The problem with budgeting 75 years into the future is that you end up with a lot of numbers that are much more meaningful to actuaries than to other living people

Wanna scare somebody about America's debt on the eve of the Fiscal Cliff? I mean, really scare somebody? Here's a trick. Don't talk about the debt. Talk about "unfunded liabilities."

The U.S. national debt comes out to about $16 trillion today. That's something. But it's nothing compared to the extra $87 trillion in unfunded liabilities to Social Security, Medicare, and federal pensions. Here's how that works. If you add up all of the U.S. government's promises to pay retirement and health care benefits for the next 75 years and subtract the projected tax revenue dedicated to those programs over the next 75 years, there is a gap. A $87 trillion gap -- in addition to a $16 billion hole.

"Why haven't Americans heard about the titanic $86.8 trillion liability from these programs?" Chris Box and Bill Archer ask in the Wall Street Journal. The authors blame the U.S. government for using shoddy accounting and for misleading the American public on their finances. In fact, the most misleading thing about that $87 trillion is the way the figure is often used in the media.

(1) That's not our debt. Our $16 trillion in debt and our $87 trillion in "unfunded liabilities" represent two very different ideas: real past promises and projected future promises. Real past promises are, well, very real. We have to pay back our debt. Failing to do it would be an illegal and disastrous default. Unfunded liabilities are future promises, and, since they're not as real, we can change them whenever we want without destroying ourselves. For example, raising the taxable income ceiling and slowing the growth of benefits could reduce the Social Security gap to zero tomorrow.

And that's if there is a Social Security "gap" to begin with. Technically, it's not legal for Social Security to have "unfunded liabilities" since it can only pay as many benefits as it receives in earmarked taxes. Both it and Medicare hospital insurance are prohibited from spending money they haven't collected from specific revenue dedicated to their programs (i.e.: payroll taxes). It is impossible for either to technically be "unfunded", since they cannot legally outspend their funding.

(2) 75-year projections are scarier than they are informative. Seventy-five-year projections always sound gargantuan because, well, they're calculated over three-quarters of a century, which is an awfully long time to count anything. But here's the flip side: In 75 years, our economy will be massive. Growing slowly at a 2% annual average, our GDP would be $66 trillion in today's dollars in 2087. That's an incomprehensibly big number, too. Once you run out any number over 75 years, the mind starts to boggle. That's good for scaring people with mind-boggling numbers, but it's not so good for informing. When Republicans say unfunded liabilities come out to $520,000 per U.S. household, they're taking a figure from 2087 and dividing it over a 2012 population to exaggerate. Scary, to be sure, but not very informative.

(3) Projections can change fast.  An unfunded liability is a projection, and projections shift all the time for two big reasons: (1) Circumstances change and (2) laws change. Let's take circumstances first: The shortfall in Medicare and Social Security is exquisitely sensitive to just about every demographic trend you can imagine, including longevity, immigration, income growth, and birth rates. Furthermore, it assumes that seven decades of innovation will do nothing to change the rate of health care inflation, which is a brave assumption. We know next to nothing about how medical inflation will change after this decade. The fact that actuaries pretend to know the future doesn't make them oracles. It just makes them dutiful actuaries.

Now, about our laws. Strictly speaking, the U.S. doesn't have an entitlement problem, or even a Medicare problem. Rather, we have a health care cost problem -- medical insurance and hospital costs and so on are getting expensive faster than our ability to pay for them. Medicare and Medicaid are part of this big expensive system. If we cut these programs without changing the system, we won't be "saving" money, so much as shifting costs to old folks, who will be forced to pay much more for their health care, or else see much worse coverage.

What can we do? We can get quantitative, and we can get creative. Getting quantitative means finding the fairest ways to raise revenue and cut benefits to close the foreseeable Medicare gap. Getting creative means firing a quiver of ideas at the health care inflation monster, like exchanges and advisory boards and innovation centers and laws nudging insurers to pay for health outcomes rather than gratuitous services.

Closing this liability gap -- whether it's $87 trillion or $8 trillion -- will require patience. The bad news is that none of these measures to fix our real problem (health care costs) will be easy, few of them will be initially popular, and most of them might not work. The good news is we have 75 years.