Boiling Point: The Mediterranean’s Unprecedented Heat Is a Warning We Can’t Ignore

The Mediterranean Sea is literally a climate change hotspot: it is experiencing changes in climate more rapidly and intensely than other parts of the world. This is not just in terms of warming but also changes in rainfall, leading to drier conditions that amplify the warming being experienced. Other attributes also make the Mediterranean Sea especially prone to rapid warming, it is a semi-enclosed basin meaning limited water exchange with the larger, cooler Atlantic Ocean. It’s also saltier due to high evaporation rates. More salty water absorbs and retains more heat, leading to a vicious cycle.

Broken record

While the Mediterranean Sea may be among the worst affected areas, it is by no means an isolated example. July and August of 2024 have seen searing heat for much of the globe, with temperature records continuing to be broken, despite the record heat last year. The US National Oceanic and Atmospheric Administration (NOAA) says there is now a 77% chance that 2024 will be the hottest year on record. One example of this extreme heat was evident during January to March in the Coral Sea off the East Coast of Australia, where temperatures were the warmest in 400 years, and led to the worst coral bleaching event on record for the Great Barrier Reef. Coral reefs are particularly susceptible to heat stress, and mass coral bleaching events have been reported in more than 62 countries around the world between January 2023 to May 2024.

The Mediterranean Sea also broke records this year, on 15^th August 2024 the daily median surface temperature was 28.9^oC, surpassing the record set on 24^th July 2023 when it reached 28.7^oC. Of course, medians only tell a part of the story, in the area between Nice, Corsica and the Gulf of Genoa, anomalous temperatures were a startling 5^oC warmer than average temperatures measured between 1991 and 2020.

What is sometimes missed in this story, is that the oceans significantly dampen the effects of heating on the land, having absorbed more than 90 per cent of the excess heat trapped in the atmosphere since the industrial revolution. Without the oceans, the heat would have already led to the melting of ice sheets, desertification of the soil, and loss of forests. Indeed, life on Earth would already be unsustainable.

Devastating Impact

But even the vast oceans and seas have their limits, and the impacts of this excess heat are becoming ever more apparent.

We are seeing changes in ecosystems and disruption of marine food webs. In the Mediterranean Sea, endemic Posidonia meadows, gorgonian corals and Pinna nobilis (a large species of clam) have declined throughout the region. These species provide vital habitats for many other species, and their loss leads to knock-on effects throughout the food web, which can lead to further impacts such as reduced fish catches.

The changes in temperatures have also enabled the arrival of over 1,000 invasive species into the Mediterranean Sea. These species often outcompete native species, for example, invasive rabbit fish now make up 80% of fish catches in Turkey. Other invasives, such as lionfish and pufferfish are toxic and can present dangers to people if stung, in the case of lionfish, or mistakenly eaten, in the case of pufferfish.

Research has also shown strong evidence of shifts in the distribution of some species, such as barracudas and dusky groupers that normally found in the southern Mediterranean, and which are now a common sight in the northern waters of Liguria off Italy. Of course, in a confined sea, such as the Mediterranean there are physical limits to how far these species can adapt and relocate in a response to shifting prey and warming waters.

The oceans have lost about 2% of their oxygen since the 1960s due to warming temperatures and pollution, with more and more dead zones appearing. Dead zones are areas almost devoid of marine life and tend to be coastal, where oxygen depletion is most common. In the East China Sea, the numbers of Bombay duck – actually a fish – have grown rapidly in response to low oxygen levels. While this species favours low-oxygen environments, they are outcompeting native species as these habitats become less hospitable.

Algal blooms, which can also be toxic for humans, are also becoming more common around the world. One estimate suggests that between 2003 and 2020 they became about 60 per cent common. Some of these algal species produce harmful toxins that can affect marine life. For example, an unexpected die-off of sawfish in Florida last year was eventually diagnosed as neurotoxin poisoning. The 2023 marine heatwave triggered a bloom of toxin-producing algae on the seafloor, which particularly impacted sawfish that feed on prey buried there and were consequently exposed to extremely high concentrations of toxins.

Lastly, warming waters expand. Sea level rise has doubled in the past 30 years and is expected to rise by up to one metre by 2100. This leads to coastal erosion, increased flooding risk, loss of habitat and threatens millions of people who live in low-lying coastal areas.

Can the Catastrophe Be Still Avoided?

Existing human pressures on marine life such as overfishing, trawling, pollution, coastal development, and shipping have already seriously undermined the resilience of the oceans. Climate driven impacts now threaten the foundation of our blue planet, which is essential for life on Earth.

While the recent record-breaking marine heatwaves are alarming, to many scientists they are, sadly, no surprise. The Intergovernmental Panel on Climate Change (IPCC)’s models have shown that these phenomena will become more frequent, longer lasting and more intense with global warming. Climate models also clearly show that human influence on the climate system is primarily responsible for this rapid warming in recent decades, although a warm phase in the climate cycle – called El Niño – has pushed temperatures even higher in 2023 and 2024.

Well managed marine protected areas can do a lot to reduce stress on the remaining populations as much as possible. But scientists and conservationists alike agree that immediate, rapid cuts to greenhouse gas emissions are the only real way to avoid catastrophe.

This is why we urge you, dear reader, to support out petition to end the fossil fuel era and call for a ban on oil and gas exploration.

Because our planet is blue, and needs to remain so.