Pope Francis says the world urgently needs a "bold cultural revolution" to tackle the looming challenge of catastrophic climate change while addressing the needs of the poor.

In a much-anticipated, 184-page encyclical, the reformist Pope endorsed the scientific consensus that humankind is causing a dramatic shift in the world's climate, which will have the greatest impact on the world's poor. But he rejected the notion that market mechanisms or technological approaches alone can provide the solution.

While those tactics may be useful, the more fundamental answer requires society to redefine our notion of progress and re-evaluate our relationship with God, the Earth and one another, Pope Francis wrote in Laudato Si, which in Latin means Praise Be.

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"Today, we have to realize that a true ecological approach always becomes a so­cial approach; it must integrate questions of jus­tice in debates on the environment, so as to hear both the cry of the earth and the cry of the poor," he wrote.

The popular 78-year-old pontiff is an Argentine Jesuit who has angered some Roman Catholics with his emphasis on the poor and his tolerance of gays. He took the title of his encyclical from a poem by his namesake, St. Francis of Assisi, who was known for his humility and his love of the natural world.

The pope's encyclical is a formal teaching document that does not bind the Roman Catholic faithful, but establishes a moral argument for taking action on climate change. In it, he lays out the theological underpinnings for his call: that humankind is meant to live in harmony with God, with our neighbour and with the Earth itself. That harmony has been broken in the world, and that rupture is sin.

"The pace of consumption, waste and envi­ronmental change has so stretched the planet's capacity that our contemporary lifestyle, unsus­tainable as it is, can only precipitate catastrophes," he wrote.

Conservative critics have long argued that environmentalists – and the United Nations' Intergovernmental Panel on Climate Change (IPCC) – have been alarmist in their warnings about impending catastrophe and rely on unverifiable modelling. Energy executives from the coal and oil industries suggest aggressive action on climate change would hurt the world's poor who need access to low-cost fossil fuels.

Prime Minister Stephen Harper has faced considerable criticism for his perceived role in opposing aggressive action. There were reports that Canada insisted on watering down a Group of Seven statement earlier this month that ended up calling for "deep decarbonization" by the end of this century.

It's hard to say how much impact the Pope's statement will have. But it comes just six months before world governments gather in Paris to conclude a global climate agreement, and three months before he travels to the United States, where the debate over climate change is particularly polarized and where he will address Congress.

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In the U.S. Republican party, social conservatives who represent the base of the party have held similar positions to the Catholic Church on the right to die, abortion and same-sex marriage. Climate change will test that trend. Earlier this week, leaked excerpts of the encyclical were roundly criticized. Several Republican presidential candidates either question the science behind climate change or suggest the threat is exaggerated – they also happen to be Roman Catholic.

In the House of Commons Thursday, Green Party Leader Elizabeth May urged the Harper government to show the same level of urgency in its approach to climate change as Pope Francis has shown. Environment Minister Leona Aglukkaq said Canada is doing its part by, for example, phasing out traditional coal-fired power in Canada and supporting renewable energy projects overseas.

The encyclical "is an astonishingly thoughtful and important document," Ms. May said in an interview. "It is clearly intended to create greater momentum for the Paris talks; it's highly critical of the procrastination over the decades and I do believe it will make a difference."

With a report from Affan Chowdhry