Pope Francis has called for urgent political and spiritual conversion of global leaders and individuals in curbing climate change and ending policies that destroy the environment.

In a radically worded letter that was published on Thursday, the leader of the world's 1.2 billion Catholics blamed human greed for the critical situation "Our Sister, mother Earth" now finds itself in.

Under threat from climate change

"This sister now cries out to us because of the harm we have inflicted on her by our irresponsible use and abuse of the goods with which God has endowed her," Francis writes.

Arguing that environmental damage is intimately linked to global inequality, he said doomsday predictions can no longer be dismissed, and "the earth, our home, is beginning to look more and more like an immense pile of filth".

Green activists hailed the Pope's widely-trailed intervention as a potential game-changer in the debate over what causes global warming and how to reverse it.

"Everyone, whether religious or secular, can and must respond to this clarion call for bold urgent action," said Kumi Naido, the international executive director of Greenpeace.

Environmentalists hope the Pope's message will significantly increase the pressure for binding restrictions on carbon emissions to be agreed at global talks in Paris at the end of this year.

Earlier this year, Francis also addressed the issue of the environment during his visit to the Philippines, which was hit by the supertyphoon Haiyan.

Criticism

But even before the official publication, following a leak of the letter, climate change sceptics had dismissed the document's argument that the phenomenon is primarily man-made and that humanity can reverse it through lifestyle changes including an early phasing-out of fossil fuels.

Pope Francis puts US Republicans in a corner on climate change

"I don't get economic policy from my bishops or my cardinal or my pope," US presidential candidate, Jeb Bush, who is a Catholic convert, said on the eve of the release in comments that underlined the depth of opposition in the United States to a binding agreement to curb greenhouse gases.

The letter references the arguments of the sceptics by acknowledging that volcanic activity, variation in the earth's movements and the solar cycle are factors in climate change.

But it maintains that "most global warming in recent decades is due to the great concentration of greenhouse gases released mainly as a result of human activity".

And it leaves no doubt that Francis believes the world is on a fast-track to disaster after decades of inaction.

"If present trends continue, this century may well witness extraordinary climate change and an unprecedented destruction of ecosystems, with serious consequences for all of us," he writes.

Bemoaning the "remarkable" weakness of political responses to this, Francis accuses the sceptics of cynically ignoring or manipulating the scientific evidence.

"There are too many special interests, and economic interests easily end up trumping the common good and manipulating information so that their own plans will not be affected," he writes.