The western Mediterranean and parts of the north-eastern Atlantic have experienced marine heatwave conditions during the summer, with unusually warm waters affecting large areas.

Data from Copernicus showed some of the largest differences at the end of June in the western Mediterranean. In the Gulf of Lion, off southern France, and in parts of the sea west of Italy, surface temperatures were around 6°C above the long-term average.

The unusually warm conditions have continued through the summer. The Mediterranean as a whole averaged around 27°C in July, the highest July temperature on record for the sea, Reuters reports. In early August, a buoy near Mallorca recorded water temperatures of around 33°C.

Scientists say human-caused climate change is the main factor behind the exceptionally high sea temperatures. Research cited by Reuters estimates that climate change added around 2°C to temperatures in the Mediterranean and around 1.4°C in western European seas.

Portugal has also experienced unusually warm ocean temperatures this summer. In July, Atlantic waters off the Algarve reached 26.1°C, with two marine heatwave episodes recorded off Faro.

The warmer water is not only noticeable for people swimming in the sea. Long periods of unusually high ocean temperatures can put marine ecosystems under considerable pressure, affecting fish and other species and potentially causing deaths among organisms unable to adapt or move to cooler waters.

Unusually warm seas can also influence weather on land, providing more moisture that can contribute to heavy rainfall.

Copernicus has been monitoring unusually high sea temperatures around Europe for several months. Marine heatwave conditions were already present in parts of European waters towards the end of May, before further warming was recorded during June and the summer months.