On 13 August, the surface waters of the Mediterranean Sea reached an average temperature of 28.54°C, the highest daily figure since comparable records began in 1940, according to Spain's State Meteorological Agency (Aemet). The agency noted on social media that throughout almost the entire month of August, the sea has been breaking daily temperature records one after another, with little respite.
The announcement comes just weeks after Mercator Ocean International, which operates the Copernicus marine service, confirmed that July was the hottest month ever recorded in the Mediterranean. That month's average was 27.07°C, with a margin of uncertainty of ±0.27°C, surpassing the previous record of 26.68°C set in July 2025 by four-tenths of a degree. Mercator's comparison series starts in 1993, so both agencies, despite using different methodologies and reference periods, agree that the sea has entered a thermal regime never seen before.
A pattern that has been building for months
This trend was already evident in late June. Aemet warned then that Mediterranean temperatures had reached levels typical of the second half of August, when the sea is usually at its warmest. At the start of the summer, temperatures rose to 2.6°C above normal, with the sea exceeding the average normally seen in mid-August while it was still June—an anomaly the agency described as exceptional.
The phenomenon is not confined to the Mediterranean. Globally, July 2026 was the month with the highest ocean surface temperature ever recorded, with an average of 21°C between 60° north and 60° south. Across the Mediterranean basin, 27% of the sea experienced its warmest July since 1993, and around 70% of the surface ranked among the four hottest Julys ever measured, ruling out the idea that the record is due to a few exceptional locations.
It is important to stress that the sea-temperature record cannot be singled out as the direct cause of high temperatures on land, as many different factors come into play in the atmosphere. However, it can alter conditions along the coast. Water releases heat more slowly than land, so a warmer Mediterranean makes it harder for temperatures to fall at night, increases humidity, and leads to hotter nights near the shore.
The build-up of energy in the sea also affects ecosystems. Prolonged marine heatwaves subject organisms adapted to specific thermal ranges to considerable stress, potentially altering species distribution, increasing mortality, and changing the functioning of entire coastal communities. This is part of a broader pattern of accelerating climate shifts in the Mediterranean.
With the figure recorded on 13 August, the Mediterranean has again surpassed the record it had set only a few weeks earlier, in a summer that, on land and at sea, keeps breaking its own records. The heat has also contributed to elevated flash-flood risk across southern Europe as the season transitions. Meanwhile, Spain has already recorded a record number of heat-related deaths this year, underscoring the human toll of these extreme conditions.
