Reuters: U.S. President Barack Obama’s administration promised to push for a new United Nations climate treaty on Sunday but said Washington had no magic wand and that all countries had to help. “The United States is going to be powerfully and fully engaged,” U.S. special envoy for climate change Todd Stern said at the opening of 175-nation U.N. talks in Bonn, the first since Obama took office in January speaking of a “planet in peril.” “But we are all going to have to do this together, …