Climate Central: There was a huge global spike in one of the most potent greenhouse gases driving climate change over the last decade, and the U.S. may be the biggest culprit, according a new Harvard University study. The United States alone could be responsible for between 30 percent and 60 percent of the global growth in human-caused atmospheric methane emissions since 2002 because of a 30 percent spike in methane emissions across the country, the study says. The research shows that emissions increased the most...