Mr. Clinton spoke for half an hour to about 1,500 supporters and students at the University of South Carolina Upstate in Spartanburg. Hundreds of volunteers, supporters and curiosity seekers packed into the school's gymnasium several hours before the former president took the stage, leading chants and cheers on top of rock 'n roll tunes.
"Fighting climate change is the greatest challenge this country has had since we mobilized for World War II," Mr. Clinton said. "If we replaced every incandescent light bulb in this country ... it would have the same effect as taking 70,000 cars off the road."
Hillary Clinton "has continued to work around the world on climate change and other issues," he said. "We don't have any margin for error. We need to get this show on the road and get America back in business again."
Mr. Clinton, who said he and his wife recently celebrated their 32nd anniversary, said he'd gladly support the New York senator's presidential bid even if the two were not married.
"I'd be here for her, and it'd have nothing to do with the fact that we've spent the last 32 years together," he said. "It's not that I dislike the other candidates. ... If you want me to say something bad about them, you can leave now."
The New York senator's expertise on military issues will also serve America well in the White House, Mr. Clinton said.
"Hillary's the only member of the Armed Services Committee running for president," Mr. Clinton said. "We cannot continue to string up deployments that are longer today then they were in World War II."
Mr. Clinton also expressed his condolences to Clemson University and the University of South Carolina for the loss of seven students in a North Carolina beach house fire over the weekend.
"We just want all the people of South Carolina to know that our hearts are with you, with this terrible, terrible fire that cost the lives of students," Mr. Clinton said. "Those things happen, but it doesn't make it any easier, and we're thinking about you."
In welcoming Mr. Clinton to his hometown of Spartanburg, former Democratic National Committee Chairman Don Fowler praised the former president.
"He's a magician. He understands. He cares. He leads," Fowler said, to loud applause. "This is the man who did it, and his wife is going to do it again."
One supporter filing into the gymnasium to get a seat in the standing-room only crowd said she wasn't sure whom to support for president.
"I haven't made up my mind entirely so I'm here to see Bill. I love him dearly," said Barbara Baco, of Spartanburg. "If they'd change the Constitution so he could run again, I would vote for him, most certainly."
The former president planned to speak later Monday at The Freedom Center, a mostly black non-denominational church in Rock Hill, campaign spokesman Zac Wright said.