Increased Shortwave Radiation Dampens Summertime SST Tendency in Mid‐Latitude Oceans Under Future Warming Scenarios

Abstract Shortwave radiation penetrating through the bottom of the mixed layer (ML) ( Q pen ) significantly modulates sea surface temperature (SST) variability. Here, we show that summertime Q pen is projected to increase by 3.9 (3.7) ± 1.9 (1.6) W m −2 in the northern (southern) mid‐latitude oceans under the high emission scenario (SSP5‐8.5) during 2051–2100 compared to the historical simulation during 1951–2000. This increase is driven primarily by a ML shoaling, and secondarily by a reduction of chlorophyll in summer. The latter exerts a pronounced impact on Q pen , resulting from higher sensitivity of Q pen to seasonal chlorophyll reduction in mid‐latitude oceans due to the shoaling of the summertime ML. Furthermore, the enhanced Q pen reduces the magnitude of SST tendency by 25.3% in summer, thereby weakening summertime month‐to‐month SST tendency in these regions. These results highlight the critical role played by Q pen in ocean warming, requiring a better representation of radiation penetration in climate models.