Pension problems exacerbated by low yields

WSJ has an interesting piece on the difficulties that low yields are creating for defined benefit pension plans.  

Pension officials and government leaders are left with vexing choices. As investors, they have to stash away more than they did before or pile into riskier bets in hedge funds, private equity or commodities. Countries, states and cities must decide whether to reduce benefits for existing workers, cut back public services or raise taxes to pay for the bulging obligations.

Students will recognize this problem from Chapter 5, where managers of defined benefit pension plans are using discount rates equal to 7.5%, when the real rates of return are much lower.

As the following graph demonstrates, this problem is not limited to the US: