World leaders attending the UN’s Rio+20 sustainability summit appear prepared to rubber-stamp an agreement that has been widely criticized by environmental groups and some government officials as ineffectual. As Chinese Premier Wen Jiabao, Russian President Vladimir Putin, U.S. Secretary of State Hillary Clinton, and other leaders arrived in Rio, participants at the conference seemed resigned to approving an agreement that fails to set concrete goals, timetables, or methods of financing for ensuring environmentally sustainable economic growth, particularly in the developing world. “Let me be frank — our efforts have not lived up to the measure of the challenge,” UN Secretary-General Ban Ki-moon said in opening remarks. “Nature does not wait. Nature does not negotiate with human beings.” Government officials and diplomats said that the host country, Brazil, was determined to avoid the chaos that surrounded the failed climate talks in Copenhagen in 2009. As a result, delegates from 193 countries drafted a non-committal agreement that heads of state are expected to sign with few changes on Friday.