25 March 2015

Understanding the El Nino-like Oceanic Response in the Tropical Pacific to Global Warming


After generations of climate assessment and climate model improvements, a picture is beginning to emerge about the tropical Pacific Ocean’s response to increasing greenhouse gases. Researchers, including a DOE scientist at Pacific Northwest National Laboratory, used a component of the Community Earth System Model (CESM), Parallel Ocean program version 2 (POP2) to investigate the sea surface temperature warming and the associated ocean processes of the central and eastern Pacific under global warming. They found that although the weakening of the equatorial easterlies increases the El Niño-like sea surface temperature (SST) warming, 80% can be simulated by the POP2 without considering the effects of wind change in both mechanical and thermodynamic fluxes. They found that wind stress change plays a dominant role in the tropical Pacific’s oceanic response below the surface, accounting for most of the changes in the equatorial ocean current system and thermal structures, including:

  • the weakening of the surface westward currents,

  • the increase of the near-surface stratification,

  • and the shoaling of the equatorial thermocline.

Interestingly, greenhouse gas warming in the absence of wind stress change and wind-evaporation-SST (WES) feedback also contributes substantially to the changes at the subsurface equatorial Pacific. Further, this warming impact can be largely replicated by an idealized ocean experiment forced by a uniform surface heat flux. This, arguably, reveals a purest form of the oceanic dynamical thermostat at work. 


This work is supported by National Natural Science Foundation of China (41376009 and 41221063) and NSF (AGS- 1249173 and AGS-1249145). Y. Luo would like to acknowledge the support from the Zhufeng and Taishan Projects of the Ocean University of China. J. Lu is supported by the Office of Science of the U.S. Department of Energy as part of Regional and Global Climate Modeling program. We wish to thank the anonymous reviewer for his/her helpful comments.