Climate change threatens the ecosystems in the Mediterranean. Warming and acidification of the water and sea level increase occur more intensively and faster than in the global average. A meta study now shows how strong the habitats in the water and on the coast of the Mediterranean are endangered with comparatively low additional warming. How much the animals, plants and people there will suffer from climate change therefore depends significantly on how much we reduce emissions from now on. The less climate protection, the warmer the Mediterranean and the greater the changes. In the worst case, entire systems would collapse.
Climate change is already clearly noticeable in the Mediterranean. There, the surface water temperature between 1982 and 2019 has already risen by 1.3 degrees and the temperatures are currently increasing to new record values: the water in front of Greece, Italy and Spain is currently up to 28 degrees Celsius. In July 2025, the water temperatures were on average at 26.9 degrees. He has been the warmest July since the beginning of the records in the Mediterranean, as the European Etreagement Service announced Copernicus. This warming endangers the habitats of plants, animals and humans – in the sea and on the coasts.
Mediterranean is a “climate change hotspot”
Researchers around Abed El Rahman Hassoun from the Geomar Helmholtz Center for Ocean Research in Kiel have now examined how climate change affects the marine and coastal ecosystems in the Mediterranean. To do this, they evaluated 131 scientific studies published by August 2023 and created risk forecasts for the further development of the Mediterranean. The course of climate change assumed in it is based on the calculated possible scenarios of the World Climate District IPCC.
The Mediterranean is an inland sea, the water masses of which are only exchanged with the global ocean. As a result, it heats up faster and more acidified; So it reacts faster and more to climate tabs than the open ocean. In this hotspot, researchers can observe the climate sequences on a relatively small area, compare with further stress factors and draw conclusions about other seas. “What happens in the Mediterranean is often a harbinger of changes that can be expected elsewhere, so that the Mediterranean looks like an early warning system for processes that will later influence the global ocean,” says Hassoun.
Additional heating by up to 3.8 degrees possible
The analysis showed: If the international climate protection goals were met in the next few years as currently planned, some environmental changes could be slowed down. With this moderate climate policy (RCP 4.5), emissions would still be released by 2040, but then decrease. In this case, between 2050 and 2100, the Mediterranean will probably heat up by 0.6 to 1.3 degrees compared to the current values. If, on the other hand, no further climate protection measures are taken and the emissions “continue as before” (RCP 8.5), the Mediterranean would heat up by a further 2.7 to 3.8 degrees in the same period.
Such warming – together with the parallel sea level increase and the ocean acidification – would significantly disrupt the ecosystems. “We have found that the ecosystems in the Mediterranean react very differently to climate-related loads. Some are more resistant than others, but none is invulnerable,” says co-author Mojahid from the University of Angers in France. Some episodes would occur with additional heating of 0.8 degrees, others only at higher values. Coral reefs and large marine animals such as whales, for example, would only damage considerable damage if heated over 3.1 degrees.
However, most other sea creatures are much more temperature sensitive: for example, toxic algae flowers and bacteria as well as invasive species would occur more frequently, sea grass meadows were lost and there would be serious chain reactions in the food networks, the team warns. The fish stocks could shrink by 30 to 40 percent and hit fishing hard. In addition, the coasts would be eroded more and rinsed the coasts and sandy beaches, dunes and rocky coasts. This would lose a habitat for animals living on the sea coast, such as turtles and birds. Plants in coastal wetlands, lagoons, deltas and salt marshes would also be affected. At the same time, there may be less rain and therefore water shortages in the Mediterranean and more frequent floods near the coast. The diverse changes would ultimately also affect the people living there.
Climate protection can limit the damage
Hassoun and his colleagues presented the results in a so-called “Burning-in-OM” diagram. This gives an overview of the existing risks for the ecosystems of the Mediterranean. “The diagram makes it clear how much climate change threatens important ecosystems. I hope that our results help to sharpen the awareness of this and to implement concrete measures to protect these unique habitats,” says Mojahid. Hassoun also hopes for stricter climate protection measures: “These scenarios show: We can still make a difference! Now it is time to act out of knowledge. Every tenth degree counts!” He says. “Political decisions that are now made decide whether the ecosystems in the Mediterranean are partially or completely collapsed or remain functional and continue to provide their ecosystem services. It is about keeping the consequences as low as possible.”
Source: Geomar Helmholtz Center for Ocean Research Kiel; Specialist articles: Scientific Reports, DOI: 10.1038/S41598-025-07858-X
