It is no secret the networks of aging underground pipes in many big cities can be dangerous. Now, a new study has found they are also bad for the environment. Focusing their attention on Boston, a group of Harvard researchers writing in current issue of the Proceedings of the National Academy of Sciences found that $90 million worth of natural gas — 15 billion cubic feet — escapes from its network of aging cast iron pipes each year. That accounts for 60 to 100 percent of the region’s release of the methane, a potent heat-trapping greenhouse gas. Methane has a 25 times greater impact on climate change than carbon dioxide over 100 years. It only represents about 9 percent of U.S. emissions (compared to 82 percent for carbon dioxide), but that is growing, partly due to contributions from the oil and gas industry. “This study helps us better understand […]