After years of worrying about Europe's future, Cardinal Joseph Ratzinger of Germany put his hopes and fears on the record during a 2001 interview.

There had been hints. German journalist Peter Seewald noted an old quote in which Ratzinger said the church would be "reduced in its dimensions, it will be necessary to start again." Had the leader of Rome's Congregation for the Doctrine of the Faith changed his views?

"Statistical data shows irrefutable tendencies," replied Ratzinger. "The mass Church may be something lovely, but it is not necessarily the Church's only way of being.

"The Church of the first three centuries was small, without being, by this fact, a sectarian community. On the contrary, it was not closed in on itself, but felt a great responsibility in regard to the poor, the sick."

Four years later, this bookish cardinal became Pope Benedict XVI, serving until his stunning resignation in 2013 -- the first pope to resign in 600 years. Meanwhile, waves of change have continued to rock Eastern and Western Europe.

Now, the Benedict XVI Centre for Religion in Society, based at St. Mary's University in London, has released a study showing that Christianity is no longer Europe's default religion, especially among the 16- to 29-year-olds who are its future. "Europe's Young Adults and Religion," was produced with the Institut Catholique de Paris, analyzing data from 22 countries, drawn from the 2014-2016 European Social Survey.

In 18 of these countries "fewer than 10 percent of all 16-29 year-olds attend religious services at least weekly. And in 12 of them, over half say that they have 'no religion,' " noted Stephen Bullivant, the report's author and director of the Benedict XVI Centre, in email exchanges with Rod Dreher of The American Conservative.

"These are all countries in Europe, the very heart of Christendom, where Christianity (albeit in several forms) has been reliably passed on from generation-to-generation for the best part of 2000 years. And now, in the space of just a couple of generations, that's largely stopped in many places."

The key, he said is that "nominal" or "cultural" faith doesn't pass from one generation to another.