Greenhouse gas accounting

The main greenhouse gases influenced directly by human activity are carbon dioxide, methane, nitrous oxide, ozone and synthetic gases such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFC).

Water vapour is also an important greenhouse gas, but its concentration in the atmosphere is not influenced directly by human activity: it is controlled mainly by the Earth's temperature.

The chemical properties of these gases make them effective in absorbing and reflecting the Sun's radiated warmth back into the atmosphere, rather than allowing it to pass through into space.

Each greenhouse gas has a different potential to warm the Earth; this potential is based on the gas’s 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 1 tonne of the gas will make to global warming over a 100-year period after it is emitted, compared with the warming caused by 1 tonne of carbon dioxide.

Source: Intergovernmental Panel on Climate Change, Climate Change 2013: The Physical Science Basis, 5th Assessment Report

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 gases used in refrigeration and air-conditioning

124 to 14,800

Perfluorocarbons (PFCs)

By-products of aluminium refining

7390 to 12,200

Sulfur hexafluoride (SF6)

Synthetic gas used in high voltage equipment

22,800


Using the GWP figure, emissions can be expressed in units of carbon dioxide equivalent (CO2-e). For example, 1 tonne of methane is 25 tonnes of carbon dioxide equivalent, or 25 tonnes CO2-e.

Where do emissions from human activity come from?

Sector

Activities

Stationary energy

Energy production

  • Combustion of fossil fuels for public electricity
  • Energy use in manufacturing industries and construction

Transport

Fuel combustion for 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 savannahs
  • 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

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

  • energy (the burning of fossil fuels)
  • industrial processes
  • solvent and other product use
  • agriculture
  • land-use change, land clearing and forestry
  • waste.

In Australia, emissions from solvents are ascribed to other sectors, and the fossil-fuel-burning energy sector is further broken down into:

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

For more information about NSW greenhouse gas emissions, visit the NSW Emissions Overview.

Further information: