El The Balearic Sea has become one of the great climate change thermometers in the Mediterranean. During 2025, its waters have registered such anomalous values that scientists are already talking about an exceptional year even within a decade marked by successive records.
The data collected by the Balearic Islands Coastal Forecasting and Observation System (Socib) They show that not only have temperature marks been sprayed onto the surface, but also that The warming is spreading into increasingly deeper layersFor researchers, the situation paints a worrying picture in a basin as delicate as the western Mediterranean.
Soaring temperatures on the surface of the Balearic Sea
According to Socib records, the average surface temperatures of the Balearic Sea During 2025, they have consistently been above normal. Throughout the year, especially between winter and summer, measurements have revealed thermal anomalies of between 2 and 4 degrees with respect to the values considered normal for the region.
The situation became even more extreme in early July, when the waters reached levels that reached peaks of up to 5°C above the climate averageFrom a scientific point of view, a leap of this magnitude represents a huge change in a system as inertial as the ocean, and experts are already calling it a regional record.
These deviations were not limited to specific moments: the Balearic Sea has experienced anomalies at all stations in 2025The episodes were significant in winter and spring, but it was in summer when the situation spiraled out of control, with clear signs of a much more pronounced warming than usual.
Satellites and observation buoys confirm that June 2025 was the warmest month in the entire historical series for the area, dating back to 1982. Since satellite data has been available, such high temperatures had never been measured on the sea surface in the Balearic area at that time of year.
Alongside these average values, scientists highlight some very striking local figures: at some stations, such as the Dragonera buoy, levels reached Temperatures of 31°C were recorded on July 1stThis was an unprecedented value for the month of July in the area. A few days later, on July 7, further measurements recorded 28,5°C, an all-time high for that date and confirming the intensity of the warm spell.
Heat sinks deep: records in intermediate layers
Beyond what is happening on the surface, researchers warn of a phenomenon they consider even more disturbing: The heat content in the deep layers of the Balearic Sea has also broken records in 2025.This means that not only is the "skin" of the sea warming, but the anomaly penetrates hundreds of meters downwards.
Socib uses various platforms to monitor this process, from satellites to fixed buoys and mobile systems. Among these, the following stand out: underwater gliders and profiling buoys, which move vertically continuously measuring temperature, salinity and pressure from the surface to depths of between 150 and 700 meters.
Thanks to these tools, scientists can calculate what they call the “heat content” of the entire water columnThis is a key indicator of how much energy the sea is actually accumulating. Well, this summer's data suggests that the Balearic Islands have reached a record high in this parameter, especially in the mid-ocean layers.
The measurements show that the The warming trend is most pronounced around 500 meters deep than on the surface itself. This situation is of particular concern to specialists, since hot water, once it sinks and ceases to exchange with the atmosphere, is very difficult to cool on human timescales.
In other words, some of the excess energy being absorbed by the ocean is being “hidden” in areas where ventilation is much lower. accumulation of heat in depth It can influence both ocean dynamics and ecosystem evolution for years, even if surface temperatures drop temporarily.
Marine heat waves: more than 200 extreme days around the Balearic Islands
When ocean temperatures remain above the value that exceeds 90% of historical records for at least five days, experts speak of “marine heat waves”These are not brief episodes, but prolonged periods in which the sea remains in a state of extreme heat.
In the Balearic Islands, 2022 was already a warning: 232 days of marine heatwavesa figure that scientists considered exorbitant at the time. However, 2025 is following a very similar trajectory. By early December, approximately 210 days with marine heat waves in the archipelago area, taking the period 1982-2015 as a reference.
The researchers emphasize that the The maximum anomaly was reached precisely this year.Although 2022 remains the year with the most accumulated days of extreme heat, the level of severity reached in 2025 in the Balearic Sea is unprecedented, and there is still room for the number of extreme days to continue increasing.
In fact, during June and July, a case was recorded for the first time. Category 3 severe marine heatwave both in the Balearic Sea and the Alboran Sea. This category, the highest on the scale used to classify these phenomena, indicates an exceptionally intense and persistent heat scenario.
Scientists note that, with this episode, This marks three consecutive years of record-breaking ocean temperatures. and marine heatwaves well above normal. Based on current data, 2025 is shaping up to be another record-breaking year in the western Mediterranean and the fourth consecutive year with exceptionally anomalous ocean behavior.
The Mediterranean, a climate change hotspot
Specialists in physical oceanography insist that all this behavior is not the result of chance. The ocean functions as a huge heat reservoir And it has already absorbed more than 90% of the excess energy generated by human activities since the Industrial Revolution. This role as a buffer comes at a price: its waters are warming steadily.
The Mediterranean, and in particular the western sector where the Balearic Sea is locatedIt is considered one of the most vulnerable areas on the planet to climate change. It is a relatively small, semi-enclosed basin with limited water exchange with the Atlantic Ocean, which allows heat to accumulate more easily.
In addition to all this, the Marine heat waves often go hand in hand with atmospheric heat wavesWhen several days of very high air temperatures, clear skies and weak winds occur in succession, the sea receives a strong dose of solar radiation, loses less heat through evaporation and heats up rapidly.
This warming not only alters the physical conditions of the water, such as its density or the stability of the layers, but also It triggers a cascade of biological and chemical impacts that affect everything from microfauna and phytoplankton to large marine vertebrates.
Experts warn that, if this trend continues, Episodes of extreme heat in the Mediterranean will become more frequent, longer lasting, and more intense.What was once an exceptional event is now becoming a recurring feature of summers in the Balearic Sea and other neighboring basins.
Ecosystems in check: from Posidonia meadows to tropicalization
The ecological consequences of these record temperatures in the Balearic Sea These effects are already being felt in numerous marine habitats. Scientists describe a scenario combining mass mortalities, changes in species distribution, and the arrival of typically tropical organisms that find increasingly favorable conditions in these waters; a phenomenon that experts compare to the tropicalization of the sea.
Among the most affected ecosystems are the Posidonia oceanica meadows, a marine plant endemic to the Mediterranean that is key to the health of the sea. These meadows function like true underwater forests: they fix carbon, produce oxygen, offer refuge and breeding grounds to a multitude of species, and help stabilize sediments, protecting beaches from erosion.
The problem is that Posidonia is very sensitive to heatStudies indicate that the plant begins to suffer when the water temperature exceeds 28°C for prolonged periods. Above 30-31°C, the damage can be irreversible, with leaf loss, reduced growth, and even plant death. Given that temperatures in this range have been recorded in some parts of the Balearic Islands this summer, the concern among the scientific community is evident.
But posidonia is not the only one affected. Other effects have been observed. mortality episodes in corals, gorgonians and other sessile invertebratesThese organisms cannot quickly escape warmer areas and suffer excess mortality when marine heat waves persist. Similar cases to those described in [reference missing] have been documented in this context. corals in other regions.
Warming is also linked to an increase in harmful algal blooms and with changes in the reproductive and growth cycles of many commercial fish. Species that were once abundant may decline, while others more typical of warmer waters find a new home in the Mediterranean, a process that specialists describe as the “tropicalization” of the sea.
Less oxygen in the sea and more extreme weather events in the atmosphere
The sustained increase in temperature also has a direct effect on the dissolved oxygen in waterAs the sea warms, its capacity to store oxygen decreases, which can lead to areas with very low levels of this gas essential for marine life.
The researchers note that approximately Half of the oxygen we breathe comes from the oceanThis oxygen is largely generated by phytoplankton and other photosynthetic organisms. Although most of this oxygen does not reach the atmosphere we breathe directly, any significant alteration of the marine balance affects the stability of the global climate and biogeochemical system.
To this we must add that some Warmer waters contribute more heat and moisture to the atmosphereThis extra energy translates into additional fuel for extreme weather phenomena, such as intense storms and episodes of torrential rain, something that has already been observed repeatedly in the Mediterranean basin.
To know exactly How much energy is being stored in the intermediate and deep layers of the Balearic Sea It can improve weather and climate models. By having long series of data on the heat content in the water column, forecasting centers can refine their predictions, especially regarding high-intensity events.
In this context, observation platforms Satellites, buoys, gliders, and coastal stations have become essential tools for monitoring the evolution of the Mediterranean and anticipating possible impacts on Spanish and European coasts.
A global challenge with a direct impact on the Balearic Islands and the Western Mediterranean
The temperature records registered in the Balearic Sea during 2025 are understood as a local manifestation of a global problemOcean warming linked to greenhouse gas emissions. The scientific community insists that the only way to curb this trend is through reduce quickly and sustainably those emissions.
Experts stress the importance of protect the most fragile marine ecosystemssuch as Posidonia seagrass meadows or certain rocky seabeds that harbor high concentrations of biodiversity. In his opinion, maintaining these areas in the best possible condition helps the sea to better respond to extreme weather events.
In addition to warming, the Mediterranean is under intense pressure from the overfishing, maritime traffic, pollution and coastal urbanizationAll these factors reduce the resilience of ecosystems, that is, their ability to adapt and recover after a stressful event such as a marine heatwave.
In the Balearic Islands and the rest of the western Mediterranean, the challenge lies in combining global mitigation measures (reducing emissions and energy transition) with local actions that improve the health of the sea: creation and expansion of marine protected areas, restoration of Posidonia seagrass meadows, reduction of spills and more careful planning of activities in the coastal strip.
The succession of thermal records in the Balearic SeaThe accumulation of heat at depth and the increase in marine heatwaves are already clear signs that the Mediterranean is changing rapidly. How this challenge is addressed in the coming years will be crucial in determining the future of its ecosystems, fishing, coastal tourism, and the communities that depend directly on the health of this sea.