The number of people 45 and older who have been jobless for more than a year has quadrupled since 2007, accounting for nearly half of the 3.5 million Americans out of work for more than a year, according to the US ­Department of Labor.

“Historically, we’ve never seen anything that comes close to this; these numbers are unbelievably high,” said Andrew Sum, director of Northeastern University’s Center for Labor Market Studies. “And the longer you’re unemployed, the more likely you are to leave the labor force, and the more likely it’s an early retirement for you.”

This is not a sandy-beaches-and-sunsets type of retirement. After years of financial independence, many must lower standards of living, deplete savings, or rely on spouses’ earnings. The majority are older white men, according to the Labor Department, including many college-educated workers who rebounded from job losses earlier in their careers, only to see employment prospects dim in what should be their prime earning years.