Waste burning is a major source of dangerous carcinogens such as dioxins and furans, as well as black carbon, a short-lived climate pollutant that contributes to climate change, increased melting in polar regions due to soot and black carbon deposition on snow and ice, and a variety of human health issues. Burning trash also produces nitrogen oxides and volatile organic compounds that can lead to new pollution problems. Dioxins are known human carcinogens that can cause developmental defects, immune system deficiencies, liver damage, and other health concerns. Furans are similar to dioxins but are more toxic. Black carbon is responsible for much of the global warming impact of fossil fuels like gasoline and diesel because it absorbs heat from sunlight that would otherwise reach earth's atmosphere. It also has a long lifetime that can lead to soil erosion and water contamination. Nitrogen oxides contribute to ground level ozone which can lead to asthma attacks and premature death. They're also linked to acid rain and smog. Landfills also emit harmful substances into the environment. Landfill gas, or natural gas, is composed of approximately 50% methane with smaller amounts of other gases including hydrogen sulfide, carbon dioxide, and others. The main component of landfill gas is naturally occurring methane, which is odorless, colorless, and non-toxic. However many landfills leak gas at some point during their operation.