Are there long term trends associated with El Nino?
Yes. A number of climate indicators were noted to have changed in 1976, especially around the Pacific Basin. Prior to 1976, El Nino and La Nina occurred with about equal frequency, each at intervals of about 3-7 years. Since 1976, there have been 9 El Ninos (using a 6-month average of the Southern Oscillation Index of -0.50 as the criteria), or one every 2.2 years. There has been just one moderate La Nina in that interval (1988-89) and a rather weak La Nina (not even counted by some) in 1996-97. Longer perspectives, since 1860, indicate that the 1976-1997 period is quite unlike any other in the record. This is a source of considerable puzzlement at this time.
