The former pontiff has been chronicled in Ultime Conversazioni, or "Last Conversations", which was released today.
According to excerpts of the book published in Corriere della Sera, Benedict warned of the "de-Christianisation" of the continent, adding: "Consequently the Church must find a new form of presence, it must change its way of presenting itself.
"Epochal upheavals are underway."
The former pope also admitted in Last Conversations that managing was not his "strong suit" while he was in office but that he did not feel like a failure.
"My weakness is perhaps the lack of resolve to govern and make decisions. In truth I am more of a professor who reflects and mediates on spiritual questions," he said.
The book also includes the story of how the pontiff quashed a so-called gay lobby within the Vatican, a group he claims were self-interested.
Benedict XVI became the first pope to resign from the papacy in 600 years, citing health problems.
By Megan Howe