The ups and downs of the U.S. stock market are largely driven by the degree to which the Federal Reserve makes easy money available. After (ridiculously) insisting for most of 2021 that inflation was merely “transitory”, chairman Powell has finally put on his big boy pants and started to attack the problem by raising short term interest rates, and (only now) starting to reduce the Fed’s holdings of bonds. Massive buying of bonds is termed “Quantitative Easing” (QE), and its opposite is known as “quantitative tightening” or QT. QT can be accomplished by outright sales of bonds into the open market, or (as the Fed is doing) simply letting bonds mature and not replacing them with purchases of new bonds.

The specter of Fed tightening drove stock prices down all year, to a low in June. Then a new mantra began to circulate on Wall Street, that the Fed would relent at the first sign of economic slowdown, and hence would “pivot” back to easy money (low interest rate) policies. Stocks enjoyed 15% rise until stern speeches from the Fed in August convinced the Street that the Fed was going to stay the course until inflation is broken, and so stocks slumped back down to their June lows. Other major central banks like the European Central Bank and the Bank of England have likewise pledged tighter money policies in order to curb inflation.

However, stocks had a short-lived rally last Wednesday, when the Bank of England intervened in the markets by buying up long-term bonds. Aha, the central banks are caving at last! QE is back!!

It turns out that the reason the BOE intervened was not because of tight money conditions affecting general employment and income. Rather, there was a specific, technical reason. Many pension funds in the UK had entered into so-called “liability-driven investments” (LDIs), which involve interest rate swap agreements. I won’t try to explain the mechanical details of these beyond showing one figure:

Source: https://twitter.com/MacroAlf/status/1575542737725968385

In a stable world, these instruments allow pension funds to take money that they would have invested in boring, stable, low-interest bonds, and allocate it to (hopefully) higher-yielding investments such as stocks. But there is a huge catch, involving posting collateral, which in turn involves margin calls if the market price of long term bonds declines (as always happens when long-term interest rates go up).

The world has become less stable in the past six months, particularly since the Russian invasion of Ukraine. UK finances are shaky in the base case, and a proposal by the new prime minister for an unfunded tax cut that would exacerbate the budget deficit pushed the markets over the edge. Yields on British government bonds (“gilts”) surged, which would have triggered forced disastrous selling of assets (margin calls) by the pension funds at ever-lower prices.  This death spiral would have imperiled the solvency of these nationally-important funds. See here and here for more explanations.

Typical commentary:

…according to Cardano Investment’s Kerrin Rosenberg, most UK pension funds “would have been wiped out” were it not for the bond buying.

“If there was no intervention today, gilt yields could have gone up to 7% to 8% from 4.5% this morning and in that situation around 90% of UK pension funds would have run out of collateral,” Rosenberg told The Financial Times.

Will other central banks be forced to abandon money-tightening because of imperiled pension funds? The consensus seems to be probably not. The UK funds had a relatively high exposure to these derivatives, and British finances are in worse shape than most other major economies. That said, this is a cautionary example of the vulnerabilities of cleverly engineered financial instruments. In the end, there is no free lunch.