English: This image shows three examples of internal climate variability between 1950 and 2012: the El Niño–Southern oscillation, the Arctic oscillation, and the North Atlantic oscillation (see the Intergovernmental Panel on Climate Change (IPCC, 2001) for a definition of "internal" climate variability). The El Niño – Southern Oscillation (ENSO) is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean (NOAA Climate Program Office, 2009a). The Arctic Oscillation (AO) refers to an atmospheric circulation pattern over the mid-to-high latitudes of the Northern Hemisphere (NOAA Climate Program Office, 2009b). The North Atlantic Oscillation (or NAO) is a prominent pattern of climate variability that has a strong influence on weather over north-eastern North America, Greenland, and Europe (NOAA Climate Program Office, 2009c). The top graph shows the ENSO, the middle graph the AO, and the bottom graph the NAO.

In the top graph, the ENSO cycle is measured using the Oceanic Niño Index or ONI (for details, see NOAA Climate Program Office, 2009a). In the middle graph, the AO is measured using the Arctic Oscillation Index (for details, see NOAA Climate Program Office, 2009b). In the bottom graph, the NAO is measured using the North Atlantic Oscillation Index (for details, see NOAA Climate Program Office, 2009c).

References: IPCC, 2001: Appendix I - Glossary: Climate variability, in: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the IPCC Third Assessment Report (J.T. Houghton, et al., (eds)). Cambridge University Press; NOAA Climate Program Office, August 30, 2009a: ClimateWatch Magazine » Climate Variability: Oceanic Niño Index. NOAA; NOAA Climate Program Office, August 30, 2009b: ClimateWatch Magazine » Climate Variability: Arctic Oscillation. NOAA; NOAA Climate Program Office, August 30, 2009c: ClimateWatch Magazine » Climate Variability: North Atlantic Oscillation. NOAA.