The warming of the Mediterranean is accelerating the decline of biodiversity within the basin and poses risks to the health and well-being of millions of residents and visitors along its shores. Scientists watch with concern as temperatures reach levels not seen before, with the eastern region bearing the heaviest load, though the western part could follow suit, according to a report summarized in Phys.org.
From Barcelona to Tel Aviv, researchers observe dramatic rises in water temperatures, typically 3 to 5 degrees Celsius above the seasonal norm. On some days the sea surface has even topped 30 C.
The sea’s crisis goes largely unnoticed by many, yet the trend is becoming alarming. Marine heat waves arise when ocean currents transport warm patches across large areas. Like land heat waves, marine events are longer, more frequent, and more intense due to human-caused climate change.
Joaquim Garrabou of the Barcelona Institute of Marine Science notes the situation is very troubling. “We are pushing the system beyond safe limits. Climate action is urgent,” he remarks.
Garrabou’s team recently published findings on Mediterranean heatwaves from 2015 to 2019. The report highlights episodes that have caused mass die-offs among marine species along thousands of kilometers of coastline, including corals, sponges, and algae, as reported in Nature and Global Change Biology.
In the Eastern Mediterranean, the waters are at 31ºC
The eastern basin is facing especially serious conditions. Gil Rilov, a marine biologist with Israel’s Institute for Oceanographic and Limnological Studies, and one of the paper’s co-authors, calls the waters off Israel, Cyprus, Lebanon, and Syria the hottest spot in the Mediterranean. Summer averages now consistently exceed 31°C, underscoring that this is not a rare event but a new normal.
Rising temperatures are pushing many native species toward ecological limits, as optimum temperatures are surpassed each year. The team’s observations suggest that biodiversity loss will likely extend further west in coming years, affecting Greece, Italy, and Spain.
Garrabou explains that oceans absorb about 90% of excess heat and roughly 30% of carbon dioxide released from fossil fuel use. This carbon sink effect helps shield the planet from more extreme climate impacts.
However, he warns that the oceans are now in an unhealthy, destabilized state. While drastic reductions in greenhouse gas emissions are essential to curb ocean warming, oceanographers call on authorities to safeguard at least 30% of marine areas from activities such as fishing to support recovery and future development.
Current protections cover only about 8% of the Mediterranean region, and the effectiveness of those protections remains uneven. Garrabou and Rilov argue that policymakers are largely unaware of the warming and its consequences, and scientists see it as their duty to raise awareness and drive consideration of potential policy responses.
Terrestrial and marine heat waves feed off each other
Heat events tend to intensify when hot, dry conditions persist with little rainfall or wind. Terrestrial heat waves can trigger marine heat waves, creating a feedback loop that accelerates overall warming.
In many Mediterranean countries, terrestrial heat waves have become common, bringing with them wildfires, drought, crop losses, and dangerously high temperatures. If not addressed, marine heat waves could hit neighboring countries hard and affect the more than 500 million people who live around the sea. Fisheries could suffer, tourism could decline, and extreme storms may become more frequent on land as well.
Despite the Mediterranean Sea representing less than 1% of the world’s ocean surface, it hosts a significant portion of global marine biodiversity, estimated at 4% to 18% of known marine species. Key species are crucial for sustaining biodiversity and habitat health, including seagrass meadows and coral ecosystems that store carbon and support marine life. These habitats face elevated mortality risks when heat waves extend across the surface to depths of around 45 meters, with more than 90% of the sea surface affected during major events.
Rising temperatures and their implications
Recent measurements show that sea-surface temperature in the Mediterranean rose by about 0.4°C per decade from 1982 to 2018, with an acceleration of roughly 0.05°C per year over the last decade. Scientists emphasize that even small fractions of a degree can have outsized effects on ocean health. They note that affected areas have expanded since the 1980s and now cover a large portion of the basin.
Garrabou adds a stark reminder: biodiversity will persist on Earth, but human societies may struggle to live in a world where warming continues unchecked. The broader takeaway is clear: without sustained action, the Mediterranean’s ecological and socioeconomical systems face mounting pressures.
The overarching narrative aligns with careful scientific synthesis and calls for integrated management to reduce emissions while expanding protected marine spaces and strengthening resilience across coastal communities. Attribution of the discussed findings follows reports summarized in scientific outlets like Phys.org, with researchers continuing to monitor shifts in temperature, species distribution, and ecosystem health.
The situation remains urgent for governments, researchers, and local communities alike as they navigate the intertwined fate of land and sea in a warming world.