Gov. Jerry Brown, speaking Tuesday at a conference hosted by Pope Francis, accused climate change skeptics of trying to "bamboozle" local leaders trying to cut emissions and said he had no faith that Congress would act on global warming.
"It's up to you guys," the governor told more than 60 mayors from around the world who were invited to the climate conference at the Vatican.
The governor reprised a message he has delivered in Sacramento and elsewhere, including a recent Toronto conference on the environment: Climate change skeptics are "troglodytes."
The former Jesuit seminarian threw his weight behind Francis' recent encyclical, Laudato Si, a powerful document in which the pope spells out his belief that creeping climate change is contributing to global poverty.
In an address to the conference later in the day, the pope urged the United Nations to step up its campaign to moderate the effects of climate change.
"I have great hopes for the Paris summit in December and hope a fundamental agreement is reached," Francis said, referring to a key meeting at which a U.N. climate deal should be signed.
Francis urged mayors to speak up, warning that "if the message does not come from the ground up, it will not have any effect."
For their part, Brown and the other local leaders signed a declaration stating that "human-induced climate change is a scientific reality, and its effective control is a moral imperative for humanity."
The Paris conference, the declaration added, "could be the last effective opportunity" to limit the rise in Earth's temperature to 2 degrees Celsius.
The Vatican gathering, which also addressed human trafficking, drew mayors from 10 U.S. cities, including New York, San Francisco and San Jose, as well as from Madrid, Buenos Aires and Paris.
Los Angeles Mayor Eric Garcetti did not attend, and spent part of the day speaking to the county Board of Supervisors urging an increase in Los Angeles County's minimum wage, a signature issue for him.
Garcetti and Mayor Annise Parker of Houston, who helped launch the Mayors National Climate Change Agenda, put out a statement endorsing the declaration issued at the Vatican and calling on world leaders "to think like mayors and share our sense of urgency."
New York Mayor Bill de Blasio, speaking after Brown, thanked the California governor for being "the leading voice in the nation" on climate change, and announced his intention to cut greenhouse gas emissions in New York City by 40% by 2030, following California's example.
Speakers highlighted the role mayors can play fighting climate change, given that half the world's population now lives in cities, which are responsible for nearly three-quarters of the planet's greenhouse gas emissions.
Brown gave a glowing review of his own achievements in cutting emissions in California, offering it as a template for mayors around the world.
California derives 25% of its energy from renewable sources and has the most efficient buildings in the United States, as well as 40% of the country's electric cars, he said.
"But we are not stopping there," Brown said, adding that he wanted renewable energy to reach 50% and gasoline use in cars and trucks to drop by 50% in 15 years.
Backing up his call to action, the governor quoted St. Paul on man reaping what he sows. He also cited Italian communist leader Antonio Gramsci, who described the "pessimism of the intellect, optimism of the will."
Brown called for a campaign against the "fierce opposition and blind inertia" of "well-financed" climate change skeptics.
With national leaders proving unwilling to act, the governor called on mayors "to light a fire, if I may use that metaphor — in terms of climate change, it's probably the wrong one."
"We have very powerful opposition that, in at least my country, spends billions on trying to keep from office people such as yourselves and elect troglodytes and other deniers of the obvious science," Brown said.
In his speech, New Orleans Mayor Mitch Landrieu described Hurricane Katrina, which tore across depleted wetlands, as lifting "a veil" that revealed the "ugly, scary, reality" of environmental destruction in the U.S., adding that the subsequent BP oil spill was the climax of 100 years in which the Louisiana coast was "slashed and burned for the benefit of the American oil consumer."
Edwin Lee, the mayor of San Francisco, said mayors had vital hands-on experience of "ensuring sustainable infrastructure." He said he would switch all city vehicles in San Francisco to renewable fuel — made from natural fats, oils and greases — by the end of the year, reducing greenhouse emissions in the fleet by 60%.
Brown stayed at the Rome residence of the U.S. ambassador to Italy and met with Father Adolfo Nicolas, superior general of the Jesuits. As a young man, Brown was drawn to the priesthood, but left seminary for a secular education and his eventual career in politics.
In an interview on the eve of the conference, the governor said he backed Francis' view of nature as part of God's creation, to be safeguarded as carefully as humanity itself.
"He talks about the 'web of life' and sums up the encyclical as stating everything in nature is an expression of the divine and therefore we have to take it seriously," Brown said.
Brown said he hoped other religious leaders would follow the pope's lead.
"The pope is dealing with the biggest threat of our time," he said. "If you discount nuclear annihilation, this is the next one. If we don't annihilate ourselves with nuclear bombs, then it's climate change. It's a big deal and he's on it."