The Mediterranean Sea is becoming warmer and saltier at an accelerating rate, with the strongest changes recorded in the central and eastern Mediterranean and particularly in the Adriatic Sea, according to a new study published in Geophysical Research Letters.
Mediterranean Sea warming has already pushed temperatures in the upper 100 metres to around 2°C above the 1950–1999 average in recent years. The new research examined whether the acceleration seen at the surface is also occurring below the surface.
Researchers from Croatia’s Ruder Boskovic Institute analysed temperature and salinity measurements collected during research expeditions across the Mediterranean between 1950 and 2025.
Temperature and salinity rising
The study found that temperature and salinity are increasing across almost the entire Mediterranean, with both trends accelerating.
In some areas, temperatures are rising by up to 0.3°C per decade, while salinity is increasing by around 0.1 grams per kilogram of seawater every decade.
Researchers also observed unusually salty surface waters across parts of the Mediterranean. Conditions of this kind had historically been associated mainly with the easternmost areas of the basin.
Southern Adriatic warming faster
The most pronounced changes were recorded in the southern Adriatic. Since 2000, its deep waters have warmed around six times faster than those of a typical Mediterranean basin.
Differences in seawater density drive deep-ocean circulation. Warming makes seawater less dense, while higher salinity increases its density. Because both temperature and salinity are rising, the overall change in water density has been much smaller than the changes in either temperature or salinity alone.
Where the increase in salinity outweighs the effect of warming, water continues to sink. This process is now carrying more heat into the deeper waters of the Mediterranean.
Potential effects on oxygen and marine life
The study did not measure oxygen levels. However, warmer water can hold less oxygen, while previous observations have already recorded declining oxygen concentrations in parts of the Mediterranean.
Marine species seeking cooler conditions also have fewer potential refuges as warming reaches deeper waters.
The findings highlight the importance of looking beyond surface temperatures when assessing how climate change is affecting the Mediterranean.
Mediterranean offers wider warning
The world’s oceans have absorbed more than a quarter of human-caused carbon dioxide emissions and more than 90% of the excess heat trapped by greenhouse gases. This has helped keep the Earth’s climate milder than it otherwise would be.
The Mediterranean may provide an early indication of how quickly marine environments can respond to this additional heat.
Water in the Mediterranean circulates between the surface and deeper layers around ten times faster than in the open oceans. According to the researchers, this makes the region a useful example of how rapidly larger ocean basins could also change as global warming continues.
Also read: Heavy shipping traffic puts Mediterranean whales at risk
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