By Philip Pullella

VATICAN CITY (Reuters) - The world could see the destruction of entire ecosystems this century without urgent action on climate change, Pope Francis says in a draft of his keenly awaited encyclical on the environment.

In the Italian version of the 192-page document, posted on Monday by the weekly magazine l'Espresso, the pope again backs scientists who say global warming is mostly man-made and that developed countries have a particular responsibility to stem a trend that will hurt the poor the most.

That position has been contested by conservatives, particularly in the United States, who have excoriated the first pontiff from Latin America for deploying scientific arguments.

The Vatican condemned the leak but did not deny the document's authenticity. It later informed veteran journalist Sandro Magister that his media credentials within the Holy See were being suspended indefinitely because the leak had caused "great turmoil".

A spokesman said the final version would remain under embargo until its scheduled release on Thursday.

Still, Italy's major newspapers published pages of excerpts in their Tuesday editions.

"If the current trend continues, this century could see unheard-of climate change and an unprecedented destruction of ecosystems, with grave consequences for all of us," Francis writes, according to the leaked version.

By making environmental protection a moral imperative, Francis' intervention could spur the world's 1.2 billion Catholics to lobby policymakers on ecology issues.

The pope has said he wants the document, called "Laudato Si (Be Praised), On the Care of Our Common Home", to be part of the debate at a major U.N. summit on climate change this year in Paris. He said on Sunday the document was addressed to all people, regardless of religion.

Meanwhile, Justin Welby, the Archbishop of Canterbury and spiritual head of the world's 80 million Anglicans, issued a declaration on Tuesday along with representatives from Britain's Catholic, Muslim, Sikh and Jewish communities among others, calling for urgent action to tackle climate change.

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"We are faced with a huge challenge. But we are hopeful that the necessary changes can be made – for the sake of all who share this world today - and those who will share it tomorrow," their joint declaration said.

According to the leaked excerpts from the pope's six-chapter document, destined to become a signature document of his papacy, Francis speaks of "symptoms of a breaking point caused by the great speed of change and degradation".

It was not clear how advanced in the writing process the leaked document was nor how similar it would be to the final version. The leaked document bore the pope's signature in Latin.

"IMMENSE GARBAGE DUMP"

It confirmed what people familiar with the final version told Reuters last week about how the document addresses climate change and the man-made causes of global warming.

"The Earth, our home, increasingly seems to be transforming itself into an immense garbage dump," the pope writes.

He confronts climate change deniers head-on, saying there is a "very consistent scientific consensus that we are experiencing a worrying warming of the climactic system".

While acknowledging there are other factors, he says numerous studies have shown that global warming is caused by greenhouse gases emitted mainly because of human activities.

The encyclical urges rich nations to re-examine their "throw-away" lifestyle, an appeal Francis has made often since his election in 2013.

"Enormous consumption in some rich countries has repercussions in some of the poorest places on Earth," he says, according to the leaked draft.

The pope calls for a reduction in carbon emissions, an increase in policies that favor renewable energy and warns of the long-term effects of continuing to use fossil fuels as the main source of global energy.

He also rejects suggestions that population control would solve the environmental crisis, saying one of the main causes is "extreme consumerism".

(Editing by Louise Ireland)