Well, what do you know, President Obama can say the C word after all. Until last night’s speech at the Democratic National Convention, “climate change” had virtually disappeared from Obama’s public vocabulary. So it was a surprise to hear him affirm that, “yes, my plan will continue to reduce the carbon pollution that is heating our planet, because climate change is not a hoax. More droughts and floods and wildfires are not a joke. They are a threat to our children’s future.”

The president was obviously drawing a contrast with Mitt Romney, whose speech at the Republican National Convention last week mocked the very idea of caring about climate change. “Four years ago, President Obama promised to begin slowing the rise of the oceans,” the Republican nominee said as the party faithful chortled. “And heal the planet,” Romney added to further laughter. “My promise is to help you and to your family.”

The Romney campaign apparently plans to make this attack a continuing theme. Two days later in the battleground state of Ohio, Romney repeated it, demonstrating once again how extreme today’s Republican party has become. Even George W. Bush, for all his resistance to tackling climate change, never made fun of it.

“It is nothing short of terrifying to imagine a party that openly mocks climate change taking back the White House,” the Obama campaign fired back via e-mail. True enough. But the president’s own statements, before last night, have not been terribly reassuring either, if only because there have been so few of them. Ever since his cap-and-trade legislation crashed and burned under intense Republican fire in 2010, Obama has avoided the term “climate change” in public.

So does his convention speech signal that Obama will now champion the climate fight? Or was he merely punching back at Romney and telling the Democratic base what they wanted to hear?

Some historical perspective might be useful. For decades, Democratic politicians have shunned the “L word”: liberal. For most of his presidency, and especially for the past two years, Obama has done the same with the C word. Aside from his acceptance speech, and three much briefer mentions in speeches to university audiences in Virginia, Colorado and Iowa the week before, Obama appears not to have brought up “climate change” publicly a single time in 2012. (Yes, he used the term in his interview with Rolling Stone in April, but only after the interviewer raised the subject.)

The White House press office did not respond to a request for a list of president Obama’s mentions of climate change.

The president has preferred to talk instead about “clean energy.” And as in his acceptance speech last night, he usually does this in the context of advocating an “all of the above” energy strategy: exploiting all available sources, including oil, gas and what he (inaccurately) calls “clean coal.”

Obama told Rolling Stone he expected climate change would be an issue in the presidential campaign, and he promised to “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.” Except then he didn’t.

It hasn’t been for lack of opportunity. Beginning in June, the United States has suffered one of the hottest summers and worst droughts in its history, sparking wildfires and stunting crops. Meanwhile, the Arctic ice cap has melted to its lowest level on record. Talk about terrifying. When white ice is replaced by dark seawater, more of the sun’s heat is absorbed rather than reflected, accelerating global warming. The loss of Arctic ice is the “equivalent of about twenty years of additional carbon dioxide being added by man,” Peter Wadhams, a professor of ocean physics at the University of Cambridge, told the BBC.

All the while, Obama remained silent. Even as his own government’s scientists were affirming climate change’s connection to the extreme weather events of 2012, the president declined to use his bully pulpit to make the connection clear to the public, much less attempt to rally Americans to action.

Of course, Obama has had a lot on his plate, above all a sluggish economy and high unemployment. But nothing else will matter if the planet becomes uninhabitable, and it’s not hyperbole to say that this is the course humanity is on. If current emissions trends continue, global temperatures will increase by six degrees Celsius by 2100, warns the International Energy Agency. “Even schoolchildren know this will have catastrophic implications,” said the IEA’s chief economist, Fatih Birol.

Obama must know this, too; certainly his science advisers do. Perhaps that’s why he chose to utter the C-word again in Charlotte.

But there is much further to go, and the good news is that the political terrain for the climate debate may be undergoing a shift. The conventional wisdom, apparently shared until recently by Obama and his political advisers, has assumed that talking about climate change turns voters off: it’s too dark, too controversial, too complicated. But a growing body of evidence challenges this view. Speaking out about climate change—and above all about how to fight it—can be a political winner, the argument goes, in part because the hellish summer of 2012 has led many more Americans to think that climate change is real and dangerous after all.

“I think we have achieved a real tipping point with the public, in that they finally see for themselves what the reality of climate change means,” said Joe Romm, editor of the nation’s leading climate science blog, Climate Progress. In his new book, Language Intelligence, Romm explains how the use of rhetorical tools such as repetition, irony and above all metaphor can sharpen advocates’ persuasiveness on any subject, including one as wonky as climate change. Romm says, “You can’t say one individual home run was due to steroids, but when somebody gets seventy in one season, then you understand what it means for them to be juiced. Our climate has been juiced by the steroids of greenhouse gases, which make almost every major extreme weather event more extreme.”

“Three out of four Americans now acknowledge climate disruption is real, and more than two out of three believe we should be doing something about it,” declares Climate Solutions For A Stronger America, a new report intended to help activists, public officials and other advocates build public support for climate action. (Disclosure: the report’s sponsor and writer, Betsy Taylor, head of the consulting firm Breakthrough Strategies and Solutions, is a friend of the author.) Climate Solutions For A Stronger America draws on numerous opinion polls, notably a new nationwide poll of 1,204 likely voters that was conducted specifically for the report by Harstad Strategic Research, Inc., which was Barack Obama’s pollster when he was a senator and still does contract work for him as president. Among the poll’s other findings was that “a pro-climate action position wins votes among Democrats and Independents, and has little negative impact on Republican voters.”

The narrative advocates can use to mobilize such voters, the report suggests, is the classic quest story: heroes set off to vanquish villains in service of the common good. “Americans don’t run away from big challenges,” goes the script. “We turn them into big opportunities. We have a responsibility to our kids. But Big Oil and the Koch brothers are standing in the way: corrupting our political process and blocking American clean energy innovation. It’s time to take our future back, and clean energy’s a great way to do it.”

In 2008, it looked as though Barack Obama would be the hero to lead such a quest. Now, his speech in Charlotte has raised hopes among some environmentalists that Obama, after an extended absence, may be ready to rejoin the battle. That would be a good thing. But if four years of Obama’s presidency demonstrate anything, it is the folly of waiting for him, or any president, to storm the barricades of entrenched power. If America is to vanquish the climate villains and win the quest for survival, we the people will have to be our own heroes.