This combined atmospheric-oceanic phenomenon, usually occurring around every two to seven years, is known as the El Nino-Southern Oscillation (ENSO). Many weather and climate extremes are the result of natural climate variability (including phenomena such as ENSO), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur.