A greenhouse gas (GHG) is any gaseous compound in the atmosphere that has the capability to absorb infrared radiation, hence trap it leading to an increase in heat in the atmosphere. Trapping heat in the atmosphere has a green house effect, and hence gases able to do this are regarded as greenhouse gases, and this phenomena ultimately leads to global warming
Greenhouse gases are categorized into two groups namely direct and indirect GHGs
Direct GHGs include
1. Carbon dioxide (CO2)
2. Methane (CH4)
3. Nitrous oxide (N2O)
4. Hydrofluorocarbons (HFCs)
5. Perfluorocarbons (PFCs)
6. Sulphur hexafluoride (SF6)
7. Nitrogen trifluoride (NF3)
The GHG making the greatest contribution to climate change is carbon dioxide and that is why it is the main focus in climate change initiatives. Methane and nitrous oxide contribute to a lesser extent at about 10%.
HFCs, PFCs, SF6 and NF3 are collectively have high Global Warming potential but their contribution to climate change is very small at less than 5%.
Direct GHG, are regarded as ‘emissions from sources that are owned or controlled by an organization’. Their sources include
1. Stationary combustion of fossil fuels such as natural gas, fuel oil etc. for heating or other
domestic and industrial applications
2. Mobile combustion of fossil fuels (e.g. gasoline, diesel) used in mobile transportation such as
3. Process emissions released during the manufacturing process within the industry sectors (e.g.
cement, iron and steel, ammonia)
4. Fugitive Emissions which refers to unintentional release of GHG from sources including
refrigeration, and natural gas distribution
Institutions differ in terms of relevance and hence levels of contribution to pollution from the 4 sources of GHG emissions.For instance, majority of organizations score highly on stationary and mobile combustion sources.
Indirect GHG emissions emanate as a consequence of the activities of the organization that reports on its emissions. Their sources could be traced to facilities or practices owned or controlled by another entity. Indirect GHGs emanate from operations of an organization but are not directly owned or controlled by the organization. For instance, indirect GHGs emanating from the energy sector include those ‘emissions emanating from consumption of purchased electricity, steam, or other sources of energy not generated from the organization’.
Other sources of indirect GHG sources include :
• employee business travel
• transportation of products, materials, and waste
• outsourced activities, contract manufacturing, and franchises
• emissions from waste generated by the institution when the point of GHG emissions occurs at sources or sites that are owned or controlled by another company, e.g. methane emissions from landfilled waste
• emissions from the use and end-of-life phases of products and services produced by the institution
• employees commuting to and from work
• dealing with imported materials
Indirect GHGs form the bulk of emissions from most organizations and constitute their largest carbon footprint
Other indirect Greenhouse gases includes
1. Nitrogen oxides (NOx)
2. Carbon monoxide (CO)
3. Non-methane volatile organic compounds (NMVOC)
4. Sulphur dioxide (SO2)