There really was quite a discussion on whether we had moved to more intense and frequent El Nino pattern post 1976.
Even a very cursory google search reveals much –
‘How will the El Niño phenomenon be affected by a global warming?
This is what the Dutch Meteorological Institute (KNMI) and the Max-Planck Institute (Germany), Matt Collins of Univ. Reading (U.K.) think. There is even a short entry about global warming and ENSO in Wikipedia. The brevity of this entry may reflect the fact that the question about how ENSO will respond to a global warming is still not settled. However, it seems that one common trait among some climate models is the indication that a global warming may result in a more a general El Niño-type average state (eg. Collins et al. 2005, Climate Dynamics, 24, 89-104. 19 and here).’ http://www.realclimate.org/index.php/archives/2006/05/el-nino-global-warming/
In reality there is little theory at all that explains varibility in ENSO – http://s1114.photobucket.com/albums/k538/Chief_Hydrologist/?action=view¤t=ENSO11000.gif