Intensified El Ninos in the Central Equatorial Pacific

According to authors Lee and McPhaden (2010), "satellite observations suggest that the intensity of El Niño events in the central-equatorial Pacific (CP) has almost doubled in the past three decades," citing the work of Cane et al. (1997) and Cravatte et al. (2009); and they say that this phenomenon "appears to be consistent with theoretically predicted change of the background sea surface temperature under global warming scenarios." To test this hypothesis, the authors used satellite observations of sea surface temperature (SST) over the past three decades "to examine SST in the CP region, distinguishing between the increases in El Niño intensity and changes in background SST."

In conducting their analysis, the two U.S. researchers discovered that the SSTs in the CP region during El Niño years are "getting significantly higher while those during La Niña and neutral years are not." Therefore, they reason that "the increasing intensity of El Niño events in the CP region is not simply the result of the well-documented background warming trend in the western-Pacific warm pool," but that "it is the increasing amplitude of El Niño events that causes a net warming trend of SST in the CP region."

Given these findings, Lee and McPhaden write that their results "suggest that, at least for the past three decades, the warming of the warm pool in the CP region is primarily because of more intense El Niño events in that region." In addition, they report that "in contrast to the CP region, the intensity of El Niño events in the EP region does not have a warming trend, and even has a cooling trend (though not significant at the 90% level of confidence) over the three-decade period." Thus, they say "further investigation is therefore needed to understand these issues better, given the uncertainty surrounding causal mechanisms and the implications the observed changes have for global climate and societal impacts."

Additional References
Cane, M.A., Clement, A.C., Kaplan, A., Kushnir, Y., Pozdnyakov, D., Seager, R., Zebiak, S.E. and Murtugudde, R. 1997. Twentieth-century sea surface temperature trends. Science 275: 957-960.

Cravatte, S., Delcroix, T., Zhang, D., McPhaden, M. and Leloup, J. 2009. Observed freshening and warming of the western Pacific warm pool. Climate Dynamics 33: 565-589.