An upcoming environmental mega-conference marking the 20th anniversary of the groundbreaking Rio Earth Summit has "the potential to really change the world," U.S. Department of Energy Assistant Secretary David Sandalow said yesterday.

The U.N. Conference on Sustainable Development, otherwise known as Rio+20, is being billed as an opportunity for world leaders to address major environmental concerns without getting mired in the fractious politics that snarl global climate change negotiations.

Yet the summer conference in Brazil's second-largest city has been beset by its own challenges, analysts said, including "meeting fatigue" and a still-unclear sense of what can be achieved.

Speaking at the Woodrow Wilson International Center for Scholars yesterday, experts described a conference of heads of state and top ministers as well as industry and environmental groups -- which somehow must avoid the pitfalls of previous green gabfests.

"Nobody really knows what is going to happen at this conference," said Robert Engelman, president of the Worldwatch Institute. "Governments don't seem too excited about it, and there's no real budget for it at the U.N."

Even Sandalow, despite his effusiveness, spoke only in broad generalities about concrete Rio+20 outcomes. He said the conference needs to be "more than a meeting of national governments." Rather, he added, governments, industry and others must build partnerships to deliver energy access to the world's poorest while increasing energy efficiency and renewable energy.

Reid Detchon, vice president for energy and climate at the U.N. Foundation, said he also believes the Rio de Janeiro conference can take concrete steps toward ending energy poverty and vastly expanding clean energy.

Detchon said he expected to see industrialized and developing country governments alike make commitments in Rio on issues ranging from investment finance for clean energy development to lifting certain tariffs for environmental products to adopting energy-efficient appliance standards. The Norwegian government is also expected to announce a partnership with five or six countries to encourage renewable energy development, he noted.

Rio+20 he maintained, will "set a new marker" on energy access, saying, "People will say that's where the world committed to sustainable energy for all."