Photo Credit: Frugal Cafe/Reason.comPresident Barack Obama is adamant that he will not be held “hostage” by the Republicans in the House of Representatives, who are threatening not to raise the U.S. debt ceiling without some concessions on future spending and Obamacare. If the debt limit is not raised, allowing the Treasury Department to borrow more money, the federal government will default on some of the bills it owes in the next couple of weeks. Lots of commentators believe that such a default would have significant, if not devastating, downside economic effects.

Maybe so. But we should also want to consider the ways a relentlessly rising level of debt could damage our economic prospects. The debt ceiling for the United States is currently set at $16.7 trillion. In 2000, the U.S. national debt stood at $5.7 trillion. The amount of the U.S. national debt is now roughly the same size as the annual output of the economy. Is this a problem?

Yes, suggests recent research by numerous macroeconomists. Specifically, they find that a big public debt “overhang” likely slows down future economic growth for more than two decades. In other words, excessive national debt racked up now will make future Americans considerably poorer than they would have been otherwise.

Let’s start with a 2012 study in the Journal of Economic Perspectives, conducted by the Harvard economists Carmen Reinhart and Kenneth Rogoff and Morgan Stanley chief economist Vincent Reinhart. In that study, which looked at 22 advanced countries, the researchers identify in the years between 1800 and 2011 some 26 episodes lasting more than five years in which public debt to GDP ratios exceeded 90 percent. They argued that if the public debt-to-GDP ratio is greater than 90 percent for five or more years, then, on average, economic growth rates fall from an average of 3.5 percent to 2.3 percent annually, a drop of 1.2 percent. Even the fierce critics who pointed out a major error in the earlier work of Rogoff and Reinhart find that when the debt-to-GDP ratio is greater than 90 percent that subsequent economic growth averages 2.2 percent annually, falling from 4.2 percent when the ratio is below 30 percent.

Similarly, a 2010 working paper by the International Monetary Fund economists Manmohan Kumar and Jaejoon Woo looked at the effect that high public-debt-to-GDP ratios had on the economic growth of 38 advanced and emerging economies between 1970 and 2007. The study found evidence that surpassing a debt-to-GDP threshold of 90 percent has a significant negative effect on growth. The researchers also reported that a 10 percent increase in the debt-to-GDP ratio is associated with a 0.2 percent slowdown in annual real per capita GDP growth. As it happens, America’s debt-to-GDP ratio climbed from around 60 percent in 2003 to a projected 108 percent this year. If the IMF’s findings are accurate, that implies that future economic growth rates will be about one percent lower than they would otherwise have been. Kumar and Woo concluded that the chief cause for depressed economic growth is less investment in capital goods, which in turn produces a slowdown in labor productivity.

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