Urban ecology in temperate climates. Greenhouse gas emissions include those of carbon dioxide and methane from the combustion of fossil fuels to supply energy needed by vast urban metropolises. Other greenhouse gases include water vapor, and nitrous oxide. Increases in greenhouse gases due to urban transport, construction, industry and other demands have been correlated strongly with increase in temperature. Sources of methane are agricultural dairy cows and landfills. Processes related to urban areas result in the emission of numerous pollutants, which change corresponding nutrient cycles of carbon, sulfur, nitrogen, and other elements. Ecosystems in and around the urban center are especially influenced
Nitrous oxide used by almost half a million young people at nightspots, festivals, and parties. The legality of that use varies greatly from country to country, and even from city to city in some countries. The major safety hazards of nitrous oxide come from the fact that it is a compressed liquefied gas, an asphyxiation risk, and a dissociative anaesthetic. While relatively non-toxic, nitrous oxide has a number of recognized ill effects on human health, whether through breathing it in or by contact of the liquid with skin or eyes. Nitrous oxide is a significant occupational hazard for surgeons, dentists, and nurses.