Pope Francis warned Thursday that it would be "catastrophic" for world leaders to let special interest groups get in the way of a global agreement to curb fossil fuel emissions as he brought his environmental message to Africa on the eve of climate- change talks in Paris.

Francis issued the pointed warning in a speech to the U.N.'s regional office in Nairobi. He also spoke out against the illegal trafficking of blood diamonds, ivory and other natural resources.

Leaders from nearly 200 countries are set to meet on Nov. 30 to Dec. 11 in the French capital to formalize national pledges to cut carbon emissions and plans to transition to renewable energy. The meeting is meant to culminate in the signing of a global climate treaty that would phase out carbon emissions. The treaty is meant to establish actions each country will carry out in coming decades — including reducing carbon emissions from industry, energy and transportation sectors, and replacing fossil fuels with green energy including solar or wind.

Thursday was the second day in a row that Francis had touched on environmental concerns after he arrived in Kenya for a six-day pilgrimage. Before leaving for Uganda on Friday, he visited the Kangemi slum on Nairobi's northwestern edge and called for a "respectful urban integration" with concrete initiatives to provide good quality housing for all. He will return to Rome after a visit to the conflict-ridden Central African Republic.

Francis has made ecological concerns a hallmark of his nearly 3-year-old papacy, issuing a landmark encyclical earlier this year that paired the need to care for the environment with the need to care for humanity's most vulnerable.

He has accused the world's powerful countries of indulging a “selfish and boundless thirst” for money by ravaging the planet's natural resources and impoverishing the weak and disadvantaged in the process.

On Thursday, Francis repeated that message but took particular aim at those who reject the science behind global warming. In the United States, that includes some Republican presidential candidates and lawmakers, who have opposed steps President Barack Obama has taken on his own to cut greenhouse gas emissions.

"It would be sad, and dare I say even catastrophic, were special interests to prevail over the common good and lead to manipulating information in order to protect their own plans and interests," Francis said.

Francis, who has said global warming is "mainly" man-made, said the world was faced with a stark choice: either improve or destroy the environment. He said he hoped the Paris talks, which begin on Monday, would approve a "transformational" agreement to fight poverty and protect the environment by developing a new energy system that depends on minimal fossil fuel use.

"Many are the faces, the stories and the evident effects on the lives of thousands of people for whom the culture of deterioration and waste has allowed to be sacrificed before the idols of profits and consumption," he said. "We cannot remain indifferent in the face of this. We have no right."

He noted that some scientists consider protection of the Congo basin tropical forest, which spreads over six countries and is the world's second-largest after the Amazon, essential for the future of the planet because of its biodiversity.

Francis also spoke out against the illegal trafficking of blood diamonds, ivory and other natural resources, saying the trade fueled political instability and organized crime.

"We cannot be silent about forms of illegal trafficking which arise in situations of poverty," he said.

Figures published earlier this year by Amnesty International showed conflict diamonds, which account for four percent of total global production, have helped finance civil wars and prop up military regimes.

The pontiff's remarks on wildlife trafficking were likely to hit home in Kenya, a country trying to stamp out rampant poaching to protect its remaining elephant population.

Hundreds of elephants are lost to poaching every year, with conservationists warning the African elephant could be extinct in the wild within a generation.

Al Jazeera with wire services