Nitrous oxide, commonly known as laughing gas, is a chemical compound with the formula N2O. At room temperature, it is a colorless non-flammable gas, with a slightly sweet odor and taste. Nitrous oxide is a greenhouse gas, accounting for around 6% of the estimated heating effect of greenhouse gases in the atmosphere. According to 2006 data from the United States Environmental Protection Agency, industrial sources make up only about 20% of human caused industrial sources. Other human activity may account for 30%; tropical soils and oceanic release account for 70%. Human-caused nitrogen loading to river networks is a potentially important source of nitrous oxide emission to the atmosphere which may have been severely underestimated. It happens via a microbial process called denitrification, which converts nitrates to nitrous oxide and other gases.