Abstract. In the context of a warming Mediterranean Sea, marine heatwaves (MHWs) have progressively intensified, leading to multiple environmental and socioeconomic damage. This study explores the origin of the observed trends in surface MHWs in the basin using sea surface temperature (SST) observations for the period 1982–2023. Results show a basin-wide increase in SST and extreme SST occurrences over the study period, emphasized in the eastern basin. The Adriatic, Aegean, and northern Levantine seas exhibit the highest trends in both SST and extreme SST percentiles, suggesting that these are the most vulnerable areas in the basin in terms of both accumulated warming and extreme SST occurrences. On top of the underlying mean warming, increased variability in SST is observed in parts of the western and central Mediterranean Sea, while decreased variability in SST is found in most of the eastern basin. Results reveal a basin-wide dominance of mean warming versus interannual variability in causing higher maximum MHW intensities, more extreme MHWs, longer heat exposure, and a greater accumulation of heat stress on an annual basis. Interannual variability becomes the dominant driver of the mean MHW intensity trends in most of the basin and particularly in the western and central Mediterranean areas. Mean MHW intensity is also differentiated from the other examined metrics due to the higher sensitivity of our trend attribution results for this metric to different methodological choices for climatological baselines, thus implying a more complex nature of this metric. To advance our understanding of forcing factors behind MHW trends in the Mediterranean Sea, future work should incorporate climate models that can explicitly represent the anthropogenic nature of trends against natural ocean variability.
Denaxa et al. (Tue,) studied this question.