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20th-Century ENSO Events
Mendelssohn, R., Bograd, S.J., Schwing, F.B. and Palacios, D.M.  2005.  Teaching old indices new tricks: A state-space analysis of El Niņo related climate indices.  Geophysical Research Letters 32: L07709, doi:10.1029/2005GL022350.

What was done
Climate-alarmists often claim that global warming will increase both the frequency and intensity of ENSO events; and they use this claim in an attempt to convince the general public that continued burning of fossil fuels, which they claim is the major cause of the past century's rise in temperature, will lead to disastrous climatic consequences.  In the present study, Mendelssohn et al. investigate these claims by performing a statistical analysis known as state-space decomposition on three El Niņo-related indices (Southern Oscillation Index, its component sea level pressure series, and the NINO3 index) during the 20th century.

What was learned
The stochastic cycles produced by the state-space models were all relatively stationary, which, in the words of the investigative scientists, does "not support the idea that El Niņos have become more frequent."  With respect to the magnitude of ENSO events, they say there were some "outlier events" in the later portion of the record, which may suggest that ENSO magnitudes have increased in recent years, but they conclude that "it is premature to tell."

What it means
In contrast to long-standing climate-alarmist claims, ENSO events do not appear to have become more frequent over the 20th century.  With respect to their magnitudes, however, the situation is less clear, and we will probably have to wait several more cycles before a definitive answer can be obtained from statistical state-space decomposition analysis.  In the mean time, we invite you to examine the many other studies we have reviewed on this topic in our Subject Index (see ENSO - Relationship to Global Warming), which clearly suggest there is nothing unique or unprecedented about ENSO events of the past century.

Reviewed 27 July 2005