Greenhouse gases

Greenhouse gases act as an insulation layer to trap some of the sun's energy in the earth's atmosphere, between the earth's surface and this insulation layer. This is similar to the situation in a greenhouse - the glass walls allow heat and sunlight in during the day and trap it there so it can warm the plants that are growing inside.

This warming of the earth's surface makes life on earth possible - without it, the maximum daytime temperatures experienced by most areas on our planet would be similar to the temperatures experienced in space!

Diagram explaining the greenhouse effect

Graphic representation of the greenhouse effect
Source: CO2 Cooperative Research Centre

 

This YouTube video gives an overview of the greenhouse effect:

 

 

Why are people concerned?

Over the past 100 years or so there has been an increase in the amount of greenhouse gases in our atmosphere, causing an enhanced greenhouse effect. The increases in the concentrations of these gases are believed to be related to human activity: as human populations have increased over the past 200 years, so has demand for food and energy. This increased supply of food and energy has resulted in increased greenhouse gas emissions.

What are the main human sources of greenhouses gas emissions?

Carbon dioxide (CO2)

  • Production of electricity. In Australia, most of our electricity is generated by the combustion of large amounts of fossil fuels, and this process emits CO2.
  • Our transport needs. In Australia we rely heavily on motor vehicles for commuting and travelling and for providing services, like home deliveries. We use trucks and trains for long-distance transport of goods, and trains and planes for domestic and international travel. These modes of transport all burn fuel which results in CO2 emissions.
  • Land use change. When natural forest areas are cleared so that the area can be used for other purposes, for example agriculture, housing, industrial development or transport infrastructure the amount of CO2 in the atmosphere increases because there are fewer trees to store carbon in their timber and to convert carbon dioxide in the air to oxygen (O2) during the process of photosynthesis. Find out more about Carbon storage in forests.

Methane (CH4)

  • Livestock. Some of our domesticated livestock, such as cattle and sheep, produce methane during their digestion process. These animals provide us with some of our favourite foods, such as beef, lamb, milk, yoghurt and cheese. Australia's good reputation overseas for producing top quality food products has resulted in further demand for our agricultural livestock products, and hence increased livestock numbers, resulting in increased CH4 emissions.
  • Mining. Methane is released from the earth's core during mining operations for fossil fuels, which we use to provide energy for electricity. These emissions are called fugitive emissions.

Nitrous oxide (N2O)

  • Fertilisers. Nitrous oxide is emitted to the atmosphere during the production of fertilisers and after application to crops. Farmers use fertilisers to encourage quicker growth of pastures for livestock (grazing lands), and produce (crop lands). Our demand for fresh produce drives this industry.

 Allocation of greenhouse gas emissions

This figure shows greenhouse gas contributions by sector, and the types of activities which create the emissions.

Source: Australian national greenhouse accounts. National inventory by economic sector 2007. Department of Climate Change 2009. Copyright © Commonwealth of Australia - reproduced by permission.

Four primary industry areas 

For information on emissions associated with our four primary industry areas which supply us with our food, clothing, and energy, see:

 

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