Washington Post: The United States joined its allies Tuesday in committing for the first time to try to cut greenhouse gas emissions in half by 2050, as the Group of Eight nations approved a plan aimed at spurring a new worldwide treaty to limit global warming. In a statement on climate change, President Bush and the other G-8 leaders said they would work with other countries to “consider and adopt” the 50-percent reductions as part of a new United Nations treaty to be negotiated in …