Natural Climate Variability

Climate varies on all time scales, from one year to the next, as well as from one decade, century or millennium to the next. The complex nature of this variability is a major obstacle to the reliable identification of global changes brought about – in the past, present or future – by the presence and activities of humanity on this planet. This article discusses observed climate variability on various time scales, paleoclimatic, interdecadal to centennial, seasonal to interannual, and intraseasonal. Key ideas to explain the observed variability are presented, and some of the models used to explore these ideas are mentioned. Finally, we discuss briefly the implications of these ideas for the detection and prediction of climate change.