The Pope's closest adviser on ecology has urged Catholics to join global climate marches planned for Sunday.
In an internal letter to bishops, Cardinal Peter Turkson says people should be "encouraged" to exercise their "ecological citizenship".
The letter says that climate negotiators meeting in Paris need to hear the voice of "God's people".
Activists say the call is evidence of a step-change in the Church's approach to climate change.
Major demonstrations across the world have been planned to mark the start of the global climate conference, known as COP21.
In Paris, planned big rallies have been cancelled in the wake of the 13 November attacks which killed 130 people.
Nearly 1,000 people thought to represent a security risk have been barred from entering the country, said Interior Minister Bernard Cazeneuve.
A handful of other activists have been placed under house arrest under emergency powers introduced following the attacks.
But elsewhere protesters have taken to the streets to demand action.
'Offer your support'
Over the next two weeks, delegates meeting here are hoping to strike a new, far-reaching deal on climate change.
In his letter to around 5,000 Catholic bishops around the world, the cardinal makes it clear that relying on political leaders to achieve environmental justice is not enough.
He states that more than one million people around the world are likely to take part in climate marches on 29 November.
The marchers will be exercising "global ecological citizenship", he says, and he suggests to the bishops that they "are warmly invited to offer your support in prayer, word and action".
The letter gives contact details for the bishops on how to find out about marches in their diocese.
"If you could please encourage the faithful and many others to exercise their 'ecological citizenship', this would surely help to reinforce the humble and peaceable spirit of Laudato si', and it would spiritually express communion with the universal church," the letter reads.
Cardinal Peter Turkson is president of the Pontifical Council for Justice and Peace but is seen as the Pope's point man on climate change.
A sometimes controversial figure within the Church, he was touted as a potential replacement after Pope Benedict's retirement.
Under Pope Francis he has emerged as a leading advocate for the environment and helped write the first draft of the Pope's landmark encyclical, Laudato Si'.
The Pope has expressed his worries that the negotiating process here in Paris may fail to deliver a global agreement. He said it would be "catastrophic" if global leaders let special interest groups derail the deal.
Speaking in Nairobi earlier this week, the Pope said the world faced a stark choice to either "improve or destroy the environment".
Environmental campaigners are in little doubt that the letter to Catholic bishops is in keeping with the Pope's progressive stand on climate change.
"In the letter he is not only asking people to go to the streets, he is asking them to pray as well," said Oscar Soria from Avaaz, who are organising the global marches.
"I think it is a continuation of the Pope's narrative right now, from the encyclical, to his speech at the United Nations, then to Nairobi and then the climate march.
"It's clear sign that the Vatican is stepping up its climate battle in a way never seen before."
In Paris, an installation of "marching shoes" will be built with contributions from thousands of people. The Pope has agreed that a pair of shoes bearing his name will be part of the display.
Cardinal Turkson is expected to attend COP21 as part of the official Holy See delegation.
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