The global increase in carbon dioxide concentrations are due primarily to fossil fuel use and land-use change.
Human activities are changing the climate
Greenhouse gas emissions from human activities are more than 90 per cent likely to have caused most of the global warming since the mid-20th century.
- 7 December 2009 | Updated 14 October 2011
- Greenhouse gases are a natural part of the atmosphere
- Atmospheric greenhouse gas exceeds pre-industrial levels
- Increased carbon dioxide causes ocean acidification
Greenhouse gases are a natural part of the atmosphere
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Greenhouse gases are a natural part of the atmosphere, trapping and re-radiating energy from the Earth’s surface.
The natural greenhouse effect maintains a surface temperature that can support life.
The main greenhouse gases are water vapour, carbon dioxide (CO2), methane, nitrous oxide, halocarbons and tropospheric ozone.
Greenhouse gas concentrations (excluding water vapour) often are expressed as a carbon dioxide equivalent (CO2-e).
Many other natural and human factors affect the climate.
Natural variability such as the El Niño cycle and variations in solar activity can affect the temperature, while large volcanic eruptions can lead to cooling.
Changes in land-use can either reduce or increase the amount of heat absorbed by the Earth’s surface.
Airborne particles (aerosols) have a net cooling effect.
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Fast facts
- Greenhouse gases are a natural part of the atmosphere, trapping and re-radiating energy from the Earth’s surface
- In the past 250 years, global CO2 concentration has risen 37 per cent, methane 150 per cent and nitrous oxide 18 per cent
- The increase in CO2 concentration is primarily due to fossil fuel use and land-use change, while increases in methane and nitrous oxide are primarily due to agriculture
- Greenhouse gas emissions from human activities are highly likely to have caused most of the global warming since the mid 20th century
