Rio+20 Brazil environment conference gearing up RIO DE JANEIRO - The United Nations on Monday prepared to launch its biggest conference in history, as delegates from around the world worked on a plan to help lift billions of people out of poverty without exhausting the planet. More than 115 presidents, prime ministers and other officials are to attend the U.N. Conference on Sustainable Development, which officially begins Wednesday and has drawn at least 50,000 people from 190 countries. Yet expectations remain low because of the world's many economic woes. "The European debt crisis, U.S. joblessness and even the Chinese economic slowdown has sapped some people's enthusiasm," said Timothy Wirth, president of the United Nations Foundation. President Obama has no plans to attend the conference. Secretary of State Hillary Rodham Clinton will lead the U.S. delegation, along with EPA Administrator Lisa P. Jackson and Todd Stern, a special envoy for climate change. Negotiators worked into the night Monday trying to finalize a master plan for social progress and managing natural resources. They hope to finish before Wednesday, when many international leaders plan to arrive to review proposals to slow down environmental degradation while providing enough food, water and clean energy for a worldwide population of 7 billion that's expected to reach 9.3 billion by midcentury. "This is a once-in-a generation opportunity," saidU.N. Secretary-General Ban Ki-moon, who has been pushing to move beyond political promises and begin accomplishing goals. Yet criticism has mounted in recent weeks over the details, with detractors raising concerns that the plan is being watered down and could result in weakened commitments from world leaders. Former Soviet President Mikhail Gorbachev, who was at the conference Monday, joined others who have complained that the plan appears to be backsliding on commitments for deep cuts in carbon dioxide emissions and other greenhouse gases needed to avoid tipping into a danger zone of climate-related floods and droughts. Jacob Scherr of the New York-based Natural Resources Defense Council attended the first Earth Summit in Rio in 1992 and the follow-up meeting a decade later in Johannesburg, South Africa. He's back in Rio watching a messy process that he said demonstrates how difficult it is "to get 190 countries to negotiate and agree to a plan that will result in real action." The first Earth Summit 20 years ago was filled with promise, as nations supported international agreements to protect biological diversity and establish a framework to curb climate change. About 180 nations signed off on a long list of goals and agreements, including a plan for the 21st century called Agenda 21, which instituted long-term planning for sustainable development and an agreement to halt the advance of deserts claiming farms and grazing land. Since then, little progress has been made. Deserts continue to expand. The loss of plant and animal species has accelerated, with scientific tallies showing one-fifth or more of all species of mammals, birds and amphibians now at risk of extinction. And greenhouse gases have continued to build up in the atmosphere, despite ongoing deliberations under the climate convention, which included the Kyoto Protocol, and a series of unsuccessful efforts to negotiate a new climate treaty. The U.N. Environmental Program examined more than 500 internationally agreed-upon goals and objectives adopted at the Earth Summit and other such meetings. It found this month significant progress in just four: eliminating chlorofluorocarbons that punched a hole in the Earth's protective ozone layer, the removal of lead from gasoline that caused human health problems, improved access to clean water, and boosting research to reduce ocean pollution. Nikhil Seth, the U.N. director of sustainable development, said the U.N. Environmental Program report illustrates the need for this week's conference, known as Rio+20, to refocus the world's attention on important, long-term issues. "We're depleting everything," Seth said, "the land we depend on to grow food, the air we need to breathe, the oceans we need for fish."