Palma: Warmer waters in the Mediterranean Sea may seem inviting for vacationers, but an intense ocean heatwave has sparked concerns among scientists about its potentially destructive impact on marine ecosystems. The sea surface temperature frequently exceeded 30°C off Majorca and other areas in late June and early July, reaching levels six to seven degrees above the norm.
According to BBC, these temperatures are comparable to those recommended for children's pools, which are typically kept between 29-31°C, or 30-32°C for infants, as per the Swimming Teachers Association. However, unlike swimming pools, the sea is not treated with cleaning chemicals, making it a breeding ground for harmful bacteria and algae in such warm conditions.
Sea temperatures of 30°C or above are occasionally observed in the Mediterranean in late summer, but this year's early occurrence is unusual. Data from the European Copernicus climate service, Mercator Ocean International, and Spanish port measurements indicate that the heatwave's early arrival suggests a more intense and prolonged summer. "We are all very, very surprised at the magnitude of this heatwave," noted Aida Alvera-Azcárate, an oceanographer at the University of Liege in Belgium.
Marine heatwaves are intensifying and lasting longer as greenhouse gases continue to warm the planet. Over the past 80 years, the frequency of extreme sea surface heat globally has tripled. Dr. Marcos from the University of the Balearic Islands in Spain explained that global warming is the primary cause, effectively transferring atmospheric heat to the ocean.
The Mediterranean, bounded by continents, is particularly vulnerable as it heats up rapidly under warm air, clear skies, and light winds. Karina von Schuckmann from Mercator Ocean International described the region as a "climate change hotspot." Although stronger winds in early July helped mix cooler waters with the warm surface, temperatures remain above average, posing potential unknown threats to marine life.
Marine organisms have a temperature threshold beyond which they cannot survive, and prolonged exposure to heat can deplete their energy reserves. "I remember four years ago diving in September at the end of summer; we found skeletons of many, many populations," recalled Emma Cebrian, an ecologist at the Centre for Advanced Studies of Blanes in Spain.
Seaweeds and seagrasses, which support diverse marine species and sequester carbon dioxide, struggle to withstand such extreme conditions. The heatwave can also lead to "sub-lethal effects," hindering reproduction in marine species. Dan Smale of the Marine Biological Association in Plymouth warned of possible repercussions on human societies, including fisheries losses, due to the early and severe temperature rise.
The Mediterranean's rapid warming serves as an indicator of climate change's impact on marine ecosystems. In addition to ecological effects, increased evaporation from warmer seas adds atmospheric moisture, potentially leading to extreme rainfall and flooding events, as witnessed in Libya in 2023 and Valencia in 2024. Coastal populations may also lose the cooling effect of sea breezes, exacerbating discomfort during future heatwaves, Dr. Marcos cautioned.