Pope Francis' expected encyclical letter on the environment is raising concerns among traditionalists that it could herald an incremental shift in the church's attitude toward the sanctity of life, according to John Allen, associate editor of Crux.

Encyclicals exhort the faithful to constancy but do not necessarily have binding force on believers, according to the Catholic Encyclopedia. They are, however, seen as "the most developed form of papal teaching," Allen wrote.

Popes have regularly spoken about conservation and the environment, though this would be the first encyclical in church history focused squarely on climate change, Allen wrote.

A recent poll of believers in England showed that a third of Catholics would shift to a greener lifestyle based on an official statement from the pope on climate change, the Independent reported.

Francis believes that climate change is mostly man-made and that the Catholic Church needs to lend its influence to cleaning up the environment. Allen quoted the pope as saying, "God always forgives, man sometimes forgives, but nature never forgives."

The encyclical is expected in June.

Allen cited veteran Vatican observer Riccardo Cascioli as saying: "The road the Church is heading down is precisely this: To quietly approve population control while talking about something else."

The issues of "environmentalism and population control are intrinsically linked," wrote Allen in summarizing Cascioli's view. He believes secular environmentalism has penetrated the church at its most senior levels.

"Up to this point, the Holy See has always represented the final and inviolable obstacle in defense of human dignity against a globalist ideology," Cascioli wrote, according to Allen.

With the approach of the pope's encyclical, wrote Cascioli, "the Catholic Church is swept into the ecological chorus."

He maintains that environmentalists see overpopulation as the primary threat to sustainable development, according to Allen. For Cascioli, this means that the church will necessarily become wobbly on abortion and contraception.

"It's the usual story," Cascioli wrote. "To eliminate poverty, all you have to do is to physically eliminate the poor." He would not sacrifice "human life," he wrote, "even to save the planet."

Cascioli maintains that the environment can be cleaned up without engaging in population control, according to Allen.

"Cascioli's core point is that you can't buy only part of the secular environmental agenda. If Catholicism officially embraces the crusade against climate change, he warns, the momentum will carry the Church to places it will regret going," according to Allen.

Allen added that Cascioli speaks for "a powerful constituency in the Church, including Catholics most committed to pro-life causes."

Supporters of the forthcoming encyclical, such as author Christiana Peppard, see it as part of a continuing effort by the church to attune its teachings to scientific knowledge, according to The Daily Beast.

Crux is a subsidiary of The Boston Globe which is owned by businessman John Henry.

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