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.

In 2007, the Intergovernmental Panel on Climate Change in its Fourth Assessment Report 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.

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-level and melting of mountain glaciers and sea-ice. 

Climate change is the most pressing environmental issue facing humanity today.

The Downloads section of this website includes a fact sheet that explains some of the commonly used terms around climate change.