September the 18th, 2026 – Croatian scientists are becoming more and more concerned by Adriatic Sea test results following 75 years of frequent measurements.
Scientists from the Ruđer Bošković Institute have analysed 75 years of measurements showing that the warming and salinisation of the Mediterranean Sea are accelerating, and the changes are becoming increasingly clear even in the deep layers. The Adriatic-Ionian area stands out particularly in this regard. Morski reports that when a warmer sea in summer is discussed, it usually means the temperature that is more or less suitable for swimming near the coastline itself. However, what we see and feel near the surface is only a small part of the story. Below it lie hundreds and thousands of metres of seawater, whose deep layers change much more slowly and are considerably harder to monitor.
It was precisely in these layers of the sea that scientists from the Ruđer Bošković Institute sought an answer to the question of how much the Mediterranean has really changed over the past decades. Dr Elena Terzić and Dr Ivica Vilibić, in a paper published in the leading international geoscience journal Geophysical Research Letters, collected and connected data from different periods, from historical measurements from research vessels to modern autonomous Argo floats that today regularly dive into the depths of the sea. In this manner, they obtained a kind of cross-section of the Mediterranean from 1950 to 2025 and tracked what is happening with the temperature, salinity and density of the sea at different depths. The results show that the Mediterranean is not only warming and becoming saltier, but that the speed of these changes is increasing, and their signal can be tracked hundreds and thousands of metres below the surface.
the sea’s warmth is increasing and the process is accelerating…
We have known for a long time that the sea is warming, and this process is most often described by the average rate of warming, i.e. by how much the sea temperature increases on average over one decade. “The average rate of warming tells us how much the sea temperature changed over some longer period. However, when we describe the entire period with a single average rate, we do not see whether the speed of warming itself is also changing. Our results show that it is increasing, so the average can conceal how much faster the changes of recent decades actually are,” explains Dr Elena Terzić.
In other words, a single straight line showing average warming no longer describes well enough what is happening in the Mediterranean. That is why the scientists also analysed the acceleration of warming, i.e. whether the speed at which the temperature is rising is itself changing. The clearest signal is seen near the surface, but the more interesting part of the story begins when one looks deeper. In the last years of the analysed period the temperature in the first hundred metres or so of the Mediterranean was about two degrees higher than the average of the second half of the 20th century. Warming is clearly visible also between 300 and 1,000 metres, and a measurable signal appears even at depths between one and two kilometres.
This is important because the deep sea does not react quickly to what is happening in the atmosphere. The surface can warm up during one exceptionally hot summer and cool down again a few months later, while changes in the deep sea take place much more slowly. “When the signal of change is no longer seen only near the surface but also deep in the water column, we are talking about a much broader change in the properties of the sea. The deep layers are a kind of memory of what has been happening in the system over a longer period,” emphasises Dr Ivica Vilibić.
why does the adriatic stand out here?
The temperature is not the only thing that is changing, because the Mediterranean Sea is simultaneously becoming saltier as well, especially in its central and eastern parts. Salinity and temperature together determine the density of seawater: the higher the salinity, the denser the water, and the higher the temperature, the lower the density. It is precisely the differences in density that drive the main circulation cells in the sea, i.e. the processes by which water mixes, sinks and transfers heat and salt from one part of the Mediterranean to another. Because of this, changes that begin near the surface do not necessarily stay there.
The Adriatic has a special place in this story because it is one of the areas of the Mediterranean in which dense water is formed. During cold winter periods the surface water can cool strongly, become dense enough and begin to sink. In this way the properties that the water acquired near the surface can be transferred into the deep layers of the Adriatic, and then further towards the deep Ionian Sea and the eastern Mediterranean.
The Adriatic-Ionian system in this research proved to be one of the areas with a particularly pronounced acceleration of changes. In the southern Adriatic a strong signal of accelerated warming appears even at a depth of around 1,000 metres, accompanied by simultaneous changes in salinity. This indicates that areas in which surface water sinks can be important places for the early detection and monitoring of changes that are transferred towards the interior of the sea.
how are measurements from 1950 and 2026 connected?
One of the biggest challenges in the research was to compare the properties of the sea that over the decades were not measured in the same way. In the 1950s and 1960s the data mostly came from research vessels, while today scientists have a network of Argo floats that independently pass through the water column and regularly send data on temperature and salinity. The authors therefore combined several large data sources, checked their quality and specifically tested whether the larger number of modern measurements could introduce bias into the results, i.e. artificially create the impression of acceleration. They repeated the analyses for different time periods and with different statistical approaches, and the basic pattern remained visible.
the wider mediterranean is an early indicator
The Mediterranean is a relatively small and almost closed marine basin that reacts strongly to changes in the atmosphere. Precisely for that reason it can serve scientists as a kind of natural laboratory for understanding what is happening to the oceans in a warmer climate. The research does not give a final answer to the question of which individual process is responsible for the observed acceleration. The changes can be connected with the warming of the atmosphere, evaporation and precipitation, the exchange of water with the Atlantic through Gibraltar, and changes in the circulation of the Mediterranean itself.
For the scientists the next step is to determine the contribution of each of these processes, and what they can already conclude is that the change in the Mediterranean is no longer only a story about a warmer sea surface. The sea is changing ever faster, and the signal of these changes has reached deep below the surface.
