Future weakening of southeastern Tropical Atlantic Ocean interannual SST variability in a nested coupled model

Abstract

<p>Tropical Atlantic interannual sea surface temperature (SST) variability has significantly weakened since 2000. Here, we use a coupled ocean-atmosphere model with an embedded high-resolution nest in the tropical Atlantic Ocean to investigate future changes in the southeastern tropical Atlantic SST variability in response to anthropogenic global warming. In the model, the Angola-Benguela Area (ABA) is among the regions in the tropical Atlantic that exhibit the largest surface warming. Relative to 1970-1999, the SST variability in the ABA during the peak season, May-June-July (MJJ), decreases by about 24% during 2070-2099 under the worst-case scenario of the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5). The MJJ interannual temperature variability weakens along the Angolan and Namibian coasts in the top 40 m of the ocean. This reduction appears to be due to a smaller temperature response to thermocline-depth variations, i.e. a weaker thermocline feedback. The weaker thermocline feedback is found where the thermocline deepens the most. Our model results suggest that the trend towards a weakening of the interannual SST variability in the ABA observed during the recent decades could persist in the future under a worst-case global warming scenario.</p>

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“…projected to continue. A regionally refined global climate model indicates that coastal Angola Benguela SST variability will reduce by ~18% by the end of the century under the SSP585 scenario(Prigent et al 2022), while Atlantic Niño variability is projected to weaken by ~14% by the end of the century following RCP8.5 and SSP585 scenarios from the CMIP5 and CMIP6(Crespo et al 2022). The weakening of equatorial Atlantic SST variability has been linked to the warming of the upper ocean that reduces the influence of thermocline variability on SST(Crespo et al 2022), but also to the stabilization of the troposphere that reduces zonal wind variability.Despite continued improvements, the latest generation of climate models still exhibit large climatological warm SST biases in the eastern equatorial Atlantic, with too weak surface trade winds and a too deep thermocline.…”