85% of public pensions could fail in 30 years

Here's a scary retirement prediction: 85 percent of public pensions could fail in 30 years.

That's according to the largest hedge fund firm in the world, Bridgewater Associates, which runs $150 billion for pensions and other institutions like endowments and foundations.

Public pensions have just $3 trillion in assets to cover liabilities that will balloon to $10 trillion in future decades, Bridgewater said in a client note last week obtained by USA Today.

To make up the difference, the firm said pensions will need to earn about 9 percent per year on their investments. But Bridgewater estimates pension funds are more likely to make 4 percent. If that's true, the vast majority—85 percent—of retirement systems will run out of money because they will continue to pay out more than they take in.

The report comes as pensions wrestle with what rates of return to assume given their implications on future financial health.