ENSO diversity throughout the Last Millennium: insights from PMIP simulations

The El Niño-Southern Oscillation (ENSO) is the largest source of interannual climate variability, and occurs through two flavors: Canonical and Modoki events. Canonical events are characterized by warm sea surface temperature anomalies (SSTAs) over the eastern tropical Pacific, while these SSTAs are weaker and displaced to the central Pacific during the Modoki events. Previous research has addressed ENSO variability and diversity during the recent past and its projected changes due to climate change, but few studies have focused on ENSO behavior, during the Last Millennium (LM). This paper assesses changes in ENSO diversity throughout the LM using simulations from six models included in the third and fourth phases of the Paleoclimate Model Intercomparison Project. Although the simulated warming/cooling patterns are comparable to the reference data set over the historical period, they fail to correctly simulate the SSTA diversity between both types of La Niña prior to the historical period. Also, while the models resemble the ENSO atmospheric circulation and teleconnection patterns, they fail in reproducing their associated precipitation anomalies, particularly in continental regions. Finally, models suggest an increase in ENSO frequency during the historical period with respect to the LM, particularly for Canonical El Niño and La Niña Modoki flavors.