The tropical climate response to GHG forcing is spatially non-uniform1,2,3. Even though enhanced equatorial and eastern Pacific warming is simulated by most climate models, the underlying mechanisms—including the relative roles of atmospheric and oceanic feedbacks—remain debated. Here, we use a climate model with idealized CO2-radiative forcing patterns to show that off-equatorial radiative forcing and corresponding coupled circulation/cloud adjustments are responsible for much of equatorial warming in response to global CO2 forcing. For equatorial forcing, the atmosphere responds by enhancing atmospheric heat export to the extra-tropics, an associated strengthening of the ascending Hadley circulation branch and strong negative equatorial cloud feedbacks. These processes together greatly dampen equatorial surface warming. Intensification of the oceanic subtropical cells and increased cold subsurface water upwelling in the eastern tropical Pacific provide an additional negative feedback for surface temperatures. In contrast, applying off-equatorial forcing, the atmosphere responds by exporting less heat from the tropics, Hadley circulation weakening and weaker negative equatorial cloud feedbacks, while the subtropical cells slow down in the ocean. Our results demonstrate a delicate balance in the coupled climate system between remote circulation adjustments and regional feedbacks that create the patterns of future climate change.
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The data from the regionally forced model simulations are available on the IBS Center for Climate Physics climate data server (https://climatedata.ibs.re.kr/).
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M.F.S., A.T., K.-S.Y., J.-E.C. and E.-S.C. were supported by the Institute for Basic Science (project code IBS-R028-D1). F.-F.J. was supported by NSF grant no. AGS?1813611 and DOE grant no. DE-SC0005110. C.M.B. was supported by NOAA grant no. CPO NA115OAR4310161. C.P. was supported by a JISAO postdoctoral fellowship. K.C.A. was supported by NSF grant no. AGS-1752796. S.M.K. and D.K. were supported by Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning (grant no. 2016R1A1A3A04005520). M.H. was supported by JSPS Overseas Research Fellowships (no. 201860671). Computing resources were provided by University of Southern California’s Center for High-Performance Computing. M.F.S. thanks S.-P. Xie and A. N. Babu for valuable discussions.
The authors declare no competing interests.
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Stuecker, M.F., Timmermann, A., Jin, FF. et al. Strong remote control of future equatorial warming by off-equatorial forcing. Nat. Clim. Chang. 10, 124–129 (2020). https://doi.org/10.1038/s41558-019-0667-6
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