A formidable marine heatwave has gripped the western Mediterranean since late June, alarming marine scientists and environmentalists due to its intensity, timing and potential for long-lasting ecological damage. With sea surface temperatures soaring above 30 °C—sometimes reaching as much as 5 °C above the region’s 20-year average—this heat event is far more extreme and earlier than typically expected.
Since late June, regions around Mallorca and Portugal’s southern Algarve have experienced sustained sea temperatures typically seen in high summer, not early summer. The Portuguese maritime authority logged the marine heatwave from 28 June to 9 July. In portions of the western Mediterranean, water has consistently registered temperatures 5 to 6 °C above the norm—levels usually associated with peak mid-summer, not June.
Meteorologists attribute this alarming phenomenon to a persistent “heat dome”—a high-pressure system that traps warm air over the region. Coupled with clear skies and light winds, this dome has caused the surface waters to heat rapidly and remain at elevated temperatures without cooling through mixing or storms.
Marine heatwaves of this severity carry heavy ecological consequences. Extended exposure to elevated temperatures can strip marine organisms of energy and impair reproduction. When water exceeds 30 °C, its habitability for certain species can collapse rapidly, disrupting breeding, migration and food chains.
Historical precedents paint a dire picture: major Mediterranean heatwaves in 2015–2019 triggered massive die-offs of seagrass, kelp beds and coral systems. This year’s anomaly mirrors those worst-case events, and could spell a repeat or intensification of those ecological catastrophes.
Such losses extend beyond biodiversity: seagrass meadows and kelp forests are natural carbon sinks and essential buffers against coastal erosion. Their depletion compromises fish nurseries and diminishes natural defences against storms and rising seas.
Warm sea surfaces are not only local threats—they also influence atmospheric patterns. Hotter waters boost evaporation, increasing local humidity and dew points. This moisture can feed into more powerful storm systems in late summer and autumn, raising the risk of extreme rainfall and flash flooding. Past events—such as the catastrophic flooding in Slovenia in August 2023—have been exacerbated by abnormally warm Mediterranean waters.
The heatwave also feeds into a broader pattern of escalating marine heat events globally. Research shows that, since the 1940s, marine heatwave days have nearly tripled—from around 15 days annually to almost 50—driven largely by human-caused warming due to fossil fuel emissions. The Mediterranean has been a hotspot, where local spikes of up to 5 °C above average now occur more often.
Record-breaking marine temperatures in late June and early July represent the western Mediterranean’s most extreme heat event for that time of year. Without a shift in weather patterns, models predict the heat dome—and thus elevated sea temperatures—may persist well into July.
Experts are closely monitoring changes in seawater, marine ecosystems, and weather forecasts to anticipate emerging fisheries disruptions, bleaching events, or toxic algal blooms.
This early-season heatwave is not just an anomaly—it signals a shifting baseline in marine climatology. Scientists warn that dramatic warming could become the norm if greenhouse gas emissions continue unabated. With higher sea temperatures linked to more deadly storms and heat-related disasters, cutting fossil fuel usage remains the only viable long-term solution.
In the meantime, urgent research, conservation efforts, and marine protections are essential to support ecosystems under stress. Marine managers are urged to adapt fishing quotas, create resilient marine protected areas, and bolster monitoring systems to react to this evolving—and intensifying—challenge.
