Stormwater retention ponds, a ubiquitous feature in urban landscapes, are not a significant source of climate-warming nitrous oxide emissions, a new study finds. Nitrous oxide is a potent greenhouse gas that contributes to global warming and destroys stratospheric ozone. Previous studies suggested stormwater ponds might be a problematic source of the gas, since they produce it as a by-product of the denitrification process that removes excess nitrogen from urban runoff.