Over the past few generations, public employees have been promised generous pensions, but now the bill is coming due just as employees are ready to cash in and there’s hardly anyone to pay up.

The public pension debt is a tsunmani that no one wants to think about, but Moody’s places the rising tide at $2 trillion. It makes up more than half of all outstanding state and local bond debt.

The recent economic downturn contributed significantly, but the pension shortfall has been building for years.

Perhaps biggest concern is that we have a shrinking workforce unable to generate enough income to pay for both current and future retirees. Between rising long-term unemployed, rising part-time versus fulltime workers, and growing numbers of those who have entirely dropped out of the job market, there are not enough taxpaying workers who can pay into pension fund savings.

However, when you think about it, it’s quite an unfair system. Young workers, for example, are forced by government to pay into this system which, given the current trajectory, may not be around for them to benefit from. So while it’s billed as paying into your future, we really have pay-as-you-go.

CNBC reports:

In less than a decade, that shortfall has tripled to at least $2 trillion—more than half of all outstanding state and local bond debt, according to a report by Moody's Investors Service.

Moody's looked at the unfunded liabilities of the 25 biggest public retirement systems, which cover 40 percent of the $5.3 trillion in total U.S. public pension plan assets.

But the pension shortfall had been building well before the downturn—and has been made worse by state and local government's shortchanging annual fund contributions…

States and cities have also used accounting gimmicks to mask the widening shortfall, including "asset-smoothing" that lets them spread out the impact of the market downturn. They've also used rosy scenarios to inflate their estimated investments.

Pension funds are also getting hammered by demographic forces that show no signs of easing. Widespread state and local job cuts since the Great Recession have shrunk the pool of active workers paying into pension fund savings—even as the pool of current retirees drawing benefits is living longer.

The question is what should be done? No more kicking the can down the road for starters. As CNBC explains, many states are simply not paying their bills in full – underfunding the annual contributions at 90 percent or less. While that may free up cash for other immediate priorities it contributes to the growing pension debt and pushes the magnified pain further down the road.

Some lawmakers have sweetened retirees' benefits during good times. At this point, even if our economy comes roaring back and we reach full employment, it’s no time to win votes with new promises. That’s the time to hunker down and pay down this debt, even stowing something away in case of an (inevitable) economic downturn.

In addition, pensions must be reformed going forward. We can’t expect to offer new and future public workers the same levels of pensions as their parents. Otherwise we are just perpetuating failing policies that keep us as a nation straddled with unnecessary debt.

These numbers about how dire the situation is are eye-opening. Hopefully, Congress, governors, and state lawmakers are paying attention.