I was on PBS’ NewsHour last night, talking austerity. I’m against it. Ken Rogoff from Harvard was also on, and he’s actually against it too. One point of disagreement came up, though, when I made the argument that public debt incurred when the economy is depressed causes no economic damage (in fact, it acts instead as a useful palliative).

Rogoff disagreed in principle and then said something kind of startling—that increases in deficits and debt could lead to incomes in the near-ish future (i.e., less than 30 years from now) that are “20 percent lower.”

I’m assuming this claim has some relation to a Congressional Budget Office estimate of the effect of one particular fiscal scenario (the “alternative fiscal scenario,” or AFS) that projects the effects of large increases in budget deficits in coming decades on economic growth (see table below from the CBO report (p. 28)). The mechanism is that rising deficits increase interest rates which lead to lower private investment and a stronger dollar, which leads in turn to higher trade deficits and rising foreign debt.

Set aside for a second whether or not there are some problems with these calculations—both in relying on the AFS to make predictions and in how to apportion the impact of higher interest rates between crowded-out domestic investment versus increased trade deficits. The more salient point is simply that there is nothing in the CBO analysis that rebuts my larger point: Potential damage from increased public debt does not materialize when this debt is taken on when the economy is depressed. Here’s the CBO on the issue (p. 21 in the linked report):

“… when the economy has substantial unemployment and unused factories, offices, and equipment, federal budget deficits—and thus additional debt—generally boost demand, thereby increasing output and employment relative to what would occur with a balanced budget. … CBO’s estimates in this chapter [ed: estimates about the output-depressing effects of budget deficits and extra public debt] do not take those short-run effects on demand into account. Indeed, the estimates reflect the assumption that over the long run, output is always at its potential level”

In short, the potential output-depressing effects stemming from budget deficits that the CBO is estimating only hold when “output is at its potential level.” Or to say it another way, the exact way I said it earlier, extra public debt incurred when the economy is depressed (i.e., output is not “at its potential level”) causes no economic damage.

And in fact, when extra public debt is incurred when the economy is depressed, the boost it gives (if spent wisely) to economic output can easily be large enough to actually reduce overall the overall debt/GDP ratio by boosting the denominator and by spurring enough additional tax collections to actually self-finance part of the extra debt. How are people so sure that the extra debt incurred in recent years hasn’t led to any of the downsides from crowding out or upward pressure on the value of the dollar? Simple—interest rates have not risen. And remember, the entire economic chain wherein incurring public debt leads to crowding-out and trade deficits is through upward pressure on interest rates. And, since the depressed economy is putting ferocious downward pressure on interest rates, there is no damage done.

Until the economy recovers and this downward pressure on interest rates relents, additional increments of public debt do not hurt, and scare-stories about the 20 percent income loss possible 25 years from now because of deficits do not change this calculus at all.