Pope Francis on Thursday warned of a "catastrophic" outcome if vested interests blocked an agreement to tackle climate change at the UN talks opening in Paris next week.

"In a few days, an important meeting on climate change will be held in Paris... It would be sad, and I dare say even catastrophic, were particular interests to prevail over the common good and lead to manipulating information in order to protect their own plans and projects," he said ahead of the summit which officially starts on Monday.

"We are confronted with a choice which cannot be ignored: either to improve or to destroy the environment," he said in a speech at the world headquarters of the UN Environment Programme (UNEP) in the Kenyan capital Nairobi.

Although he did not go into further detail, the pope has pointed the finger at big industry and blamed first-world countries for failing to act to curb global warming.

Francis, who is on his first visit to Africa, arrived in Kenya late on Wednesday with a warning that the world was facing "a grave environmental crisis" as he began a landmark three-nation tour which will also take him to Uganda and the Central African Republic.

The 78-year-old pontiff has taken on a vocal role in the fight against climate change, injecting a moral voice into a debate usually dominated by scientific, economic and political concerns.

His comments were made just four days before the start of COP21, a 12-day conference in the French capital which aims to secure a climate rescue pact.

More than 150 heads of state and government are due to attend the start of the conference, which is due to wrap up on December 11.

Negotiators are to start talks on Sunday, a day ahead of schedule.

"COP21 represents an important stage in the process of developing a new energy system which depends on a minimal use of fossil fuels, aims at energy efficiency and makes use of energy sources with little or no carbon content," the Argentine pope said, stressing the need to rethink global models of economic development.

- Hope for a deal -

"The Paris agreement can give a clear signal in this direction," said Francis who has drawn a "clear link" between climate concerns and social justice.

"For this reason, I express my hope that COP21 will achieve a global and 'transformational' agreement based on the principles of solidarity, justice, equality and participation; an agreement which targets three complex and interdependent goals: lessening the impact of climate change, fighting poverty and ensuring respect for human dignity."

The leader of the world's 1.2 billion Catholics took a firm stance on environmental issues earlier this year, issuing a lengthy 'encyclical' which said climate change was primarily man-made and one of the main challenges facing humanity.

It also denounced inequality, saying poor countries that are least to blame for rising seas, increasing drought and flooding were likely to be worst hit by the changes and needed the help of rich economies.

Prince Charles warns of 'perfect storm' should Paris climate talks flop
Valletta (AFP) Nov 26, 2015 - Prince Charles warned Thursday that if international leaders fail to clinch a deal on climate change at talks in Paris next week, it would leave mankind facing a "perfect storm".

"This meeting falls at a very important, indeed critical moment for the future of mankind and our planet," he said in a speech at the Commonwealth summit in Malta.

"Countless concerned people around the world" are banking on global leaders to come up with an ambitious long-term goal for the rapid reduction of carbon emissions, he said, as Commonwealth leaders began to arrive on the rain-lashed Mediterranean island.

"We face an unprecedented set of interlocking challenges, all of which are creeping up on us in the shape of perfect storm," he added, from unsustainable population growth to migration, rapid globalisation, and social economic and energy insecurity.

The Commonwealth family of 53 nations is gathering in Malta for three days of talks from Friday with a focus on reaching agreements that will open doors for wider deals at the COP21 climate talks in Paris, which begin on Monday.

Queen Elizabeth II, the head of the Commonwealth, is making a state visit to Malta to coincide with the summit, supported by her husband Prince Philip, their eldest son Charles and his wife Camilla.

- 'Tensions' -

The Commonwealth Heads of Government Meeting sees countries including Britain, Canada, India and South Africa sit down on equal terms with tiny Caribbean island nations and developing microstates.

"The beauty of the Commonwealth is that its diversity makes it into a prototype or microcosm of the whole world," its Secretary-General Kamalesh Sharma said.

Born out of the British empire, the Commonwealth of Nations brings together around a quarter of the world's countries and a third of its population.

"The Commonwealth reflects the tensions that exist because around the same table you have some of the most developed and vulnerable economies in the world," said Maltese Prime Minister Joseph Muscat, who is hosting the summit.

"Most other groupings either have a region or an economic standing in common."

Muscat said he was targeting strong outcomes rooted in "realism" as the organisation tackles issues of "direct concern" -- namely climate change, extremism, trade and migration issues.

On climate change, Sharma said the summit's final statement should have a "strong political component" and would also "indicate measures which the Commonwealth is going to undertake, particularly for small and vulnerable states".

"It's a larger question of moral hazard and of an ethical imperative," he explained.

"Small states that have contributed most negligibly to the carbon footprint of the world would be the first to be affected" by the consequences of global warming.

"We will come up with ideas of how to build capacities and access finance."

- 'Trillions of dollars' -

Prince Charles said the influence of the Commonwealth should not be underestimated, but he insisted deals made here would mean little if the private sector could not be persuaded to get behind the climate change fight and provide financial aid.

"If there is one thing other than taxes and death of which we can be certain, it is that there is never going to be enough public money to implement the SDGs (Sustainable Development Goals) or Paris agreement," he said.

"Billions of dollars will need to become trillions of dollars," he insisted, with an "estimated 90 trillion dollars needed for infrastructure development alone over the next 15 years, in order to have any hope of keeping us in a world only 2.0 degrees warmer".

World leaders including French President Francois Hollande and UN Secretary General Ban Ki-Moon were expected to join the climate debate talks in Valletta on Friday, fine-tuning details before the UN summit kick-off Monday.

The outcome of the Paris talks would "determine the survival of our species and all those who share this precious planet with us," Charles said.

"We do not have the right to test to destruction the planet's tolerance to our indiscretions. We do have a responsibility to act now," he said.