One of the first things scientists learned is that there are several greenhouse gases responsible for warming, and humans emit them in a variety of ways. Most come from the combustion of fossil fuels in cars, factories and electricity production. The gas responsible for the most warming is carbon dioxide, also called CO2. Other contributors include methane released from landfills and agriculture (especially from the digestive systems of grazing animals), nitrous oxide from fertilizers, gases used for refrigeration and industrial processes, and the loss of forests that would otherwise store CO2.

Where does greenhouse gas pollution come from?

Greenhouse gases are released into the atmosphere in many ways, including through the burning of fossil fuels (such as coal and petroleum) and by deforestation. As some environments warm (e.g. the Arctic tundra) they also release carbon that may have been stored for thousands of years.

Burning fossil fuels

greenhouse gas emissions come from the burning of fossil fuels for energy (e.g. for electricity and transport). When oil, gas or coal burns, carbon contained within it combines with oxygen in the air to create carbon dioxide.

Australia’s electricity-related emissions are high because we rely primarily (77%)1 on coal for electricity generation and coal is the most greenhouse-intensive fuel.

Deforestation: burning and removing vegetation

All plants take in carbon dioxide from the air and release oxygen, which is why they are sometimes referred to as carbon “sinks”. This process is called photosynthesis.

When land is cleared and trees or vegetation removed or burnt, the stored carbon is converted back into carbon dioxide.

Before European settlement in 1788, forest and woodlands covered 54% of Australia. This has now been reduced to 42%, mainly through landclearing2.

Farming

Animals, particularly sheep and cattle, produce large amounts of methane. Some fertilisers also release nitrous oxide, which is another greenhouse gas.

Waste breakdown

Carbon dioxide and methane are released during the decay of food, vegetation and paper dumped in landfills. The same thing occurs when sewage wastes break down.

Industry

Many industrial processes, such as cement production, liquid natural gas production and coal mining, produce or emit a variety of greenhouse gases.