Pope Benedict, in an encyclical released on Friday, said atheism was responsible for some of the "greatest forms of cruelty and violations of justice" in history.
The 75-page "Spe Salvi", which takes its Latin title from a quote by St Paul (in hope we were saved), is an appeal to a pessimistic world to find strength in Christian hope.
In the second encyclical of his papacy, Benedict urges Christians to put their hope for the future in God and not in technology, wealth or political ideologies.
Atheism could be regarded by some as a "type of moralism", particularly in the 19th and 20th centuries, to protest against the injustices of the world and world history, he said.
Reciting arguments made by atheists, he said: "A world marked by so much injustice, innocent suffering and cynicism of power cannot be the work of a good God. A God with responsibility for such a world would not be a just God, much less a good God."
History has proven wrong ideologies such as Marxism which say humans had to establish social justice because God did not exist, the Pope wrote.
"It is no accident that this idea has led to the greatest forms of cruelty and violations of justice," the Pope said. Such a concept was grounded in "intrinsic falsity".
Marxism, the Pope wrote, had left behind "a trail of appalling destruction" because it failed to realise that man could not be "merely the product of economic conditions".
