The United Nations welcomed on Wednesday a plan by U.S. President Barack Obama to attend a U.N. climate meeting in Copenhagen next month and urged rich nations to promise deeper cuts in greenhouse gas emissions. “It's critical that President Obama attends the climate change summit in Copenhagen,” Yvo de Boer, head of the U.N. Climate Change Secretariat said about Obama's plan to visit on December 9, near the start of the December 7 to the 18, meeting. “If he can deliver on his election campaign statements that Copenhagen needs to be a success by coming to Copenhagen himself, that I think will be critical to a good outcome,” he told a news conference webcast from Bonn, Germany, where the U.N. Climate Secretariat is based. De Boer said the world was looking to the United States to offer a goal for cutting greenhouse gas emissions by 2020 in Copenhagen and to contribute cash to help developing nations cope with global warming. He said that there had been “encouraging signals” in recent days, including a revised pledge by Russia to restrict emissions to 25 percent below 1990 levels by 2020. “But still the aggregate pledges do not match up to the level indicated as necessary by science,” de Boer said. “There is no time to lose.”