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What is climate change?

The climate is ‘a complex, interactive system consisting of the atmosphere, land surface, snow and ice, oceans and other bodies of water, and living things.’ [see reference 1] A range of factors may influence the balance of the climate system including both natural and anthropogenic factors. Climate is often described in regard to the average and variability of temperature, precipitation and wind over a period of time (eg 30 years); [see reference 1] or more simply, climate may be defined as ‘average weather’.

There are varying definitions and interpretations of climate change (see Box 1).

Box 1: Definitions of climate change The Intergovernmental Panel on Climate Change (IPCC) defines climate change as ‘any change in climate over time, whether due to natural variability or as a result of human activity'. [see reference 2] The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as ‘a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over comparable time periods’. [see reference 3] The World Meteorological Organisation (WMO) defines climate change as ‘a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use’. [see reference 4]

These definitions differ in relation to the contribution of natural variation versus anthropogenic factors. The IPCC and WMO definitions take into account both natural climate variability and anthropogenic alterations in climate, while the UNFCCC definition places natural climate variability outside of their definition.

The term climate change is often incorrectly conflated with other terms, for example ozone depletion or air pollution. Misinterpretation and confusion over the differences between global warming, climate change and processes such as the greenhouse effect are also common. For a glossary of terms please see the IPCC glossary at www.ipcc.ch/glossary/index.htm.