China's own DEBT BOMB Six years ago, Chinese Premier Wen Jiabao cautioned that China's economy is "unstable, unbalanced, uncoordinated and unsustainable." China has since doubled down on the economic model that prompted his concern. Mr. Wen spoke out in an attempt to change the course of an economy dangerously dependent on one lever to generate growth: heavy investment in the roads, factories and other infrastructure that have helped make China a manufacturing superpower. Then along came the 2008 global financial crisis. To keep China's economy growing, panicked officials launched a half-trillion-dollar stimulus and ordered banks to fund a new wave of investment. Investment has risen as a share of gross domestic product to 48%â€”a record for any large countryâ€”from 43%. Even more staggering is the amount of credit that China unleashed to finance this investment boom. Since 2007, the amount of new credit generated annually has more than quadrupled to $2.75 trillion in the 12 months through January this year. Last year, roughly half of the new loans came from the "shadow banking system," private lenders and credit suppliers outside formal lending channels. These outfits lend to borrowersâ€”often local governments pushing increasingly low-quality infrastructure projectsâ€”who have run into trouble paying their bank loans. Since 2008, China's total public and private debt has exploded to more than 200% of GDPâ€”an unprecedented level for any developing country. Yet the overwhelming consensus still sees little risk to the financial system or to economic growth in China.That view ignores the strong evidence of studies launched since 2008 in a belated attempt by the major global financial institutions to understand the origin of financial crises. The key, more than the level of debt, is the rate of increase in debtâ€”particularly private debt. (Private debt in China includes all kinds of quasi-state borrowers, such as local governments and state-owned corporations.) On the most important measures of this rate, China is now in the flashing-red zone. The first measure comes from the Bank of International Settlements, which found that if private debt as a share of GDP accelerates to a level 6% higher than its trend over the previous decade, the acceleration is an early warning of serious financial distress. In China, private debt as a share of GDP is now 12% above its previous trend, and above the peak levels seen before credit crises hit Japan in 1989, Korea in 1997, the U.S. in 2007 and Spain in 2008. The second measure comes from the International Monetary Fund, which found that if private credit grows faster than the economy for three to five years, the increasing ratio of private credit to GDP usually signals financial distress. In China, private credit has been growing much faster than the economy since 2008, and the ratio of private credit to GDP has risen by 50 percentage points to 180%, an increase similar to what the U.S. and Japan witnessed before their most recent financial woes.The bullish consensus seems to think these laws of financial gravity don't apply to China. The bulls say that bank crises typically begin when foreign creditors start to demand their money, and China owes very little to foreigners. Yet in an August 2012 National Bureau of Economic Research paper titled "The Great Leveraging," University of Virginia economist Alan Taylor examined the 79 major financial crises in advanced economies over the past 140 years and found that they are just as likely in countries that rely on domestic savings and owe little to foreign creditors. The bulls also argue that China can afford to write off bad debts because it sits on more than $3 trillion in foreign-exchange reserves as well as huge domestic savings. However, while some other Asian nations with high savings and few foreign liabilities did avoid bank crises following credit booms, they nonetheless saw economic growth slow sharply. Following credit booms in the early 1970s and the late 1980s, Japan used its vast financial resources to put troubled lenders on life support. Debt clogged the system and productivity declined. Once the increase in credit peaked, growth fell sharply over the next five years: to 3% from 8% in the 1970s and to 1% from 4% in the 1980s. In Taiwan, following a similar cycle in the early 1990s, the average annual growth rate fell to 6%. Even if China dodges a financial crisis, then, it is not likely to dodge a slowdown in its increasingly debt-clogged economy. Through 2007, creating a dollar of economic growth in China required just over a dollar of debt. Since then it has taken three dollars of debt to generate a dollar of growth. This is what you normally see in the late stages of a credit binge, as more debt goes to increasingly less productive investments. In China, exports and manufacturing are slowing as more money flows into real-estate speculation. About a third of the bank loans in China are now for real estate, or are backed by real estate, roughly similar to U.S. levels in 2007.For China to find a more stable growth model, most experts agree that the country needs to balance its investments by promoting greater consumption. The catch is that consumption has been growing at 8% a year for the past decadeâ€”faster than in previous miracle economies like Japan's and as fast as it can grow without triggering inflation. Yet consumption is still falling as a share of GDP because investment has been growing even faster. So rebalancing requires China to cut back on investment and on the rate of increase in debt, which would mean accepting a rate of growth as low as 5% to 6%, well below the current official rate of 8%. In other investment-led, high-growth nations, from Brazil in the 1970s to Malaysia in the 1990s, economic growth typically fell by half in the decade after investment peaked. The alternative is that China tries to sustain an unrealistic growth target, by piling more debt on an already powerful debt bomb. Mr. Sharma is head of emerging markets at Morgan Stanley Investment Management and author of "Breakout Nations: In Pursuit of the Next Economic Miracles" (Norton, 2012).