World Resources Institute: The worlds two largest greenhouse gas emitters--the United States and China--have been forging a growing bond in combating climate change. Just last week, President Obama and President Xi made a landmark agreement to work towards reducing hydrofluorocarbons (HFCs), a potent greenhouse gas. And both the United States and China are leading global investment and development of clean energy. The United States invested $30.4 billion and added 16.9 GW of wind and solar capacity in 2012. China invested...