Associated Press: Scientists are working to pinpoint the source of a giant mass of methane hanging over the southwestern U.S., which a study found to be the country's largest concentration of the greenhouse gas. The report that revealed the methane hot spot over the Four Corners region where Colorado, New Mexico, Utah and Arizona meet was released last year. Now, scientists from the University of Colorado, the University of Michigan, the National Oceanic and Atmospheric Administration and NASA are conducting...