The third United Nations Ocean Conference (UNOC3) provided an opportunity to discover the first annual global report on the health of the oceans. The report, which uses advanced digital modelling methods to reconstruct past trends and project future developments in ocean systems, paints an alarming picture. Each peer-reviewed finding is robustly reflected in the design of a new tool: the Starfish Barometer. This health barometer, shaped like a starfish, is more than just a snapshot of the current situation. It ranks anthropogenic pressures and highlights the interactions between these factors and marine ecosystems. This new barometer is intended to serve as a long-term indicator for monitoring the health of the ocean.
by Laurie Henry
Cover photo : Starfish barometer © M. Lévy et al., 2025
Health indicators flashing red
For the moment, data from the Starfish Barometer reveals a worrying trajectory for the ocean. Since 1901, the average sea level has risen by 23 centimetres, an acceleration attributed to global warming and thermal expansion of the waters, as well as the melting of ice caps. By 2024, it will reach a record high, increasing the vulnerability of coastal areas, where nearly 40% of the world’s population lives. Ocean temperatures are following the same trend, with 2024 exceeding the previous record by 0.25°C at the surface, illustrating an unprecedented accumulation of heat recorded over more than 64 years of measurements.
Ocean surface temperature anomalies in February 2024 compared to the 1991–2020 average. © Copernicus
Marine biodiversity is in free fall. 1,677 species are now threatened with extinction, with an alarming proportion among key predators – one third of sharks, rays and chimeras*, and 26% of cetaceans.
Coral reefs, which are home to a quarter of marine biodiversity, experienced their fourth global bleaching event in 2024. Now, 44% of reef-building coral species are at risk, and living reef cover has declined by half in a century and a half.
Anthropogenic pressures continue to grow. CO₂ emissions from fossil fuels reached 37.4 billion tonnes in 2024 (+0.8%), while those from maritime transport increased by 2.7%.
Overfishing is exacerbating the depletion of stocks: 37.7% of global fish stocks were overexploited in 2021.
Finally, plastic pollution is skyrocketing, with production reaching 413.8 million tonnes in 2023, more than 200 times the 1950 level. These plastics now account for more than 80% of aquatic debris, disrupting ecosystems down to the deepest ocean trenches.
The spiral of human and economic costs
The upheavals in the ocean are not limited to ecosystems, as they also have massive human and economic impacts. In 2023, economic losses due to tropical storms and floods reached $102 billion, a threshold that is now crossed every year. This figure represents a 25% increase per decade, a direct consequence of the intensification of extreme events linked to the warming of surface waters. With around 560 million people exposed to coastal flooding every year, the damage is no longer confined to tropical regions: coastal cities in all latitudes must strengthen their infrastructure in the face of rising sea levels and storm surges.
Indirect costs are also being felt. Marine insurance premiums jumped 5.9% in 2023 to $38.9 billion, reflecting the increase in weather-related claims, but also the worsening geopolitical tensions in maritime areas. This increase reinforces inequalities between countries, with fragile economies having less capacity to adapt to increased risks.
The human dimension of this crisis is dramatic. In 2024, 9,002 migrants died or went missing at sea, the highest toll of the decade. Scientists are warning of the growing role of environmental factors that are forcing entire populations to take to the sea in perilous conditions.
Added to this is a huge health cost. In 2015, the impact of plastic pollution on human health through seafood consumption was estimated at over $250 billion. More than 1,200 marine species are affected by plastic waste, disrupting the food chains on which millions of people depend.
Marine plastic pollution © Ahmed Areef / Alamy Stock Photo
Protection efforts still insufficient
This new barometer highlights significant but incomplete progress in ocean protection. Today, marine protected areas (MPAs) cover 8.34% of the world’s ocean surface, up from less than 1% in the 2000s. However, 25% of these MPAs are considered ‘on paper’, meaning that they exist legally but have no management or enforcement mechanisms. Only one-third of these areas have effective or high protection, while the remaining two-thirds are subject to extractive activities such as industrial fishing or mining.
The United Nations’ ambitious goal of protecting 30% of the oceans by 2030 – symbolised by the ‘30×30’ target – seems difficult to achieve without a major strengthening of political and financial commitments. Experts stress that the effectiveness of MPAs depends not only on their size, but also on their governance, the monitoring of human activities and the involvement of local communities. However, these aspects remain underdeveloped in many regions.
Pierre Bahurel points out that 88% of fishing jobs are in small-scale artisanal fisheries, which provide 25 million tonnes of food each year and support hundreds of millions of families worldwide. The lack of effective measures directly threatens this source of livelihood and increases pressure on ecosystems. While MPAs can play a key role in regenerating fish stocks and strengthening resilience to climate change, their potential is currently largely untapped.
More than just a statement of fact, the new ‘Starfish Barometer’ tool is a symbol of an international call to action. By presenting the latest data and worrying trends in an educational way, this tool invites governments, businesses and citizens to commit to reversing the trend. As Marina Lévy sums it up, ‘adopting sustainable practices is now essential to preserve the ocean, on which humanity’s survival depends’.
* Chimaeras are deep-sea cartilaginous fish, closely related to sharks and rays, with crushing tooth plates. They live in cold oceans and are vulnerable to overfishing.
Source : Lévy, M., et al., “The 2025 Starfish Barometer, in: 9th edition of the Copernicus Ocean State Report (OSR9)”. Edited by: Grégoire, M., Marcos, M., Staneva, J., Brasseur, P., Garric, G., Lionello, P., Karstensen, J., and Poulain, P.-M., Copernicus Publications, State Planet, 6-osr9, 1