Lorraine Williamson
Spanish scientists have warned that marine heatwaves in the Mediterranean are becoming more frequent, intense, and longer-lasting.
Research from IMEDEA, a Spanish marine and climate research institute, highlights a significant shift in sea temperature patterns, with serious implications for Spain’s coastal ecosystems and economies.
Rising temperatures in the Mediterranean
In the 1940s, marine heatwaves in the Mediterranean lasted around 15 days per year. Today, they persist for close to 50 days annually. These prolonged periods of elevated sea temperatures are especially pronounced in the western Mediterranean, notably around the Balearic Islands and Spain’s eastern seaboard, where temperatures have exceeded the seasonal norm by more than five degrees Celsius.
Marine heatwaves are periods when sea temperatures remain unusually high for at least five consecutive days. While they may go unnoticed on the surface, their impact beneath the waves is considerable.
“If we look at the summer of 2023, the data show the exceptionally hot summers experienced between 2021 and 2023, with increases of more than 2°C each year, attributable to global warming,” says Dr. Marta Marcos, an oceanographer at the University of the Balearic Islands. “We have also observed this same role of global warming in generating marine heatwaves in episodes that occurred at other times and in other parts of the world, such as the northeast Pacific heatwave between 2014 and 2015 or the heatwave that affected the Tasman Sea between 2015 and 2016,” adds Marcos.
Environmental and economic effects in Spain
Spain is already experiencing the consequences. Seagrass meadows such as Posidonia oceanica, crucial for biodiversity and CO₂ absorption, are under serious threat in Balearic waters. As these habitats decline, so too does the balance of the marine ecosystem.
Disruptions in marine food chains have also been recorded. Warmer seas are causing native fish species to decline while invasive species spread, impacting both biodiversity and the fishing industry. Coastal communities that rely on fishing and tourism face growing uncertainty as the natural marine environment changes.
Ripple effects on weather and communities
Warmer sea temperatures also influence weather on land. Heavier rainfall and more frequent flooding have been linked to warming seas, increasing the risk of damage to infrastructure and communities along Spain’s Mediterranean coast.
Monitoring and understanding the change
In response to these challenges, researchers from the Spanish Institute of Oceanography (IEO) are actively collecting data across the Mediterranean. Their studies examine sea temperature, salinity, oxygen levels, and plankton populations — all essential indicators of ocean health.
These findings support a growing consensus among marine scientists that climate change, driven by human emissions, is directly contributing to more frequent marine heatwaves. Marcos and her colleagues argue that nearly half of all extreme marine heatwaves recorded since 2000 would not have occurred without the effects of global warming.
A call for urgent global action
Experts agree that marine heatwaves will become increasingly common unless urgent action is taken to cut greenhouse gas emissions. Spanish researchers are urging the international community to step up efforts to mitigate climate change, warning that delays will lead to long-term ecological and economic damage.
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