Reuters: Levels of a powerful greenhouse gas are four times as high as previously thought, according to new measurements released on Thursday. New analytical techniques show that about 5,400 metric tons of nitrogen trifluoride are in the atmosphere, with amounts increasing by about 11 percent per year. Ray Weiss of the Scripps Institution of Oceanography in La Jolla, California, and colleagues said it had not been possible to accurately measure this gas before. They said nitrogen …