Marine heatwaves – periods of unusually high sea surface temperatures – pose growing risks to both ecosystems and societies. Yet, until now, the atmospheric drivers behind these events in the Mediterranean Sea have remained uncertain.

A new study supported by ObsSea4Clim and published in Nature Geoscience sheds light on these mechanisms, revealing that persistent high-pressure systems, known as subtropical ridges, are the main trigger of Mediterranean summer marine heatwaves.

Giulia Bonino, Ronan McAdam, Panos Athanasiadis, and colleagues find that the subtropical ridges weaken the region’s prevailing winds, leading to a sharp reduction in evaporative cooling at the sea surface. In fact, the study highlights that reduced latent heat loss explains more than 70% of the heat trapped in affected areas, with additional warming amplified by increased short-wave radiation.

Using a multi-decadal macro-event dataset with cluster analysis, the researchers pinpointed the favourable atmospheric conditions that precede and intensify marine heatwaves. Their findings show that it is the combined effect between persistent ridges and weakened winds that creates the recipe for marine heatwaves in the Mediterranean.

This discovery marks a crucial step forward in predicting and simulating marine heatwaves. By identifying the specific atmospheric circulation patterns that lead to marine heatwaves, scientists can improve early-warning systems and help societies prepare for the environmental and economic challenges linked to a warming sea.

The full article is available here:

Bonino, G., McAdam, R., Athanasiadis, P. et al. Mediterranean summer marine heatwaves triggered by weaker winds under subtropical ridges. Nature Geoscience (2025). https://doi.org/10.1038/s41561-025-01762-9