Alex Tabarrok at Marginal Revolution tries to give Senator Lieberman an assist:
Brad DeLong and Paul Krugman are taking Joe Lieberman and others to task for asserting that the cost of fixing the social security problem increases at $600 billion a year. I agree that Lieberman is confusing an increase in the nominal present value of the debt with an increase in the cost of fixing social security but in correcting Lieberman both DeLong and Krugman meander towards the opposite error - that the costs of fixing social security is not increasing.
But almost inevitably a fix to social security will involve tax increases and the longer we wait the larger the costs of those increases will be. The technical explanation is that deadweight loss increases more than proportionately with an increase in taxes. The common sense explanation is that you don't want to take all your hits at once - instead, if you must take a hit, it's best to spread it out over time. Thus, the sooner we deal with the problem the lower the total costs will be. Lieberman's message is
correct, even if the details are wrong.
Yes, the $600 billion number is not the right number. For the right number and the right argument, I conjure my first post on Social Security from last October:
At present, the Social Security actuaries project an unfunded obligation of $10.4 trillion in the Old-Age, Survivors, and Disability Insurance (OASDI) program. This number comes directly from the 2004 Trustees Report released in March. (See Section IV.B.5 and Tables IV.B.7 and IV.B.8 in particular.) This is the present value of the projected payments less the present value of projected revenues for the system over the infinite horizon. It is the most comprehensive way to measure the hole in the system's finances.
Note that this is the unfunded part of the obligations--it is over and above all of the payroll taxes (12.4 percent of taxable payroll) and income taxes on benefits that go to support the program under current law. If this gap were to be closed through payroll taxes, it would require them to be raised by 3.5 percentage points, immediately and permanently, with the additional surpluses over the next few decades saved (in Treasury bonds) to finance annual deficits that are projected to grow to about 6 percentage points of payroll over the next 75 years.
This $10.4 trillion unfunded obligation is sometimes referred to as implicit debt, to distinguish it from the federal government's explicit debt issued in the form of Treasury bills, notes, and bonds held by the public. At present, implicit debt from Social Security and Medicare is several times larger than the government's explicit debt. Is having so much implicit debt a problem? I think so, and the reason is that, just like explicit debt, we accrue interest on implicit debt.
[...]
So if we have an implicit debt of $10.4 trillion, and the real interest rate is 3 percent, then next year, the implicit debt will grow by 0.03*10.4 trillion = $312 billion, up to $10.7 trillion, if the assumptions underlying the projection stay the same. Why does this matter? Primarily, it matters because both the President and Senator Kerry have repeatedly stated (see the two speeches in Pennsylvania linked above) that they will not cut benefits for those at or near retirement age. (The Senator's statement may be even more encompassing, including benefits at any time in the future. I cannot tell for sure from his public statements.) This, in turn, means that each year that elapses without reform causes the burden of financing the unfunded obligations to be shifted away from one more birth cohort that crosses the threshold of being "at or near retirement." The more we wait, the larger the burden on future
generations, and the higher that 3.5 percentage point surtax would have to climb.
The $10.4 trillion is about 90 percent of current GDP. In a later post, I made a rough calculation that if we waited until 2042 (the projected date of trust fund exhaustion), the implicit debt would grow (at the 3 percent real interest rate), to about $32 trillion, which would be about 141 percent of that year's (much larger GDP). So even if taxable payroll didn't fall as a share of GDP, the surtax applied in perpetuity would have to increase by a factor of 141/90, or from 3.5 to 5.5 percentage points.
The issue that Alex is pointing out is tax smoothing: for efficiency reasons, it is better to have a surtax rate that is steady at 3.5 percent rather than one that is 0 for 38 years and then jumps to 5.5 percent. The issue is, for me, less about tax smoothing and more about the intergenerational fairness of consigning future generations to pay higher payroll tax rates. We shouldn't be doing that--in Social Security, the General Fund, or Medicare.