"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.'"
The best book on programming for the layman is "Alice in Wonderland";
but that's because it's the best book on anything for the layman.