NEW HAVEN โ€“ Predicting the next crisisโ€”financial or economicโ€”is a foolโ€™s game. Yes, every crisis has its hero who correctly warned of what was about to come. And, by definition, the hero was ignored (hence the crisis). But the record of modern forecasting contains a note of caution: Those who correctly predict a crisis rarely get it right again.

The best that economists can do is to assess vulnerability. Looking at imbalances in the real economy or financial markets gives a sense of the potential consequences of a major shock. It doesn’t take much to spark corrections in vulnerable economies and markets. But a garden-variety correction is far different from a crisis. The severity of the shock and the degree of vulnerability matter: Big shocks to highly vulnerable systems are a recipe for crisis.

In this vein, the source of vulnerability that I worry about the most is the overextended state of central-bank balance sheets. My concern stems from three reasons.

First, central banksโ€™ balance sheets are undeniably stretched. Assets of major central banksโ€”the U.S.ย Federal Reserve, theย European Central Bankย and theย Bank of Japanโ€”collectively stood at $14.5 trillion in November 2019, which is down only slightly from the peak of around $15 trillion in early 2018 and more than 3.5 times the pre-crisis level of $4 trillion. A similar conclusion comes fromย scaling assetsย by the size of their respective economies: Japan leads the way at 102 percent of nominal GDP, followed by the ECB at 39 percent and the Fed at a mere 17 percent.

Second, central banksโ€™ balance-sheet expansion is essentially a failed policy experiment. Yes, it was successful in putting a floor under collapsing markets over a decade ago, in the depths of the crisis in late 2008 and early 2009. But it failed to achieve traction in sparking vigorous economic recovery.

Central banks believed that what worked during the crisis would work equally well during the recovery. That didnโ€™t happen. The combined nominal GDP of the United States, eurozone and Japan increased byย $5.3 trillionย from 2008 to 2018, or only about half their central banksโ€™ combined balance-sheet expansion of $10 trillion in over the same period. The remaining $4.7 trillion is the functional equivalent of a massive liquidity injection that has been propping up asset markets over most of the post-crisis era.

Third, steeped in denial, central banks are once again upping the ante on balance-sheet expansion as a means to stimulate flagging economic recoveries. The Fedโ€™s late 2018 pivot led the way, first reversing the planned normalization of its benchmark policy rate and then allowing its balance sheet to grow again (allegedly forย reserve managementย purposes) following steady reductions from mid-2017 through August 2019. Asset purchases remain at elevated levels for the BOJ as a critical element of the โ€œโ€ reflation campaign. And the recently installed ECB president,ย Christine Lagarde, the worldโ€™s newest central banker, was quick to goย on the recordย stressing that European monetary authorities will โ€œturn (over) each and every stoneโ€โ€”which presumably includes the balance sheet.

So why is all this problematic? After all, in a low-inflation era, inflation-targeting central banks seemingly have nothing to fear about continuing to err on the side of extraordinary monetary accommodation, whether conventional (near zero-bound benchmark policy rates) or unconventional (balance-sheet expansion). The problem lies, in part, with theย ย itselfโ€”a longstanding, but now inappropriate, anchor for monetary policy. The mandate is woefully out of sync with chronically below-target inflation and growing risks to financial stability.

The potential instability of the U.S. equity market is a case in point. According to theย widely cited metricsย of Nobel laureate economistย Robert Shiller, equity prices relative to cyclically adjusted long-term earnings currently are 53 percent above their post-1950 average and 21 percent above the post-crisis average since March 2009. Barring a major reacceleration of economic and earnings growth or a new round of Fed balance-sheet expansion, further sharp increases in U.S. equity markets are unlikely. Conversely, another idiosyncratic shockโ€”or a surprising reacceleration of inflation and a related hike in interest ratesโ€”would raise the distinct possibility of a sharp correction in an overvalued U.S. equity market.

The problem also lies in weak real economies that are far too close to their stall speed. Theย International Monetary Fundย recently lowered its estimate for world GDP growth in 2019 to 3 percentโ€”midway between the 40-year trend of 3.5 percent and the 2.5 percent threshold commonly associated with global recessions. As the year comes to a close, real GDP growth in the U.S. is tracking below 2 percent, and the 2020 growth forecasts for the eurozone and Japan are less than 1 percent. In other words, the major developed economies are not only flirting with overvalued financial markets and still relying on a failed monetary-policy strategy, but they are also lacking a growth cushion just when they may need it most.

In such a vulnerable world, it would not take much to spark the crisis of 2020. Notwithstanding the risks of playing the foolโ€™s game, three โ€œPsโ€ are at the top of my list of concerns: protectionism, populism and political dysfunction. An enduring tilt toward protectionism is particularly troubling, especially in the aftermath of aย ย between the U.S. and China. Prime Minister Narendra Modiโ€™s โ€œโ€ crusade in India could well be the most disturbing development in a global swing toward populism. And the greatย American impeachmentย saga takes Washingtonโ€™s political dysfunction further into uncharted territory.

Quite possibly, the spark will be something elseโ€”or maybe there wonโ€™t be any shock at all. But the diagnosis of vulnerability needs to be taken seriously, especially because it can be validated from three perspectivesโ€”real economies, financial asset prices and misguided monetary policy. Throw a shock into that mix and the crisis of 2020 will quickly be at hand.

Stephen S. Roach, a faculty member at Yale University and former chairman of Morgan Stanley Asia, is the author of Unbalanced: The Codependency of America and China.

ยฉ Project Syndicate, 2020