The Pope is expected to use his first address to the United Nations to deliver a powerful warning over climate change in a move to adopt protection of the environment as a "moral" cause for the Catholic Church and its billion-strong following.
The New York speech is likely to contain an appeal for sustainable development, and it will follow an unprecedented Encyclical (a message to the wider church) on the subject, senior diplomatic sources said.
It will act as the centrepiece of a US visit scheduled for next April – the first by Benedict XVI, and the first Papal visit since 1999 – and round off an environmental blitz at the Vatican, in which the Pope has personally led moves to emphasise green issues based on the belief that climate change is affecting the poorest people on the planet, and the principle that believers have a duty to "protect creation".
Cardinal Cormac Murphy-O'Connor, head of the Catholic Church in the UK, said last night: "This is a crucial issue both today and for all future generations. We are the stewards of creation and we need to take that responsibility seriously and co-operate to care for the created world."
A Papal tour of America will be particularly potent during election year in the US, where Catholics number around 73 million, and is being discussed in Rome after Pope Benedict accepted an invitation from the UN secretary general, Ban Ki-moon. For the Pope to take his climate-change message to the high-profile UN platform will be considered hugely influential to the fifth of the world's population who are Catholics, and will act as a rallying call for action in Africa and Asia, which have seen a rise in Catholics in recent years.
News of the speech comes as Vatican City has become the first fully carbon-neutral state in the world, after announcing it is offsetting its carbon footprint by planting a forest in Hungary and installing solar panels on the roof of St Peter's Basilica in Rome.
It also follows a series of interventions by the Pope on the environment. On 2 September he told a 300,000 youth audience: "Before it is too late, it is necessary to make courageous decisions that reflect knowing how to re-create a strong alliance between man and the earth." On 7 September, he said there was a "pressing need for science and religion to work together to safeguard the gifts of nature and to promote responsible stewardship".
UK diplomats have held a number of behind-the-scenes meetings with Vatican officials on the environment. A Whitehall source said last night: "Benedict is the spiritual head of 19 per cent of the world's population and a highly respected figure. If the Pope's words are taken on board by his community that is one big constituency for change and could well turn the tide on climate change and environmental degradation."