Fig. 2: Mechanism linking initial and future ENSO variability through ENSO nonlinear thermal damping. | Nature

Fig. 2: Mechanism linking initial and future ENSO variability through ENSO nonlinear thermal damping.

From: Addendum: Butterfly effect and a self-modulating El Niño response to global warming

Fig. 2

The results from the CESM-LE experiments. a, Relationship between the monthly SST in which the E-index peaks (2° S–2°N,100°W–110°W) and net heat flux over the eastern Pacific (EP, 5°S–5° N, 150° W–90° W). b, Interexperiment relationship between the eastern Pacific SST variability (1920–1969) and cumulative ocean heat loss (at 0°, 105° W, indicated by a black cross in c). The blue stars and orange diamonds represent the ten experiments with the weakest and strongest initial eastern Pacific SST variability (°C), respectively. Solid black circles represent other experiments. c, Interexperiment regression of 40 cumulative heat flux fields onto 40 values of SST variability (°C) in which the E-index peaks (2° S–2° N, 100° W–110° W) over the initial 50 years (1920–1969), showing an ENSO pattern of cumulative heat flux. Statistical significance above the 90% and 95% confidence levels based on a two-tailed Student’s t-test is indicated as black stippling and green solid contours, respectively. d, Difference in linear trends of mean ocean temperature of the equatorial Pacific (average over 5° S–5° N) over the first 150 years, between the average of ten experiments with strongest and weakest initial SST variability (°C), indicating eventual cooling of the eastern equatorial Pacific. The anomalous cooling, stemming from cumulative heat loss generated since the initial period of strong ENSO variability, weakens greenhouse-warming-induced enhancement of stratification in the upper equatorial Pacific, and leads to a smaller increase in ocean-atmosphere coupling and thus a weaker future increase in ENSO variability.

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