Gov. Gavin Newsom accused former President Trump of “open corruption” in a speech Thursday at a climate summit of Catholic officials and international leaders, elevating his criticism of the Republican leader in the hallowed halls of the Vatican.

The California governor referenced news stories alleging that Trump recently solicited campaign donations from oil executives and at the same event vowed to walk back climate protections if elected in the 2024 presidential contest.

“He openly asked them for $1 billion to roll back the environmental progress of the Biden administration, environmental progress that we’ve made over the course of the last half century,” Newsom said. “Open corruption. A billion dollars to pollute our states, to pollute our country, and to pollute this planet and roll back progress.”

The governor spoke at a three-day “From Climate Crisis to Climate Resilience” summit organized by the Pontifical Academy of Sciences.

Newsom said he decided to call out Trump by name at the international gathering of governors, mayors and policy experts because he felt stories about Trump’s meeting with oil executives didn’t get enough attention.

“It’s an expression of my sincerity about how serious I take this moment and how consequential it is,” the governor said about the possible negative effects on climate change if Trump returns to the White House.

His comments were also strategic. Climate change isn’t necessarily driving American Catholics to the polls, but drawing attention to an accusation of pay-to-play political corruption might resonate more with Pope Francis’ supporters in the U.S. More than 50 million Americans identify as Catholic.

Newsom’s appearance is likely to elevate his position as a climate leader on a world stage.

With temperatures and carbon emissions rising worldwide, the aim of the conference is for local and state governments to share best practices about fighting climate change and adapting to hotter temperatures, rising seas and a more volatile environment.

Parts of Newsom’s talk matched the tenor of a critique of the oil industry he delivered last fall at the United Nations Climate Ambition Summit in New York.

“It’s because of the burning of gas, the burning of coal, the burning of oil,” Newsom said at the Vatican. “We have the tools. We have the technology. We have the capacity to address the issue at a global scale and they’ve been fighting every single advancement and we have got to call that out.”

Bob Salladay, Newsom’s top communications advisor, said his candid assessment earlier in New York of the industry, which he said was playing everyone for fools, caught the attention of the Vatican and is one of the reasons he was invited to speak at the climate summit.

The setting of his speech, in a carpeted auditorium at the Vatican that typically houses gatherings of bishops, drew a stark contrast to the marbled floors and renaissance murals that lined the walls and ceilings of Clementine Hall, where Newsom spoke with Pope Francis on Thursday morning.

In an address to government leaders and climate scientists in Clementine Hall, Pope Francis cast the destruction of the environment as an offense against God.

“This is the question: Are we working for a culture of life or for a culture of death?” Pope Francis said.

Newsom and his wife, First Partner Jennifer Siebel Newsom, sat in the second row of the audience in an Apostolic Palace near St. Peter’s Basilica.

A pope’s body is placed in the hall for private visitation upon his death. It’s also the same room that former President Obama visited in 2009.

New York Gov. Kathy Hochul greets Pope Francis on Thursday in Vatican City.

(Riccardo De Luca / Associated Press)

Pope Francis called the refusal to protect the most vulnerable who are exposed to climate change caused by human activity a “grave violation of human rights.”

He said around 1 billion people in wealthier nations “produce more than half the heat trapping pollutants” of the world. Poorer people, he said, contribute less than 10% and suffer 75% of the resulting damage.

Pope Francis also took a shot at fossil fuel companies.

“An orderly progress is being held back by the greedy pursuit of short-term gains by polluting industries and by the spread of disinformation, which generates confusion and obstructs collective efforts for a change in course,” Francis said.

The governor called the pope’s address “remarkable.”

“I knew what I was going to say already, but he said it before I said it,” Newsom said.

After Francis’ speech, Newsom and Siebel Newsom walked along an aisle of ornate stone tiles to the front of the room, where the governor briefly spoke with the leader of the Catholic Church. The governor said the pope commended his administration’s work on the death penalty.

The governor said he was struck by the pope’s support for what Newsom described as a difficult decision to issue a moratorium on the death penalty and close California’s execution chambers in 2019.

At the time, more than 700 people were on death row. Newsom met with families of some of the victims who had been killed by the inmates.

“It was nice that he brought up the issue and thanked California for the direction we’re going,” Newsom said.

Newsom’s action ran counter to the expressed will of California voters, who over the previous six years had rejected two statewide ballot measures to repeal the death penalty.

A procession of attendees also greeted the pope, who took time to shake hands with every person in the room.

The pope signed a planetary compact after his speech, which Newsom and other government leaders also signed Thursday.

Wade Crowfoot, California’s Natural Resources secretary, described the compact as an unprecedented agreement among international governors, mayors, Indigenous leaders and scientists to work together to confront climate change with a focus on resiliency and equity.

Crowfoot and Lauren Sanchez, Newsom’s top climate advisor, also participated in hours of meetings at the conference on Wednesday.

Newsom is hosting a state climate summit in Southern California this fall as a continuation of the work at the Vatican conference. The state will be inviting local leaders and experts from California.

“We’re taking the torch of subnational leadership back to California, where it belongs, to convene scientists, local governments and leaders to tackle the climate threat that is the existential crisis of our time,” Sanchez said.

Some environmentalists in California said Newsom’s rhetoric on the global stage is not entirely matched by his actions at home. Though Newsom has championed many environmental measures and has waged a battle with oil companies as governor, he proposed cutting $3.6 billion for climate-related programs to help address the state budget deficit.

Susan Stephenson, executive director of a religious environmental advocacy organization called Interfaith Power and Light, took issue with a recent decision by Newsom’s appointees on the California Public Utilities Commission that she said would slow the use of rooftop solar power.

“He’s saying a lot of the right things,” Stephenson said. “And it is not matched by the urgency of action that we need as climate change is worsening.”

Newsom has also received criticism from some Republicans for traveling abroad instead of staying home to focus exclusively on California’s problems.

That was not the sentiment of a Democratic couple from Riverside who saw Newsom and his wife on a tour of the Roman Forum after the speech. They said they were surprised to see the governor in Rome.

Walter and Susan Davis said they believe in climate change and support the governor coming to deliver the speech, which they called “a real reason.”

“That’s what I’m talking about,” Walter Davis said.

Times Sacramento Bureau Chief Laurel Rosenhall contributed to this report.