Assessment of Red Sea temperatures in CMIP5 models for present and future climate

depths will contribute to enhance the vertical stratification. The absolute value of the stratifica- tion is not available as the density fields were not available for all the models used in this study. However, the reported differential warming would contribute to increase the density differ- ence between surface and 300m in 0.38 kg/m3. Scenario RCP4.5 projects more vertically homogeneous warming, with projected anomalies of approximately 1.5˚C at all levels of the upper 300 m for the period (2080–2100). Under RCP4.5, thus, it is not expected that warming would induce changes in the stratification. The spread of model projections is almost constant through the water column, with an ensemble STD of 0.9˚C and 0.4˚C under RCP8.5 and RCP4.5, respectively. All models project the same behaviour in terms of the shape of the anom- aly profiles under both scenarios, which provides an estimate of the robustness of the results, with enhanced stratification under scenario RCP8.5 and homogeneous warming under sce- nario RCP4.5 (S4 Fig). Impact of mean temperature rise on marine heat waves The future evolution of marine heat waves depends on two factors. On the one hand it depends on changes in the mean temperature, and on the other hand on changes in the intra-seasonal variability. In terms of the probability density function (pdf), the first would imply a shift in the pdf location, while the second would imply a change in the shape of the pdf. The first factor is usually the dominant one, accounting for a large part of the projected changes in MHWs

(e.g. in the Mediterranean the changes in the mean temperature account for more than 80% of the projected changes in the maximum temperature), [18,22]. Unfortunately, high frequency Fig 9. Historical (grey) and future projection of the Red Sea SST basin average (in ˚C) under scenario RCP 8.5 (red) and scenario RCP4.5 (blue). The solid lines indicate the ensemble average while the patch represents the range of values from the ensemble. Yellow lines indicates a linear trend fitted for both scenarios for the period 2006–2050 (solid lines) and 2051–2100 (dashed lines). The vertical boxes indicate the time period when the global temperature would be 1.5˚C above preindustrial levels in both scenarios. https://doi.org/10.1371/journal.pone.0255505.g009 PLOS ONE Assessment of Red Sea temperatures in CMIP5 models for present and future climate PLOS ONE | https://doi.org/10.1371/journal.pone.0255505 July 30, 2021 15 / 26