Greenhouse Gas Emissions

What causes global warming?

Greenhouse gases (GHGs) trap heat in the atmosphere which causes global warming. There are four main types of greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N20) and high global warming potential (GWP) gases.

Carbon dioxide (CO2)
is released into the atmosphere primarily as a result of the burning of fossil fuels (oil, natural gas and coal) for power generation and in transportation. It is also emitted through various industrial processes, forest clearing, natural gas flaring and burning of organic matter. Some carbon is sequestered (captured/stored) in vegetation and agricultural soils which keeps it from collecting in the atmosphere.

Methane (CH4)
is produced primarily as a result of the decomposition of organic wastes in municipal solid waste landfills and from agricultural and biological processes related to wetland rice cultivation, livestock digestion and waste. Methane’s overall contribution to global warming is significant because it is estimated to be more than 20 times as effective at trapping heat in the atmosphere as CO2.


Nitrous oxide (N20)
is naturally produced in soils from microbial processes. Additions of nitrogen to soils by the agricultural sector increases the amount of N2O emitted. Nitrous oxide is also emitted during industrial production activities, solid waste combustion and fossil fuel combustion. Nitrous oxide is approximately 300 times more powerful than CO2 at trapping heat in the atmosphere.

High global warming potential (GWP)
gases include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6). HFCs are primarily used as replacements for ozone-depleting substances, such as chlorofluorocarbons (CFCs). PFCs and SF6 are emitted by a variety of industrial processes including aluminum smelting, electric power transmission and distribution, magnesium processing and semiconductor manufacturing.