During a climate summit in Vatican City, Calif., Gov. Jerry Brown insinuated Tuesday that climate change could lead to "extinction."
"We don't even know how far we've gone, or if we've gone over the edge," said Brown, a Democrat. "There are tipping points, feedback loops, this is not some linear set of problems that we can predict. We have to take measures against an uncertain future which may well be something no one ever wants.
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"We are talking about extinction. We are talking about climate regimes that have not been seen for tens of millions of years. We're not there yet, but we're on our way. And there's an element of irreversibility that requires that we imagine, down the road in the future, and then react."
Brown spoke to
dozens of mayors and local officials from across the world in the Synod Hall in the Vatican. He criticized what he called "fierce opposition and blind inertia" in the U.S. by people skeptical of global warming, who he says are trying to "falsify the scientific record" as they try convince people global warming is not actually happening.
Pope Francis was expected to address the officials later on Tuesday at the two-day summit.
Those in attendance are expected to
sign a Vatican declaration urging world leaders to take bold action at Paris climate talks this December.
The Vatican has gotten involved in the climate change debate in recent months. Pope Francis
released a 190-page encyclical last month, in which he discussed climate change.
The Pope argued "a very solid scientific consensus" indicates that global warming is real, and will limit drinking water, harm agriculture, lead to extinctions of plant and animal life, acidify oceans and raise sea levels.
Pope Francis also urges humans to make some lifestyle changes, such as "using public transport or car-pooling, planting trees, (and) turning off unnecessary lights."
The Pope added that while some climate change occurs naturally, studies indicate it "mainly" stems from human activity.
French President Francois Hollande
addressed climate change during a speech in Paris on Tuesday, calling for nations to submit their emissions reduction targets before the Paris summit later this year.