europe are clearly reluctant to borrow to invest, given the running political uncertainty surrounding the euro and the sovereign debts of countries such as Greece. That probably applies to Japan as well. In addition, these rich countries have steeply declining populations, and shrinking domestic markets discourage companies from expanding.

As for U.S. companies, they may be holding back investment because of fears of weakness in export markets. China is slowing, and with it many other developing countries. Another factor may be the recent wave of technological disruptions that make it harder for companies to plan ahead. Big investments require big bets, and in an era of massive disruption, no one knows which bets to place. And even as disruption is increasing, overall productivity is slowing.

So what will stem the tide of low interest rates? I wouldn't count on central banks to do the job. As long as private markets keep pushing rates down, central bankers are not going to risk causing recessions by attempting to raise them. Nor are companies going to suddenly become brave and bold around the world.

There are some factors that may stop the downward slide. American households will eventually work off their debt overhang -- already, the housing market is recovering. At the same time, China is also rebalancing toward a more consumption-based economy. That should do a bit to drain the savings glut, at least when China’s current sharp slowdown has run its course.

But long-term trends -- declining global population growth and continued technological disruption -- point to a very long period of low interest rates.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

To contact the author of this story:

Noah Smith at nsmith150@bloomberg.net

To contact the editor responsible for this story:

James Greiff at jgreiff@bloomberg.net