U.S. Special Envoy for Climate Change Todd Stern threw cold water yesterday on green groups' hopes of luring President Obama to this summer's environmental mega-conference in Rio de Janeiro.

Speaking from Rome, where he and representatives from 17 countries met as part of a Major Economies Forum to discuss the international global warming negotiations, Stern said he does not believe the U.N. Conference on Sustainable Development, known as Rio+20, in June will have a significant bearing on the climate change treaty process.

And while activists have enlisted celebrities like Leonardo DiCaprio to generate more interest in Rio+20 among Obama and other world leaders -- and the United Nations' climate chief, Christiana Figueres, said yesterday she would like to see Obama attend -- Stern dismissed the possibility as unlikely.

"As far as I am aware, climate isn't going to be a big focus of Rio, certainly [not] in a way that would be relevant to the negotiations," he said. As for Obama's attendance, he said, "I don't have any understanding that the president has any intention of going."

The comments come as the United Nations works to whip up enthusiasm for Rio and organizers struggle to define common goals for the summit. More than 100 world leaders are expected to attend, as well as foreign ministers and global corporate executives.

Rio: a place for a 'bigger conversation'

Figueres, speaking at the U.N. Foundation in Washington, D.C., yesterday, also cautioned that Rio is not a technical negotiations process like the climate talks, and did not point to any potential outcomes that might help spur treaty discussions. But she championed the summit as a place for world leaders to have "a bigger conversation" about the environment rather than the nitty-gritty debates over how many tons of carbon dioxide must be eliminated from the atmosphere.

"Rio is about a dialogue, a conversation about what kind of society do we really want," Figueres said. When asked if she'd like to see Obama there, she said, "I would definitely like to see all presidents come to Rio. ... I think a conversation as important as what kind of society are we now willing to construct does have to be at the level of leaders of all countries."

Meanwhile, the Natural Resources Defense Council is asking young people to "help encourage" Obama and others to show up in Rio. It is sponsoring a contest asking would-be videographers ages 13 to 30 to address how nations attending this summer's "date with history" can best improve the state of the planet.

An online vote will determine regional finalists, after which DiCaprio will be joined by U.N. Foundation President Timothy Wirth, actor Hayden Panettiere, former Brazilian Environment Minister Marina Silva and Figueres as judges.

The contest clearly addresses worries in the activist community that interest in Rio is running low. In a blog post last week, Jacob Scherr, NRDC's director of global strategy and advocacy, wrote that he has "been struck by the lack of urgency and energy in the formal discussions" leading up to the conference.

"It appears that governments will spend thousands of hours this spring arguing over a draft Rio+20 output document now more than 200-page long," he said. "We heard for the first time people worried that Rio could turn into another Copenhagen."

In subsequent interviews, Scherr and NRDC spokesman Bob O'Keefe were asked exactly how the group is pressuring Obama to attend. They said NRDC is talking to White House staff and the State Department to lean on the president to fly to Brazil.

Figueres and Stern both said they believe the climate negotiations are on track as countries work to develop a legal agreement that will bind all nations to cut carbon. Under the Durban Platform, which countries agreed to in South Africa last year, that agreement -- the legal form of which is still under discussion -- will be agreed to by 2015 and take effect in 2020.

Delegates will meet in Bonn, Germany, in May for the first formal negotiating session since Durban to set an agenda. Figueres said the main goals this year will be for countries to enter targets for a second commitment period of the Kyoto Protocol and decide how many years that window should last, as well as to finalize decisions about where to host the Green Climate Fund and a new clean technology center and to submit reports on how to best raise the $100 billion annually that some nations promised in aid.

Figueres also leaned on countries to increase the emission targets they offered at the 2009 Copenhagen, Denmark, climate summit.

"We cannot go into 2020 with the ambition we have at this moment on the table," she said, and argued that U.N. goals of eliminating energy poverty while increasing efficiency and renewable power can help that goal. "The important thing here is to demonstrate that raising ambition has a whole host of opportunities and benefits. If it's only seen as a burden, we're not going to get there."

Yet Figueres also said that the concept of "historical responsibility" for causing climate change will be a central pillar in assessing what level of ambition nations take. The United States, which has emitted the most carbon dioxide for the greatest number of years, is understood by nearly every international measure to bear the biggest responsibility under that equation.

Hopes for Doha talks

Stern -- who in the past has roundly rejected the idea pushed by climate change activists that the United States owes a climate or ecological "debt" to the world for its past pollution -- yesterday also appeared to minimize the notion of historical responsibility and the role that issues of equity will play in the future.

"I don't share Christiana's view that that's a driving force for these negotiations. I think the driving force is going to be that we have to find a way to make the new agreement inclusive and relevant to the world of the 2020s and satisfy the need to make the agreement be potent in responding to the challenge of climate change," he said.

He described the phrase "historical responsibility" as "a concept that some have affection for." And, he said, while countries of different degrees of wealth and historical emissions won't be expected to cut the same level of emissions post-2020, he does expect what he called "comparable" efforts.

He described the Major Economies Forum talks as a "good initial discussion" and said countries largely agreed that 2012 and the year-end conference to be held in Doha, Qatar, should be focused on studying how to develop a new framework that holds all countries to account for emissions. Under the 1997 Kyoto Protocol, which the United States did not join, only industrialized countries were obligated to curb carbon, but by 2020, according to the Durban agreement, all nations will be subject to legally binding cuts.

"I don't think anybody's thinking there's going to be any big deliverable in Doha or big negotiating text or anything like that," Stern said. "People are quite mindful that we're entering new terrain here."

He did caution that tension over Europe's decision to charge foreign airlines for their carbon emissions could infect the climate negotiations. Nearly two dozen nations, including the United States, China and India, have fought the European Union's decision to bring airlines into the bloc's Emissions Trading System (ETS).

"There is a risk that there will be some spillover effect if the ETS issue isn't resolved. It's got that potential," Stern said. He noted that there were several mentions of the airline issue at the Rome meeting, all "uniformly negative," and indicated the frustration could seep into treaty talks.

"Quite a few countries, and I'm not even talking about the United States right now, are quite upset about the ETS and upset about what, in their judgment, it says about the multilateral system or the disregard for that system, however difficult it might be to operate," Stern said.

He noted that Europeans charge that the United Nations' International Civil Aviation Organization has been unable to make progress on a more comprehensive emissions plan. But, Stern said, "The fact that it's difficult doesn't mean you throw this multilateral system or any other system in the trash can."