What other power but civil government  has the authority to make this prudential judgement? 

Pope Francis says capital punishment “is per se contrary to the Gospel.”  A statement no pope, including John Paul II, has taught. He went on that “no one ought to be deprived… of life .... no matter how serious the crime that has been committed, the death penalty is inadmissible because it is an attack on the inviolability and the dignity of the person,” and that traditional arguments in defense of capital punishment “now appear clearly contrary to the new understanding of Christian truth.” He wants “a more adequate and coherent treatment” of the death penalty with a more negative attitude toward it than the Catechism issued by John Paul II.  The Catechism already includes a prudential judgment to the effect that under contemporary circumstances capital punishment should be “very rare, if not practically nonexistent.”

How is this not a new teaching in contradiction to John Paul's?