The simplest hydrocarbon, methane, is a gas (at standard temperature and pressure) with a chemical formula of CH 4. However, when averaged over 100 years each kg of CH4 warms the earth 23 times as much as the same mass of CO2. Methane is a GHG with a relatively short atmospheric lifetime of 10+ years. The primary sources of methane are landfills, coal mines, natural gas systems and livestock.