Sea surface temperature variability and drivers of marine heatwave trends in the Mediterranean Sea

The Mediterranean Sea is one of the most sensitive marine regions to climate change, with gradual warming and intensification of marine heatwaves (MHW) causing multiple environmental and socioeconomic damage. This study provides insights into sea surface temperature (SST) variability and explores the origin of MHW trends in the basin, using SST observations spanning 1982–2023. Results reveal a basin-wide increase in both mean and extreme SST, emphasized in the eastern basin. The Adriatic, Aegean and northern Levantine Seas exhibit the highest trends of SST as well as of extreme SST percentiles, identifying them as the most vulnerable Mediterranean areas. Beyond the underlying mean warming, parts of the western and central Mediterranean Sea show increased SST variability, whereas most of the eastern basin displays decreased SST variability. Our findings indicate a basin-wide dominance of mean warming over interannual variability in driving higher maximum MHW intensities, more extreme MHWs, longer heat exposure and greater accumulation of heat stress. However, interannual variability becomes the dominant driver of mean MHW intensity trends particularly in the western and central Mediterranean areas. Notably, mean MHW intensity is sensitive to the choice of the baseline climatology, suggesting a more complex nature of this metric compared to other MHW metrics. Future work should incorporate climate models, enabling a clearer distinction between the impact of anthropogenic forcing and the effect of natural variability on extreme SST events.