EDMOND — “We have lent a huge amount of money to the U.S., so of course we are concerned about the safety of our assets. Frankly speaking, I do have some worries,” — Chinese Premier Wen Jiabao, March 12, 2009.

In some important ways economists are a lot like seismologists. Seismologists know, for example, that California will be struck by more major earthquakes in its future. While they do not know when the next major earthquake will strike, there is no doubt that a major earthquake is coming.

Economists too, study earthquakes — economic earthquakes. Economists knew that the stock market bubble of the 1990s, and housing bubble earlier this decade were not sustainable. Economists knew that eventually those bubbles would burst, and that the U.S. economy would suffer as a result.

Economists also knew that Fannie Mae and Freddie Mac were ticking time bombs. Those two governmental-sponsored enterprises used their unique connection to the federal government to borrow incredible sums of money at below-market rates and grow to an enormous size (once having purchased nearly one-half of all mortgages in the U.S.). Yet this unique connection to the federal government meant that U.S. taxpayers were on the hook for any losses.

But there is another problem, a potentially more dangerous problem, that economists are fretting about now. That problem is the rising national debt. In 2001 the U.S. national debt — technically the debt held by the public was $3.3 trillion. By last September, the national debt had risen to $5.8 trillion. As of this last Wednesday, the debt exceeds $6.6 trillion. In other words in just the past eight years we have doubled the amount of debt that took our nation 225 years to amass. Unfortunately, the sea of governmental red ink will keep flowing. The nonpartisan Congressional Budget Office estimates that we will add another $4 trillion of debt in the next 10 years, and Congress still keeps considering plans to add even more.

With all this debt it is easy to become numb to the numbers. After all, what’s another $4 trillion among friends?

To see why this growing mountain of debt is so worrisome to economist, we must remember that whenever the government runs a budget deficit it must borrow money to pay its obligations. While historically that meant borrowing money from U.S. savers, that is increasingly not the case today. According to the U.S. Treasury, as of Dec. 31 more than $3 trillion of our debt was held by foreign governments and individuals including $727 billion to China, $626 billion to Japan, $186 billion to oil exporting nations and $116 billion to Russia.

During the past few decades these governments have been willing to lend money to the U.S. government because U.S. government debt is considered one of the safest investments in the world. But there is no guarantee that this will continue. In fact, the deeper the U.S. government goes into debt, the greater the risk to the lenders. Consequently, if we keep adding more and more debt there will come a time when other nations no longer want to lend to us — they will find a better investment instead. Comments from the Chinese premier this week signal that this shift may not be far off.

When this happens, the U.S. government will need to offer higher returns (higher interest rates) to attract sufficient funds. But higher interest rates raise the cost of borrowing for all businesses and consumers, not just the government. With higher borrowing costs consumers cut back on their spending and firms cut back on their investments. Essentially, larger debts today inevitably lead to slower economic growth and lower incomes in the future.

The economic news from the past six months has been the grimmest seen in my lifetime. We have had the bursting of the housing bubble, the emergence of zombie banks, the collapse of the U.S. auto industry and the plummeting of consumer confidence all contributing to a deep recession that already has cost 4.4 million jobs. But thanks to our insatiable appetite for debt, the grimmest economic news of our children’s lifetime is still to come.

MICKEY HEPNER is an associate professor of economics at the University of Central Oklahoma.