Just days before the official start of summer, the oceans and seas surrounding Spain are experiencing unusually high temperatures, reaching “historic highs” in some areas. Of particular concern is Valencia, where the port’s buoy recorded a sea temperature of 25.57 degrees Celsius last Saturday (June 14, 2025). This figure was only reached on July 9 last year, and the highest June temperature in 2024 was 24.5 degrees at the end of the month.
Why Sea Water Is Warming So Fast: Experts Explain the Causes
This dramatic temperature increase is not an isolated incident but part of a broader phenomenon. José Ángel Núñez, spokesperson for the state meteorological agency Aemet, explains that there is a constant exchange of heat in systems like the sea and the atmosphere. In the Mediterranean, a relatively small and enclosed basin, the rapid warming of the air quickly leads to an increase in sea temperature.
“Furthermore, heat does not only affect the surface: it accumulates and spreads deep,” says Núñez. “This means that thermal peaks arrive earlier each summer with increasingly extreme values, thus surpassing previous records.”
A Quarter of the Year Already “Historically Warm” in the Balearics
The Aemet expert further elaborates that in the waters of the Balearic Islands – with data up to June 4 – 35 of the past 155 days have already exceeded the historical temperature record for the corresponding day. This means that almost a quarter of 2025 in this region can already be classified as “historically exceptionally warm.”
The Record Flood of Sea Temperatures in Spain
The maximum temperature records in all Spanish sea areas between 1940-2024 were reached between 2022 and 2023. In contrast, the lowest values in the Mediterranean were recorded between 1940 and 1941, and in the Atlantic Ocean in 1972.
Western Mediterranean: The Hotspot of Temperature Increase
The western Mediterranean is particularly affected by the temperature increase, especially the maritime area of the Balearic Islands. This includes the waters between Mallorca, Menorca, Valencia, Castellón, Tarragona, and Barcelona. “In these areas, the increase was 1.3 degrees Celsius, which is more than double that in Finisterre and almost double that in the Canary Islands,” Núñez emphasizes.
Last year, the water temperature record off the coast of Valencia was measured on August 10 at 7:00 PM when the water reached 29 degrees.
Increased Evaporation: A Direct Consequence of Ocean Warming
The warming of air and sea in recent decades is closely linked to changes in various components of the water cycle and hydrological systems. A significant consequence is the increase in evaporation and water vapor content in the atmosphere.
Núñez clarifies that in line with the observed warming – which is more pronounced in the summer months for both sea and air temperatures – there has been a significant increase in evaporation in summer, and a large part of this moisture flow from the surface into the atmosphere leads to a remarkable increase in the total water in the atmospheric column over the western Mediterranean.
This situation means not only greater energy availability but also an increase in humidity, factors that, when combined with the appropriate atmospheric configuration, favor the occurrence of more intense and torrential weather phenomena, the spokesperson concludes.
The 29-Degree Threshold: A New Normal?
Until 2022, the highest value on the Valencian coast was 28.65 ºC, measured on August 7, 2015. However, since 2022, the 29 ºC threshold has been reached or exceeded up to three times in a row:
- 2022: Reached 30 ºC (exactly 29.94 ºC) on August 11.
- 2023: The 29 degrees (exactly 29.48 ºC) were exceeded on August 24.
- 2024: The maximum temperature on August 10 was 29 degrees.
Neither in 2023 nor in 2024 were water temperatures above 25 degrees measured in mid-June, as has been the case this year. This last occurred in 2022, the year in which the record for the highest summer temperatures is held at the buoy in the port of Valencia. On the two days before August 22, 29.72 ºC were recorded on the 9th and 29.79 ºC on the 10th of August, with minimum values not falling below 29.10 ºC.
Normally, water temperatures in mid-June are around 25 degrees Celsius.
Discrepancies and Jellyfish: The Consequences of Warming
The pronounced temperature fluctuations of the Mediterranean waters are recurring and persistent. These are episodes caused by the warming of the sea surface from the atmosphere and by the transport of warm water masses that accumulate in certain areas. To consider an episode as such, it must also exceed the threshold of high temperatures – the water must be much warmer than normal (approx. 25 ºC) and remain so for five days or longer.
“Since records began, the sea temperature has risen by more than 1.2 °C, and the years 2022 and 2023 are successively the years with the warmest water off the coast of our territory,” explained José Ángel Núñez, head of climatology at Aemet in the Valencian Community, a year ago. Thus, the average annual increase is 0.04 ºC.
Ecological Impacts: A Delicate Balance Is Tipping
Specifically, “the sea in the Balearic Islands, between the coasts of Valencia, Castelló, Tarragona, Barcelona, and Mallorca, was very warm for most of the year,” the climatologist emphasized at the time. In August 2024, the temperature averaged around 28 °C, at 27.72 °C on August 8, more than two degrees above the average sea thermometer.
The warming of the water has already led to marine imbalances. Juan Antonio Raga, professor at the University of Valencia (UV), explained to Levante-EMV last summer that “some adapt easily to changes and others find it difficult; but there are also those for whom it is impossible.” In addition, the temperature increase leads to a decrease in oxygen content in the water, “affects the calcification of corals and marine exoskeletons” and favors the development of jellyfish (both in number and size). The changes also allow exotic species to immigrate into the Mediterranean. “They reach the sea, colonize it, and displace all local species,” he adds.
