Pope Francis says that carbon pricing is "essential" to stem global warming — his clearest statement yet in support of penalising polluters — and appealed to climate change deniers to listen to science.

Key points: The Pope voiced his support for carbon pricing in an address to energy executives

The Pope voiced his support for carbon pricing in an address to energy executives He has been consistent in his calls for the world to move away from fossil fuels

He has been consistent in his calls for the world to move away from fossil fuels His 2015 papal encyclical, Laudato Si', called on stronger action on climate change

In an address to energy executives at the end of a two-day meeting, he also called for "open, transparent, science-based and standardised" reporting of climate risk and a "radical energy transition" away from carbon to save the planet.

Carbon pricing, via taxes or emissions trading schemes, is used by many governments to make energy consumers pay for the costs of using the fossil fuels that contribute to global warming, and to spur investment in low-carbon technology.

The Vatican did not release the names of those who attended the closed-door meeting at its Academy of Sciences, but a joint statement released after the meeting revealed ExxonMobil, BP, Royal Dutch Shell, Total, Chevron and Eni were in attendance.

It said that governments should set carbon pricing regimens at a level that encourages business and investment, while "minimising the costs to vulnerable communities and supporting economic growth".

The CEOs, as well as leaders of major asset managers such as BlackRock and BNP Paribas, also called for companies to provide investors with clarity about the risks climate change poses to their businesses and how they plan to transition to cleaner energy sources.

A small group of demonstrators gathered outside a Vatican gate.

One held a sign reading "Dear Oil CEOs — Think of Your Children".

Pope Francis, who has made many calls for environmental protection and has clashed over climate change with leaders such as US President Donald Trump, said the ecological crisis "threatens the very future of the human family".

'Doomsday predictions can no longer be met with irony'

California's long-running drought has exacerbated its annual fire seasons in recent years. ( AP: Mike Eliason/Santa Barbara County Fire Department )

He implicitly criticised those who, like Mr Trump, deny that climate change is mostly caused by human activity.

"For too long we have collectively failed to listen to the fruits of scientific analysis, and doomsday predictions can no longer be met with irony or disdain," he said.

The regions most at risk from climate hazards are Asia-Pacific and South Asia. ( Supplied )

He said discussion of climate change and energy transition must be rooted in "the best scientific research available today".

Last year, Mr Trump rejected projections in a report by his own government that climate change will cause severe economic harm to the US economy.

The US President also announced his intent to withdraw the country from the 2015 Paris deal to combat climate change, becoming the first country to do so among 200 signatories.

Francis's 2015 encyclical Laudato Si' — a significant document on Church teaching — called for greater protections of the environment, and strongly supported the Paris accord, and said time was running out to meet its goals.

"Faced with a climate emergency, we must take action accordingly, in order to avoid perpetrating a brutal act of injustice towards the poor and future generations," he said.

"We do not have the luxury of waiting for others to step forward, or of prioritising short-term economic benefits."

Oil companies have come under growing pressure from investors and activists to meet the Paris goals.

Companies including Royal Dutch Shell, BP and Total have laid out plans to expand their renewable energy business and reduce emissions, though many investors say they will have to do more.

AP/Reuters