Agence France-Presse: The White House pledged Friday to clamp down on US emissions of methane, a greenhouse gas produced by cattle and natural gas production that contributes to climate change. The bid is the latest by President Barack Obama's administration to find ways to tackle climate change in the face of staunch opposition by rival Republican lawmakers. The United States is the largest greenhouse gas emitter after China. Methane makes up some nine percent of US emissions but the environmental effect is some 20...