Hillary Clinton must be "cautious and wise" moving forward as she remains in many quarters the Democratic front-runner for president in 2016, warned Calif. Gov. Jerry Brown.

Brown told ABC's George Stephanopoulos on "This Week" that there are risks associated with leading the pack at this point before the next presidential election.

"I would say she's the overwhelming favorite," he said. "I can't see any opposition or even potential opposition. Whether it's a good thing or not, it does carry with it risk."

Brown is a veteran of the presidential campaign process, having run against former President Bill Clinton for the nomination in 1992.

"Being a front-runner is being on a perch that everyone else is going try to knock you off of, he said. "She's there, she's got the capacity, but like any front-runner, she has to be cautious and wise in how she proceeds forward."

Brown appeared on ABC today after a series of fires ripped through Southern California this week, forcing tens of thousands of people to evacuate, charring huge swaths of land and causing close to $20 million in damage. Brown said the fires were relatively under control, but used the interview on "This Week" to take aim at Republicans who deny climate change and layout what he sees as a broader climate challenge.

"It is true that there's virtually no Republican who accepts the science that virtually is unanimous," said Brown. "I mean there is no scientific question. There's just political denial for various reasons, best known to those people who are in denial."

"We're going to deal with nature as best we can, but humanity is on a collision course with nature and we're just going to have to adapt to it in the best way we can," he added later.