What are greenhouse gases?
Greenhouse gases are a natural part of the atmosphere. It is the increase in the amounts of these gases through human activity that causes global warming. Human activity such as land clearing and burning fossil fuels have increased the concentration of these gases. Humans have had most impact on the enhanced greenhouse effect through increases in the amounts of carbon dioxide, methane and nitrous oxide.
Water vapour
Water vapour is the most important greenhouse gas, but human activity has little direct impact on the amount in the atmosphere.
Carbon dioxide (CO2)
The amount of carbon dioxide in the atmosphere is about 30% higher now than 200 years ago. The main causes of this increase are:
the burning of fossil fuels such as oil, coal and natural gas to create energy to make electricity and to produce fuel for transport, and
the clearing and burning of vegetation.
This gas is the biggest contributor to the enhanced greenhouse effect (about 70%)
Methane (CH4)
The amount of methane in the atmosphere is about 145% higher now than 200 years ago. The main causes of this increase are:
digestive processes of cattle and sheep (ie their burps!)
cultivation of rice
escape of natural gas
decomposing waste in garbage dumps or landfills.
This gas is the second biggest contributor to the enhanced greenhouse effect (about 20%)
Nitrous oxide (N2O)
The amount of nitrous oxide in the atmosphere is about 15% higher now than 200 years ago. The main causes of this increase are:
burning of vegetation
emissions from industries
the effects of agriculture on the soil (using nitrogenous fertilisers)
Halocarbons
These greenhouse gases have been reduced since the phasing out of chlorofluorocarbons (CFCs) to protect the ozone layer. However, other halocarbons effecting the atmosphere include perfluorocarbons (PFCs) emitted during aluminium production.
Fact sheet: Bad gas
How do we make greenhouse gases?
Burning fossil fuels
The burning of fossil fuels for energy (eg. for electricity and fuel for transport) generates the most greenhouse gases. When oil, gas, or coal burns, carbon in the fuel combines with oxygen from the air to form carbon dioxide. Methane is generated from coal mining and some natural gas pipelines.
Removing and burning vegetation
Growing plants absorb carbon dioxide from the air as part of their photosynthesis cycle. Because they absorb carbon dioxide, plants are described as greenhouse gas "sinks". Over many years, forests build up an important store of carbon in trees, soil and fallen leaves. When land is cleared, much of this is rapidly converted back to carbon dioxide by burning or decay.
Farming
Animals, particularly cattle and sheep, produce methane as food breaks down inside them. Some fertilisers release nitrous oxide. Rice production in paddy fields generates methane under water.
Waste breakdown
When organic material such as food scraps, garden wastes and paper are dumped in landfills, their decay creates carbon dioxide and methane. Sewage and wastewater treatment plants also release these gases as they break down wastes.
Industry
Many industrial processes create greenhouse gases. For example, cement and aluminium production involves chemical reactions that produce a variety of greenhouse gases.
BUT...we get help from the oceans and forests
The ocean absorbs carbon dioxide from the atmosphere. It also acts as a moderating influence on temperature ranges.
Forests also absorb carbon dioxide. Green plants use the energy of the sun and carbon dioxide from the air for photosynthesis; they create carbohydrates - the basis of the food chain on which almost all living things depend. Thus forests are a major store or bank of carbon, holding it in their trunks, roots, stems and leaves.
Greenhouse gases are a natural part of the atmosphere. It is the increase in the amounts of these gases through human activity that causes global warming. Human activity such as land clearing and burning fossil fuels have increased the concentration of these gases. Humans have had most impact on the enhanced greenhouse effect through increases in the amounts of carbon dioxide, methane and nitrous oxide.
Water vapour
Water vapour is the most important greenhouse gas, but human activity has little direct impact on the amount in the atmosphere.
Carbon dioxide (CO2)
The amount of carbon dioxide in the atmosphere is about 30% higher now than 200 years ago. The main causes of this increase are:
the burning of fossil fuels such as oil, coal and natural gas to create energy to make electricity and to produce fuel for transport, and
the clearing and burning of vegetation.
This gas is the biggest contributor to the enhanced greenhouse effect (about 70%)
Methane (CH4)
The amount of methane in the atmosphere is about 145% higher now than 200 years ago. The main causes of this increase are:
digestive processes of cattle and sheep (ie their burps!)
cultivation of rice
escape of natural gas
decomposing waste in garbage dumps or landfills.
This gas is the second biggest contributor to the enhanced greenhouse effect (about 20%)
Nitrous oxide (N2O)
The amount of nitrous oxide in the atmosphere is about 15% higher now than 200 years ago. The main causes of this increase are:
burning of vegetation
emissions from industries
the effects of agriculture on the soil (using nitrogenous fertilisers)
Halocarbons
These greenhouse gases have been reduced since the phasing out of chlorofluorocarbons (CFCs) to protect the ozone layer. However, other halocarbons effecting the atmosphere include perfluorocarbons (PFCs) emitted during aluminium production.
Fact sheet: Bad gas
How do we make greenhouse gases?
Burning fossil fuels
The burning of fossil fuels for energy (eg. for electricity and fuel for transport) generates the most greenhouse gases. When oil, gas, or coal burns, carbon in the fuel combines with oxygen from the air to form carbon dioxide. Methane is generated from coal mining and some natural gas pipelines.
Removing and burning vegetation
Growing plants absorb carbon dioxide from the air as part of their photosynthesis cycle. Because they absorb carbon dioxide, plants are described as greenhouse gas "sinks". Over many years, forests build up an important store of carbon in trees, soil and fallen leaves. When land is cleared, much of this is rapidly converted back to carbon dioxide by burning or decay.
Farming
Animals, particularly cattle and sheep, produce methane as food breaks down inside them. Some fertilisers release nitrous oxide. Rice production in paddy fields generates methane under water.
Waste breakdown
When organic material such as food scraps, garden wastes and paper are dumped in landfills, their decay creates carbon dioxide and methane. Sewage and wastewater treatment plants also release these gases as they break down wastes.
Industry
Many industrial processes create greenhouse gases. For example, cement and aluminium production involves chemical reactions that produce a variety of greenhouse gases.
BUT...we get help from the oceans and forests
The ocean absorbs carbon dioxide from the atmosphere. It also acts as a moderating influence on temperature ranges.
Forests also absorb carbon dioxide. Green plants use the energy of the sun and carbon dioxide from the air for photosynthesis; they create carbohydrates - the basis of the food chain on which almost all living things depend. Thus forests are a major store or bank of carbon, holding it in their trunks, roots, stems and leaves.
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