At a two-day conference at the Vatican, the pope called climate change a challenge of “epochal proportions,” according to Reuters.

He also said that the world must move toward using clean energy and a reduction in the use of fossil fuels.

“Civilization requires energy but energy use must not destroy civilization,” Francis said.

The conference, organized by the University of Notre Dame in the United States, brought together executives from asset manager BlackRock, BP and Norwegian oil and energy company Equinor, among others.

The event was prompted by Francis’s 2015 papal encyclical blaming humans for climate change and criticizing world leaders for not acting swiftly enough to address it.

The conference comes a little less than a year after President Trumppulled the U.S. out of the Paris climate accord. Trump has referred to global warming as a “hoax” and drawn criticism from the scientific community for stacking his administration with officials who deny the human role in climate change. During a meeting with Trump, the pope gave him a copy of the encyclical.

The pope told the group Saturday that global issues like poverty are “interconnected” to concerns about global warming and access to electricity.

“We know that the challenges facing us are interconnected,” he said, according to Reuters. “If we are to eliminate poverty and hunger ... the more than one billion people without electricity today need to gain access to it.”

“But that energy should also be clean, by a reduction in the systematic use of fossil fuels,” he added. “Our desire to ensure energy for all must not lead to the undesired effect of a spiral of extreme climate changes due to a catastrophic rise in global temperatures, harsher environments and increased levels of poverty.”