Pope Francis is likely to have a major impact in spurring U.N. negotiations on global warming with an encyclical on the environment next week, the U.N.'s climate chief said today.

"Pope Francis is personally committed to this issue like no other pope before him," Christiana Figueres told a news conference.

The encyclical, a letter sent to bishops, due next Thursday would add a moral dimension to work on climate change for many believers, who would view it as a way to protect creation, she predicted.

"I do think the encyclical is going to have a major impact," Figueres, the head of the U.N. Climate Change Secretariat, said at the end of talks in Bonn, Germany, about a U.N. deal due to be agreed in Paris in December.

She said there was also a growing view among many governments, companies and investors that many actions to slow climate change would be economically profitable, rather than loss-making.

Combining moral and economic arguments could help a shift from fossil fuels towards renewable energies. "I believe that the transformation is on its way, it is irreversible and it is only going to pick up speed," she said.