NEW YORK (CNNMoney.com) -- Letting U.S. debt grow unabated is often framed as an unforgivable burden to heap on one's grandchildren.
But there are plenty of reasons today's parents might be concerned for themselves and their kids.
If Congress doesn't craft a plan to address long-term fiscal shortfalls after the economy recovers, potential problems could arise sooner rather than later, debt experts say.
Slower economic growth: After examining data from dozens of countries over the past two centuries, economists Carmen Reinhart and Kenneth Rogoff found a connection between high debt and reduced economic growth. Specifically, they found that when a nation's gross debt reaches 90% of its economy, it often loses about one percentage point of growth a year.
U.S. gross debt -- currently $13 trillion -- will hit the 90% threshold this year. Gross debt includes money owed to those who hold U.S. bonds and money owed to government trust funds such as Social Security.
Reinhart has said the relationship between high debt and low growth is "self-feeding." Low growth ravishes government revenue and increases the need to borrow. More borrowing builds debt. Higher debt increases pressure to tighten fiscal policies in order to reduce the risk that investors lose confidence in the country. But tighter policies can slow economic growth.
One percentage point lower growth may not seem huge. But it's equal to roughly a third of the average annual GDP forecast over the next decade.
And slower growth can reduce the number of jobs created, which in turn can hold down household incomes.
High interest payments: Interest rates are still very low and may continue to be as the debt crisis in Europe makes the United States a more attractive safe haven for investors.
That means the government can borrow on the cheap right now. But rates will rise as the world economy recovers. By 2020, annual interest owed on U.S. debt will approach $1 trillion, or roughly 21% of projected federal revenue for that year, according to Congressional Budget Office estimates.
Interest rates may rise further than expected if credit rating agencies or investors start to doubt U.S. resolve to rein in the growth in debt. And that would jack up the cost of borrowing for businesses and consumers.
Ironically, some debt experts would almost prefer that rates rise so there will be more urgency to deal with the debt situation. It might hurt, but not as much as if rates stay very low for a long time -- planting the seeds for the next credit bubble and bust when U.S. debt levels are that much higher.
Less government support: The more debt the government accrues, the more it will pay in interest and the less it will have to spend on the basic services Americans expect from their government.
Spending for everything from education to infrastructure and defense could be compromised. And, many argue, not being able to make strategic investments in these areas can weaken the country competitively.
Also, the government will be hamstrung in responding to emergencies such as natural or man-made disasters, terrorist attacks or future economic downturns.
Inflation: There don't appear to be any official signs of inflation brewing today. But throughout U.S. history, high levels of debt have usually brought high rates of inflation, Reinhart and Rogoff found.
Some economists -- including Kansas City Federal Reserve Bank President Thomas Hoenig -- have said they are concerned about what could happen if the United States faces a debt crisis. In such a case, the Federal Reserve may cave to political pressure to let inflation rise, which reduces the real value of the country's debt but also devalues people's savings and income.
Harsh choices: No one can say when or even if a debt crisis will occur. But lawmakers will tempt fate if they wait too long to address the imbalances on the U.S. balance sheet, fiscal experts say.
Fiscal experts believe it's entirely possible that, absent action, the United States would experience a debt crisis within the next 10 to 20 years.
"Most believe it would happen much sooner than 20 years," said Maya MacGuineas, president of the bipartisan Committee for a Responsible Federal Budget. Many believe it could happen within the next five to 10 years, she said.
And waiting too long would force lawmakers to make much more draconian and abrupt changes than they would otherwise.
Experts are increasingly convinced that Congress won't act until a true crisis is on the U.S. doorstep -- for two reasons. The first is the sharp partisan divide. The second is that no politician likes to run on promises to implement difficult and unpopular measures.
So until there's sufficient public support for debt reduction, don't expect to see much political will for it.
"Like the proverbial frog that fails to jump out of the soup pot as the temperature slowly rises, Americans seem terrifyingly unwilling to act until the pain of debt can no longer be ignored," Syracuse University professor Len Burman wrote in a recent essay. "As the frog learns in its final moments, by then, it's too late."
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