Greenhouse gas accounting

The main greenhouse gases influenced directly by human activities are carbon dioxide, methane, nitrous oxide, ozone and synthetic gases, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs). Water vapour is also a major greenhouse gas, but its concentration in the atmosphere is not influenced directly by human activities: it is mainly controlled by the Earth's temperature.

The chemical properties of greenhouse gases mean that they strongly absorb and re-radiate the sun's warmth into the atmosphere. Each greenhouse gas has a different potential to warm the Earth, based on its chemical properties and how long it takes to break down in the atmosphere. Some take longer to break down than others. For this reason, each gas has been assigned a 100-year global warming potential (GWP) that uses carbon dioxide as the basis for measurement. The GWP for a gas identifies the relative contribution that one tonne of the gas will make to global warming over a 100-year period after it is emitted, compared with the warming caused by one tonne of carbon dioxide.

Gas	Main source	GWP (100 years)
Carbon dioxide (CO2)	Coal, oil, natural gas	1
Methane (CH4)	Coal mine fugitive gas, landfill	25
Nitrous oxide (N2O)	Manure, fertiliser	298
Hydrofluorocarbons (HFCs)	Synthetic gas used in refrigeration and air conditioning	124 - 14,800
Perfluorocarbons (PFCs)	By-product of aluminium refining	7,390 - 12,200
Sulfur hexafluoride (SF6)	Synthetic gas used in high voltage equipment	22,800

Source: Intergovernmental Panel on Climate Change, Climate Change 2007: The Physical Science Basis, 4th Assessment Report

Using the GWP, all emissions can be summed into a single carbon dioxide equivalent (CO₂-e) value. For example, emitting one tonne of methane is the equivalent of emitting 25 tonnes of carbon dioxide (25 t CO₂-e).

For more information about greenhouse gases and their global warming potentials, see Changes in Atmospheric Constituents and in Radiative Forcing in Climate Change 2007: The Physical Science Basis, contribution of Working Group I to the 4th Assessment Report of the Intergovernmental Panel on Climate Change.

Where do emissions from human activities come from?

The Intergovernmental Panel on Climate Change (IPCC) defines six sectors covering human-induced greenhouse gas emissions:

• energy
• industrial processes
• solvent and other product use
• agriculture
• land use change and forestry
• waste.

In Australia, emissions from solvents are ascribed to other sectors, and the energy sector (the burning of fossil fuels) is further broken down into:

• stationary energy (electricity and heating/cooling)
• transport
• fugitive emissions (fossil fuel gases escaping between the extraction of  the fuels and their burning).

For more information about the NSW greenhouse gas inventory, visit  emissions overview 2008.

 

Greenhouse gas sector	Activities included
Stationary energy	Energy production Combustion of fossil fuels for public electricity Energy use in manufacturing industries and construction
Transport	Fuel combustion in transport
Fugitive emissions	Mining and petroleum operations Underground mines Surface mines Oil and natural gas
Industrial processes	Metal production
Agriculture	Livestock and cropping operations Enteric fermentation (livestock emissions) Manure management Rice cultivation Agricultural soils Prescribed burning of savannas Field burning of agricultural residues
Land use, land-use change and forestry	Land clearing and forest production Land-use change: deforestation Land-use change: afforestation
Waste	Waste treatment Solid waste disposal on land (landfill) Wastewater handling Waste incineration

Greenhouse gas accounting in the land use, land-use change and forestry sector

Further information:

• Australia's position on land use, land-use change and forestry accounting
• how Australia accounts for greenhouse gas emissions