That high-profile statement, political analysts say, may have marked a major turnabout for the president, who has scarcely mentioned global warming – or the more scientific designation of "climate change" – in recent months.
Ever since an attempt to pass cap-and-trade legislation to limit greenhouse gas emissions failed in 2010, the president has seemed almost mute on the topic – with a few rare exceptions mostly when speaking overseas, frustrated environmentalists say.
"Two years ago the White House communications shop decided this was not a good issue to talk about," says Joe Romm, a senior fellow at the Center for American Progress Action Fund and a former acting assistant secretary of energy. His blog, called "Climate Progress," has tracked the issue closely.
"My guess is that Obama, who is an incredibly competitive guy, was just annoyed at mockery and laughter and wanted to respond personally," Mr. Romm says. "But I also think that he's been trying to think about how to inject climate into the debate. Romney gave him an opening to do just that."
But there are also indications that Obama, scratching for support among independent voters in Ohio, Iowa, and other swing states, may have been warming to the idea of once again more publicly embracing climate change.
"It's been easy for the other side to pour millions of dollars into a campaign to debunk climate-change science," Obama told Rolling Stone magazine in April. "I suspect that over the next six months, [climate change] is going to be a debate that will become part of the campaign, and I will be very clear in voicing my belief that we’re going to have to take further steps to deal with climate change in a serious way."