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Recent reports of warming trends in the Red Sea raise concerns about the response of the basin's fragile ecosystem under an increasingly warming climate. Using a variety of available Sea Surface Temperature (SST) data sets, we investigate the evolution of Red Sea SST in relation to natural climate variability. Analysis of long-term SST data sets reveals a sequence of alternating positive and negative trends, with similar amplitudes and a periodicity of nearly 70years associated with the Atlantic Multidecadal Oscillation. High warming rates reported recently appear to be a combined effect of global warming and a positive phase of natural SST oscillations. Over the next decades, the SST trend in the Red Sea purely related to global warming is expected to be counteracted by the cooling Atlantic Multidecadal Oscillation phase. Regardless of the current positive trends, projections incorporating long-term natural oscillations suggest a possible decreasing effect on SST in the near future.

Plain Language Summary The recent warming trend of the Red Sea SST is critical for the fragile basin's ecosystem, especially for its precious coral reef community. Several studies based on satellite-era data sets recently reported warming rates that can rapidly alter the environmental status of the Red Sea in the near future. We show that the long-term variation of the SST over the Red Sea is influenced by a natural oscillation related to the Atlantic Multidecadal Oscillation. Satellite-era data sets coincide with a positive phase of this oscillation and the associated SST trend is overstated compared to the real, long term trend. As Atlantic Multidecadal Oscillation currently shifts from positive to negative phase, the Red Sea SST is expected to shift into a cooling phase during the next decades.