ENSO Events Losing Their Intensity in a Warming Global Ocean

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The 2018-19 El Nino struggled to organize and intensify before dissipating the past couple months. Since the 1999 strong La Nina only 3 ENSO episodes have been intense. During this time the global oceans have warmed significantly. Is the warmer global ocean huring ENSO intensity?

Strength of ENSO Events Less Intense in Warmer Global Oceans

Fig. 1: Plot of NOAA/CPC seasonal operational ENSO index (ONI) identifying weaker character of ENSO events (both El Nino and La Nina) 1970-1999 versus 2000-2019.

Compared to the 100-year climatology global oceans have warmed from 0.39C warmer-than-normal in 1970-1999 to 0.73C warmer-than-normal in 2000-2019 (Fig. 1). The strength of ENSO episodes (both El Nino and La Nina) using the NOAA/CPC operational Nino index (ONI) indicates intensity (of ENSO events) has lowered during the past 20 years for each month of the year.

Proposed is ENSO events are weaker as the global oceans are warmer. The question arises due to the 2018-19 weak El Nino which struggled to organize and eventually fell apart during the past couple months. Since the strong 1998-2000 La Nina episode we’ve seen two strong La Nina events (2007-08 and 2010-11) and one strong El Nino (2015-16) whereas 12 strong ENSO episodes (7 La Nina and 5 El Nino) occurred 1970-1999.