Hmm. Pensions are obligated to deliver a defined benefit in dollar terms, or try their best to do so. In a world where interest rates are being pushed lower every year, pensions are basically forced to move to riskier assets to deliver the same nominal return. (This is, in fact, one of the main points of lower interest rates.)

Because pensions are not marketable instruments, it's also not possible for these risks to be priced in. (If a bond had, say, a 50% chance of default, its price on the market would also decrease, pushing up its effective yield.

It seems pensions are more of an instrument that is doomed to fail, and expecting them to hold up to their promises is going to lead to a lot of pain for either retirees, or the current and future workers supporting them.