For that reason, the Med is “a climate change hotspot” said Karina von Schuckmann of Mercator Ocean International, a non-profit research organisation.
The heat peaked as June turned to July, after which stronger winds allowed deeper, cooler waters to mix with the warm surface above and bring temperatures down.
But temperatures remain above average and there could be consequences for marine life that we don’t yet know about.
Most life has a temperature threshold beyond which it can’t survive, though it varies a lot between species and individuals.
But sea creatures can also suffer from prolonged heat exposure, which essentially drains their energy through the summer to a point where they can no longer cope.
“I remember four years ago diving in September at the end of summer, we found skeletons of many, many, many populations,” said Emma Cebrian, an ecologist at the Centre for Advanced Studies of Blanes in Spain.
Seaweeds and seagrasses act a bit like the forests of the Mediterranean Sea, home to hundreds of species, as well as locking up planet-warming carbon dioxide.
“Some of them are well adapted to typical Mediterranean warm temperatures, but actually they often cannot withstand marine heatwave conditions, which are becoming more extreme and widespread,” said Dr Cebrian.