Capping a day-long futurist fair and alternative music fest on the South Lawn of the White House on Monday, President Obama told actor Leonardo DiCaprio and atmospheric scientist Katharine Hayhoe “we’re really in a race against time” to curb the worst affects of climate change.

The hour-long panel discussion, which was immediately followed the U.S. premiere of “Before the Flood,” a National Geographic documentary on climate change that DiCaprio starred in and produced, aimed to shift public opinion on an issue that even DiCaprio acknowledged rarely galvanizes voters.

As he introduced Obama and Hayhoe, who directs Texas Tech University’s climate science center, the Oscar winner said he and director Fisher Stevens wanted their film “to be released before this upcoming election because after firsthand experiencing the devastating impacts of climate change worldwide, we, like many of you here today, realize that urgent action must be taken.”

“This moment is more important than ever. We must empower leaders who not only believe in climate change but are willing to do something about it,” DiCaprio said. “The scientific consensus is in, and the argument is now over. If you do not believe in climate change, you do not believe in facts, or in science, or empirical truths, and therefore, in my humble opinion, should not be allowed to hold public office.”

Those lines, and others, drew loud applause from the crowd. And while the president endorsed the idea of “turning up the dials and reducing the amount of carbon pollution that we’re putting into the atmosphere,” Obama cautioned that incremental steps were essential to making meaningful progress.

Recalling that he often instructed his international climate negotiators and other aides that “better is good,” Obama said he understood some activists’ frustration. “Better is not always enough; better is not always ideal, and in the case of climate change, better is not going to save the planet.  But if we get enough better, each year we’re doing something that’s making more progress, moving us forward, increasing clean energy, then that’s ultimately how we end up solving this problem.”

Noting that most Americans rely on their cars to commute to work and to travel across the country, the president said, “And you can’t, overnight, suddenly just start having everybody taking high-speed trains because we don’t have any high-speed trains to take. And we have to build them. And we should start building them. But in the meantime, people have to get to work.”

The audience cheered the president’s initial reference to imposing a carbon tax, even though he cautioned, “the likelihood of an immediate carbon tax is a ways away.” But Obama suggested Americans should be extracting natural gas through fracking, which many liberal activists oppose because these operations emit the potent greenhouse gas methane and potentially pose a threat to nearby drinking water supplies.

“And I get all that,” he said. “On the other hand, the fact that we’re transitioning from coal to natural gas means less greenhouse gases.”

Neither Obama, who relies on the presidential aircraft to travel with an extensive entourage nearly every week, nor DiCaprio, who travels at times on private planes and yachts, addressed their own considerable carbon footprints.

Stevens said in an interview that the film’s backers paid a voluntary carbon tax to offset the greenhouse gas emissions involved in traveling to China, India, Greenland, the Arctic, Indonesia, Micronesia and multiple cities in the United States and Europe. The money, which he said was in “the tens of thousands” of dollars, will support reforestation projects in areas such as Brazil, Indonesia and Mexico.

With many audience members sitting on red-and-black plaid woolen blankets on the lawn on a balmy evening and a warm-up performance by the Denver-based band the Lumineers, the gathering felt at times like a genuine music festival. But the wonky crowd was clearly more focused on the panel discussion than many of the acts that had preceded it, erupting into loud cheers when DiCaprio made a reference to Obama’s broad use of the 1906 Antiquities Act to protect federal lands and waters.

Hayhoe, for her part, said people who are invested in cutting greenhouse gas emissions need to recognize that they will not win converts by lecturing people who are skeptical.

“The biggest thing I’ve learned is facts are not enough,” she said, “In fact, the more literate we are about science, the more polarized we are about climate change.”

“The most important thing to do is not to pile up scientific reports until they reach a tottering pile of about eight feet, where they’ll tip over and crush somebody,” Hayhoe continued. “The most important thing to do is to connect this issue to what’s already in our hearts.”

“So, in the case of climate change, if we could flip a magic switch and turn off all our carbon emissions today, we would still see the impact of the Industrial Revolution on our planet for well over 5,000 years. That’s how long we would see it,” she said. “But, on the other hand, there’s still plenty of time to avoid the worst of the impacts. If we act now.

In addition to meshing with the White House’s climate agenda, “Before the Flood” shows the extent to which the National Geographic Channel has not shifted ideologically since being purchased by Rupert Murdoch’s 21st Century Fox. Both the documentary and the second season of “Years of Living Dangerously,” a climate series that debuted on Showtime, will premiere on Oct. 30.

Joe Romm, who serves as chief science adviser for “Years of Living Dangerously” wrote in a recent blog post, “I can personally attest that this season’s science-driven episodes are every bit as blunt about the urgent nature of the climate crisis as Season 1 was.”

“Before the Flood” was produced independently and later acquired by National Geographic, but Stevens said the channel’s executives were supportive of his and DiCaprio’s desire to air it before most voters head to the polls in early November.

And at an event that focused on technologies that could transform life on earth, one of the funniest moments came when it emerged that one of the panelists had a backup plan–in space. Hayhoe, an observant Christian, noted that she has spent much of her career seeking to challenge the idea many hold “that I have to be a certain type of person to care about climate change. And if I am not that person, then I don’t care about it because I care about these other things.”

“But the reality is, is that if we’re a human living on this planet–which most of us are–as long as we haven’t signed up for the trip to Mars–I don’t want to know if anybody has. I think you’re crazy,” she added, as the crowd laughed.

“I did,” DiCaprio interjected.

“Oh, you did?” Hayhoe responded. “Oh, I’m sorry, I take that back.”

“I think you’ll acknowledge he’s crazy,” the president chimed in, as the audience laughed once more.

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