What is climate change?
Climate is usually defined as the 'average weather' or, more rigorously, as a statistical description of the mean and variability in the weather over a period of time. Therefore, climate change refers to a statistically significant change in either the average weather, or its variability over a period of time.
Climate change is the most pressing environmental issue facing us today.
In 2007, the Intergovernmental Panel on Climate Change (IPCC) in its Fourth Assessment Report (AR4) concluded that it is very likely (more than 90 per cent probability) that most of the warming in the past 50 years is due to the observed increase in greenhouse gas concentrations, which has amplified the greenhouse effect.
An idealised model of the natural greenhouse effect. (Source IPCC AR4 Working Group 1 2007)
The greenhouse effect is ordinarily a natural process that traps heat in the atmosphere to create climatic conditions in which humans, plants and animals live. Evidence has shown that human activities, such as the burning of fossil fuels, increase the concentration of greenhouse gases including carbon dioxide, methane and nitrous oxide in the atmosphere. This is known as the 'enhanced greenhouse effect', which causes more heat to be trapped in the atmosphere, resulting in global temperature rises, a rise in sea-levels and melting of mountain glaciers and sea-ice.
For further information
- on the impacts of greenhouse gases on the climate see The Bureau of Meteorology publication The Greenhouse Effect and Climate Change (PDF)*
- on the indicators used to measure the temperature of the world see NASA’s Eyes on the Earth and the National Oceanic and Atmospheric Administration publication The State of Climate (PDF)*
- on some of the commonly used terms around climate change see the downloads and links section of this website.
* Requires Adobe Reader
Last updated 6 September 2011