The climate crisis has had enormous consequences for marine ecosystems, as demonstrated by the Copernicus Ocean State Report.
The oceans are warming ever more rapidly, the sea ice remaining at the Poles is diminishing, and marine heatwaves are becoming the norm. The latest Copernicus Ocean State Report describes a situation that is anything but normal. Yet it also tries to offer a glimmer of hope by looking to the future, because certain technologies exist that can help us, at least in part, to mitigate the impact of the climate crisis and make the oceans more resilient.
The Ocean State Report is an annual publication of the European Copernicus marine programme, produced by the research institute Mercator ocean international. In practice, it brings together the most up-to-date scientific knowledge available on the conditions of European seas and the world's oceans, with the ambition of serving as a point of reference for the scientific community, national and international bodies, policymakers, players in the so-called blue economy and the general public. The variables observed are divided into three broad categories: the physical state of the ocean (blue ocean), biogeochemical parameters (green ocean) and sea ice at the Poles (white ocean).
Greenhouse gas emissions of anthropogenic origin have interfered with the energy balance of the Earth — that is, the equilibrium between the heat radiated by the sun and that released outside the atmosphere. Through the so-called greenhouse effect, heat becomes trapped. And, of all the components of the Earth's climate system (atmosphere, hydrosphere, geosphere, cryosphere and biosphere), the oceans absorb the most. To be precise, they store almost 90 per cent of the excess heat generated by human activities.
With the relentless growth of greenhouse gas emissions, ocean warming has therefore also increased, at a rate that from the 1960s onwards stood at 0.58 watts per square metre but, from 2005, has almost doubled, reaching 1.05 watts per square metre. This increase affects every part of the world, albeit with varying intensity. It in turn has knock-on consequences for the physics of the oceans, their biogeochemical processes and marine life, as well as for the climate system as a whole.
In 1982, 50 per cent of the global ocean surface had experienced a marine heatwave. By 2023 that figure had reached 80 per cent, with 22 per cent having experienced at least one rated "severe" or "extreme". Until the mid-2000s, the regional extent and the average annual maximum duration of marine heatwaves had remained broadly stable. From 2008 onwards, both of these figures doubled — rising from 20 to 40 per cent and from 20 to 40 days respectively. In 2022, marine heatwaves affected more than two thirds of the extent of the Baltic Sea. That same year, in the Mediterranean, a marine heatwave reached a depth of 1,500 metres.
The problem is that marine heatwaves cause mass die-offs of marine organisms, force species to migrate, facilitate the spread of invasive alien species and have a devastating impact on ecosystems. In doing so, they put pressure on fisheries and hence on food security in various regions of the world. There are also areas where, as a result of these heatwaves, the layers of the ocean can no longer mix and therefore can no longer distribute nutrients optimally.
If the water is growing ever warmer, it is inevitable that sea ice will melt. The Copernicus Ocean State Report tracks its trend from 1979 to 2023, the year in which it reached its minimum extent in the polar regions. The Arctic, in particular, lost almost 2.2 million square kilometres of sea ice over those 44 years: were it a country, it would rank eleventh on the list of the world's largest. Also in 2023, the maximum extent of sea ice in Antarctica was just 16.8 million square kilometres — a figure that satellite observations had never recorded as being so low before. Compared with the average for the period 1993–2010, the loss amounts to 1.9 million square kilometres: three times the surface area of a country such as France.
In short, the human-triggered climate crisis has consequences for the oceans that are serious, tangible and plain to see. But we still have the opportunity to repair, at least in part, the damage we have caused — first and foremost by cutting greenhouse gas emissions, so as to slow the rise in the Earth's average temperature. But also by investing in technological innovation.
The Copernicus Ocean State Report cites, for example, the bay of the Estonian capital Tallinn, on the Baltic Sea, where seawater thermal energy could be used to power renewable energy production facilities. During winter, when the surface layers of the sea become too cold, slightly warmer seawater can be pumped up from the deeper layers: in this respect, cities on the Baltic Sea enjoy a favourable position.
Another of the examples cited by Copernicus concerns an entirely different territory: the port of Melilla, a Spanish autonomous city on the northern coast of Morocco. Following a violent storm that struck in 2022, researchers reconstructed changes in wave height and atmospheric patterns over the preceding three decades. They found that, between 1993 and 2022, extreme events became more intense and their return period more than halved, falling from 53 to 25 years. These are undoubtedly alarming figures. But knowing them makes it possible to work on adaptation, by modifying port infrastructure to make it more resilient and deploying early warning systems.
