It was a rich, if abbreviated exchange.
"President Obama promised to begin to slow the rise of the oceans," declared Mitt Romney, the Republican presidential hopeful, at the party's convention late last month.
He paused to allow disdainful hoots and laughter to infect the crowd.
"And to heal the planet."
Whether it was meant as a jab at global warming itself, which many conservatives consider a non-issue, or at President Barack Obama's fondness for highfalutin oratory -- or perhaps both -- is unclear, but Romney enjoyed the quip enough that he has since repeated it.
The president offered his reply a few days later, during his speech at the Democratic convention.
"Climate change is not a hoax," Obama said. "More droughts and floods and wildfires are not a joke. They are a threat to our children's future, and in this election you can do something about it."
Taken together, this back-and-forth provided a clear, albeit clipped, staking out of ground on an issue that, in the view of many observers, had otherwise fallen off the map in this historic presidential race.
Much more discussion, climate activists say, is needed.
"Nobody is speaking out in a sufficiently loud way," said Bill McKibben, the founder of the climate change advocacy group 350.org. "We just came through a summer that saw the warmest month ever recorded in American history -- July. There's never been any month in any year warmer than that. And as far as I know, that went entirely unremarked by any of our political leaders."
Such is the premise behind a website launched Thursday morning by a pair of organizations hoping to nudge climate change into a more prominent place in the campaign dialog. The site, ClimateSilence.org, argues that both Romney and Obama have shifted, softened or otherwise toned down their public statements on the problem in "a collective descent toward mute acceptance of global calamity."
The site charts a selection of public statements made by both men over the last five years or so, and sets them against a tonal spectrum that ranges from actions, promises or affirmation of the issue on one end, to avoidance, denial and exacerbation on the other.
"It's true that both do talk about climate change from time to time -- Obama more than Mitt Romney, and in a different way," said Brad Johnson, the campaign manager for the climate coverage watchdog group Forecast the Facts, which mounted the site in cooperation with Friends of the Earth Action, an environmental lobby group. "There's a real kind of differentiated gap in how they both talk about it, but it has changed over time," Johnson said. "There's been a real sort of decline in ambition and specificity and seriousness from both candidates."
That's probably not very surprising to many followers of Romney, who has equivocated for years on the issue, depending on his audience and agenda. But Johnson and others argue that even the president has failed to maintain the sense of immediacy and purpose he brought to the issue in, say, 2008, when he declared that "[f]ew challenges facing America -- and the world -- are more urgent than combating climate change."
When asked about these concerns, the White House pointed to a long list of Obama policy initiatives aimed at combating global warming -- from increased fuel economy for cars to historic curbs on power plant emissions and massive investments in clean-energy technology -- and to numerous recent instances where the president has mentioned climate change in public statements.
"President Obama has long focused on ways to develop clean energy as a core economic pillar," Adam Fetcher, a spokesman for the Obama presidential campaign, said in an email. "By advocating for the growth of renewable energy, President Obama has continually called for action that will address the sources of climate change."
The campaigners behind ClimateSilence.org aren't buying that, and they say they want a more robust, more frank discussion of the issue.
"Voters deserve to hear what our presidential candidates propose to do to lead the country on addressing this catastrophic problem," said Erich Pica, president of Friends of the Earth Action, in an emailed statement. "The candidates may differ on approaches to the problem, but anyone who is elected to lead the country, or aspires to do so, should realize that true leadership means a willingness to engage difficult issues, not sweep them under the rug."
If that seems overwrought, it's worth taking note of an ambitious roundup of the very best scientific evidence, issued just this week by Democratic Reps. Edward Markey of Massachusetts and Henry Waxman of California. The report was unequivocal in its conclusion that climate change is not some distant concern, but a clear and very present danger -- and one already contributing to loss of life and substantial economic costs.
"All weather events are now impacted by climate change to some degree because the underlying conditions that give rise to weather have been changed," the report stated. "Climate change has contributed to shattered records and unprecedented weather catastrophes, like those the United States has experienced this summer. It's as if global warming has stacked the deck with extra jokers, making some weather events more frequent and severe and increasing the chances of an event far outside the norm."
I asked Eben Burnham-Snyder, a spokesman for the House Natural Resources Committee, which co-authored the report, whether the tenor of the climate debate in campaign 2012 was off.
"When the GOP standard-bearer uses climate change as a punchline in his convention speech," he said, "then the debate over climate change action is certainly a concern."