"We have to adapt," he said. "The climate is changing. There's no doubt."
Brown's speech, at a Sacramento event organized by the Giannini Foundation of Agricultural Economics, touched on deforestation in Brazil and the melting of the Antarctic ice sheet.
He also discussed the challenge of pushing mass transit in California, where 38 million residents drive almost 1 billion miles per day.
"We can't do this overnight," he said.
Brown has repeatedly called attention to the dangers of climate change, including an increasing number of wildfires and the persistent drought.