The United Nations environmental conference in Rio de Janeiro wraps up Friday, with representatives of more than 190 countries pledging to take action to promote sustainable development and lift billions of people out of poverty.

Speaking on the third and final day of the Rio+20 summit, U.S. Secretary of State Hillary Clinton called for new and “different” thinking to preserve the world's resources, telling leaders they “cannot afford to fail.”

“So we have come together here in Rio to identify practical ways we can all promote sustainable development, and while our views may differ sometimes, I believe we agree on some fundamental principles. We cannot be boxed in by the orthodoxies of the past, we should and must make decisions based on research and scientific evidence about what works and above all, we need fresh, agile, action-oriented partnerships that can produce results year after year after year.''

Environmental activists have criticized the summit in the Brazilian capital, saying the outcome document approved by diplomats is too weak, lacks specific commitments and makes little progress.

Clinton said officials know they will be judged not by what they say or intend, but by whether they deliver results.

She highlighted U.S. efforts to tackle deforestation, water, solid waste and food security issues, and announced $20 million in grants to support clean energy in Africa.

“Earlier today, I helped launch a partnership between the United States and African nations that will use $20 million in U.S. government funding to unlock hundreds of millions of dollars in private financing for clean energy projects in Africa and beyond. It's part of our contribution to the United Nations' Sustainable Energy for All initiative, which has secured significant private sector investments for sustainable energy. And we hope to see even more coming out of Rio.”

On Thursday, U.N. Secretary-General Ban Ki-moon said more than 50 governments have been developing new energy strategies under the Sustainable Energy for All initiative. And he said private investors have committed more than $50 billion toward the initiative's goals of ensuring universal energy access, doubling the rate of energy efficiency and sharing global renewable energy by 2030.