Methane is a chemical compound with the chemical formula CH4. It is the simplest alkane, and the principal component of natural gas. The abundance of methane in the Earth's atmosphere in 1998 was 1745 parts per billion, up from 700 ppb in 1750. Methane can trap about 20 times the heat of CO2. In the same time period, CO2 increased from 278 to 365 parts per million.