What is Longevity risk, and how to model it under DC and DB pension plans?
While it seems surprising how longevity can be a risk, it becomes obvious if you look at the financial implications. For an individual longevity risk is the chance of outliving your retirement savings. For pension plans or more generally any financial institution guaranteeing individuals lifelong income, it is the deviation, due to increased survival or decreased mortality, of initial projections of annuities from actual numbers.
There is a great variety of ways to model, measure and mitigate longevity risk. A good introduction is "FINANCIAL ASPECTS OF LONGEVITY RISK" published by the Staple Inn Actuarial Society.