Among the basket of gases considered to be a contributor to global warming, nitrous oxide (N2O) accounts for about 6 percent of the heating effect of greenhouse gases in the atmosphere. Nitrous oxide also causes ozone depletion. Studies suggests that N2O emission currently is the single most significant ozone-depleting substance and is expected to remain the largest throughout the 21st century. Nitrous oxide is released to the atmosphere through agricultural nitrate fertilizers. The gas is also used in hospitals as anesthesia.