: Despite the success of the 1987 Montreal Protocol in limiting the production of manmade chlorofluorocarbons (CFCs), scientists have discovered four new gases
that threaten the ozone layer: Three are CFCs and one is a hydrochlorofluorocarbon. Where the gases are coming from is unknown. By analyzing the air trapped in polar snow pack and comparing it with modern air samples, Johannes Laube of the UK’s University of East Anglia and colleagues have determined that the four mystery gases first appeared in the 1960s, which suggests they are manmade. Although the concentrations at this point are relatively small, the gases can hang around for a long time, so steps must be taken to prevent dangerous concentrations from accumulating.