Li et al.  shed new light on the interwoven relationship between the diversity of El Niño events and the trending background state of the tropical Pacific. The authors use instrumental observations since the late nineteenth century to reveal a gradual cooling trend in the surface temperatures of the eastern equatorial Pacific Ocean. This trend is not a perfectly straight line—it tracks the undulations amid the general upward trend of global mean surface temperature very well. Whether an El Niño is centered in the central or eastern Pacific (a major aspect of ENSO diversity) is shown to be influenced by this slowly evolving background coolness of the eastern equatorial Pacific. The center of air-sea interaction is shifting westward away from the cooling waters, which suppresses the large-scale coupled feedback named after Jacob Bjerknes, resulting in more El Niño events peaking in the central Pacific.
Citation: Li, Y., Li, J., Zhang, W., Chen, Q., Feng, J., Zheng, F., … Zhou, X. (2017). Impacts of the Tropical Pacific Cold Tongue Mode on ENSO Diversity Under Global Warming. Journal of Geophysical Research: Oceans, 122. https://doi.org/10.1002/2017JC013052.
—Kristopher B. Karnauskas, Editor, JGR: Oceans