Thanks Andre,

There is no doubt that more triple La Nina's have happened in the past. Though due to the lack of observations in the Pacific prior to 1950, there are bound to be larger error bars on any attempt to determine sea surface temperature anomalies in the Nino3.4 region.

That's why we only go back to 1950 with confidence.

Either way, this just illustrates the variability that exists within ENSO.