Reuters: The United States and China should hold a summit featuring an agreement on climate change, helping to create international support for a new global pact by the end of 2009, a former White House adviser said on Thursday. China and the United States have often been icy rivals over trade and security, and they are also the world’s top two emitters of the greenhouse gases from burning fossil fuels that are stoking global warming. Kenneth Lieberthal, a former National Security …