Climate change has dramatically intensified this summer’s exceptionally high sea temperatures around Europe, adding about 2C of warming in parts of the Mediterranean and greatly expanding the area affected by marine heatwaves, according to new research.
Scientists from the World Weather Attribution (WWA) group said on Wednesday that human-caused global warming was the main factor behind unusually warm conditions stretching from the seas around Ireland and western Britain to the Atlantic off the Iberian Peninsula and across the Mediterranean.
‘This summer, we’ve seen some really exceptional ocean temperatures around Europe,’ said Catherine Gregory, a climate scientist at the University of Bern who contributed to the study.
‘By July, the average temperature of the entire Mediterranean Sea was just over 27C, which was the highest July value on record,’ she added. ‘We’ve had a buoy reading to the west of Mallorca measuring more than 33C in open water … and we’ve seen similarly extreme conditions in the North Atlantic.’
The findings come after a summer in which large areas of Europe have also experienced severe heatwaves, drought and wildfires, with scientists warning that rising temperatures on land and at sea are increasingly linked to the continued accumulation of greenhouse gases in the atmosphere. ALSO READ: Studies says climate change dramatically increased likelihood of devastating Spain and France wildfires.
According to the European Union’s Copernicus Climate Change Service, global ocean temperatures reached record levels for a second consecutive month in July.
In some areas of the Mediterranean, sea surface temperatures were more than 6C above normal during the hottest two weeks of July.
For its analysis, the WWA examined four regions: the Western Mediterranean, Eastern Mediterranean, the Atlantic around the Bay of Biscay and Iberian Peninsula, and waters surrounding Ireland and western Britain. Researchers combined observational records with climate model simulations to compare this year’s conditions with those expected in a world without human-caused climate change.
‘We find it’s the most extreme July marine heat wave conditions in the record for the Western Mediterranean, the Celtic region, and for the Bay of Biscay-Iberian Peninsula region,’ said Gregory.
The researchers estimated that climate change raised sea temperatures by about 2C in both the Eastern and Western Mediterranean. Its contribution was calculated at around 1.4C in the Bay of Biscay and waters off the Iberian Peninsula, and approximately 1.3C around Ireland and western Britain.
‘From the Atlantic waters off Ireland to the Mediterranean Sea, Europe’s seas are experiencing an alarming surge in temperatures,’ said co-author Thomas Frolicher, an environmental physicist at the University of Bern, Switzerland.
‘Our research shows clearly that this is being driven by climate change, in particular by the continued burning of fossil fuels,’ he added.
The study found that global warming has not only increased temperatures but substantially enlarged the geographical extent of marine heatwaves.
Around 90% of the Bay of Biscay and Iberian coast region has experienced marine heatwave conditions this year, compared with an estimated 40% in a climate without the approximately 1.4C of human-caused global warming already experienced.
In the Western Mediterranean, about 80% of the region has been affected, rather than the estimated 40% without climate change.
The contrast was even greater in the Eastern Mediterranean, where marine heatwaves have affected around 70% of the sea this year. Researchers estimated that without human-caused warming the figure would have been only about 9%.
Around Ireland and western Britain, approximately 80% of the area has experienced marine heatwave conditions, compared with an estimated 30% in a world without climate change.
The consequences extend well beyond unusually warm water for swimmers. Oceans absorb most of the excess heat generated by rising greenhouse gas concentrations, and sustained increases in sea temperatures can profoundly alter marine ecosystems.
The WWA said there was ‘evidence of severe ecological impacts’, with species ‘shifting northwards to cooler waters, disrupting food chains, coastal fisheries and aquaculture’.
Species capable of moving can migrate towards cooler waters, while organisms such as corals and seagrasses are much less able to escape prolonged periods of extreme heat and can suffer widespread die-offs.
The changes do not affect all marine species in the same way. Some organisms that favour warmer conditions can flourish, particularly if competitors or predators are weakened or disappear.
‘We have what we call winners and losers. So a lot of species wane in abundance or completely disappear while others bloom and proliferate,’ said marine ecologist John Bruno, one of the study’s co-authors.
The result can be a major restructuring of marine ecosystems, with knock-on consequences for fishing, aquaculture and coastal economies. Warmer conditions can also favour species such as jellyfish, while other marine animals increasingly move into areas where they were previously uncommon.
Researchers warned that the effects of exceptionally warm seas can also extend onto land.
‘Impacts can spill into land too, with higher sea surface temperatures driving up humidity for coastal areas increasing the risks of extreme heat,’ the WWA said.
Warm seas can supply additional heat and moisture to the atmosphere, worsening the combination of high temperatures and humidity experienced by people living near the coast. They can also provide more energy and moisture for storms and extreme rainfall when the necessary atmospheric conditions develop.
‘We find that when we have very warm sea surface temperatures, they provide added energy to storms,’ said Gregory. ‘And then we also have the added impact of additional stress during land heat waves as well.’
Scientists have previously highlighted the role that unusually warm Mediterranean waters can play in providing moisture for intense rainfall events, including the conditions associated with the catastrophic flooding in Valencia in 2024. Click here for all our reports related to the Valencia Floods.
The findings underline the contrast between the apparent attraction of warmer European seas for tourists and the potentially serious consequences beneath the surface.
Claire Bergin, a study co-author and researcher at Maynooth University in Ireland, said that ‘warmer waters for swimming may sound appealing to beachgoers in cooler countries like mine’.
However, ‘the impacts on marine life beneath the surface are more serious’.
Click here to download the full report from the World Weather Attribution (WWA).
ALSO READ: PP and Vox reject Sánchez’s national climate pact as prime minister defends government’s record.
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