emission of greenhouse gases
Greenhouse gases are naturally present in the atmosphere in order to keep the earth warmer by trapping some of the sun's rays on earth. Greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, ozone, chlorofluorocarbons, and hydrofluorocarbons.
Human activities contribute to the emission of greenhouse gases in the atmosphere through fossil fuel use, industrial processes, and intensive livestock farming, among others. Emission of large amounts of greenhouse gases can increase their natural levels in the atmosphere, possibly resulting to global warming.