DB schemes, by contrast, are meant to protect workers against aggregate longevity risk, but uncertainty about future improvements in life expectancy would affect these systems too. In fact, an unexpected increase in longevity would necessitate either increasing payroll contributions or the public debt. And in either case the burden would be borne entirely by the younger generations.
In other words, high longevity risk would translate into high “political” risk: pension promises might not be honoured, as the intergenerational pact on which they rest might prove socially and economically unsustainable, as well as intrinsically unfair.