Hugh Pickens writes "The Christian Science Monitor reports that according to new research, nitrous oxide, the colorless, sweet-smelling gas with a long history as a medical and dental anesthetic is the next big threat to Earth's protective ozone layer. Its role in destroying ozone has long been recognized, as well as its role as a heat-trapping greenhouse gas but the new study puts nitrous oxide's ability to deplete ozone into numbers comparable to those used for other ozone-depleting gases covered by the 1987 Montreal Protocol. The researchers note that the health of the ozone layer has been improving since the adoption of the protocol and that nitrous oxide looms large today as an artificial destroyer of the ozone layer, in part because the emissions of other harmful chemicals have been so sharply reduced." (Continues.)"Globally, Earth's ozone layer has thinned by 5 to 6 percent since 1980, before CFCs and their ilk came into wide use, according to Akkihebbal Ravishankara, who led the study. He and his colleagues note that 6 percent may appear to be a small number, but it still can lead to significant effects on organisms at Earth's surface. The researchers did not make any policy recommendations in light of their finding. 'It is not for us to gauge how much risk there is,' says Ravishankara. In any event, Ravishankara says, at the moment researchers could not say with confidence 'how much nitrous oxide comes from where.'"