Fatuma Makame learned to farm seaweed in the shallow water where her parents worked. These days, she grows it farther from shore. In the shallows, warming water has left the crop more vulnerable to poor growth and disease. While offshore environments can offer improved surroundings, operating there demands a vessel, gear, and proficiency in navigating deeper zones. Makame joined Mwani Zanzibar Mamas—a cooperative union that obtained a boat and farming gear. She has since reported larger, more reliable harvests.
That local adjustment plays out against a backdrop detailed in the 10th Copernicus Ocean State Report, released on September 30, 2026. Produced by Mercator Ocean International through the European Union’s Copernicus Marine Service and drawing on more than 40 years of data from satellites, buoys, and sensors, the assessment warns that the world’s oceans are undergoing radical transformations. According to the report, the global ocean absorbed an additional 23 zettajoules of heat in 2025—roughly equivalent to the energy of 12 Hiroshima bombs detonating every second for a year, and about 40 times the total energy consumed by the world that year.
“The ocean is transforming before our eyes: warming, rising seas and ecosystem degradation are interconnected signs of significant and long-term change. It is our responsibility to build the permanent capacity to anticipate this transformation,” said Pierre Bahurel, director-general of Mercator Ocean International.
Accelerating Sea-Level Rise and Ocean Acidification
The Copernicus assessment documents a steady acceleration in global sea levels alongside profound chemical shifts in marine environments. Global mean sea level rose by an average of 3.8 millimetres per year between 1999 and 2025, with that rate climbing to 4.2 millimetres per year from 2012 to 2025. Concurrently, the world’s oceans absorbed roughly 90 percent of the global heating produced by humans burning fossil fuels.
The report also highlights the advance of ocean acidification, which increased by approximately 17 percent between 1985 and 2025. Sometimes characterized as climate change’s equally evil twin, acidification damages delicate underwater ecosystems by making it increasingly difficult for marine organisms—including corals and lobsters—to build and maintain their shells and skeletons. On the other side of the planet, record-low Antarctic sea ice levels in 2022 coincided with the fact that climate change is shaping the habitat of ice-dependent species.
Pressures on Island Nations and Coastal Communities
The assessment examines the ocean territories of small island developing states, finding that all their exclusive economic zones have experienced ocean warming since 1960. Furthermore, about 65 percent of their combined ocean area has been exposed to accelerating sea-level rise since 1999, a figure that is 33 percent among the Indian Ocean members of that group.
Zanzibar is part of Tanzania, rather than a separate small island developing state. Throughout Unguja and Pemba, seaweed cultivation generates financial support for countless families, a significant portion of which are led or sustained by women. Growers attach young shoots to ropes, cultivate them submerged in the sea, and subsequently gather and dry the produce ready for commercial exchange. A poor harvest can leave less money for food, school fees and the next planting.
Research by the Food and Agriculture Organization outlines how elevated water temperatures can stunt seaweed development while heightening vulnerability to illnesses. Relocating cultivation zones into deeper and colder areas introduces alternative challenges: intensified currents possess the potential to ruin the harvest, while numerous producers lack swimming abilities or the apparatus required for secure offshore labor. Low prices further limit what they can spend on changing their methods.
Tanzanian marine scientist Narriman Jiddawi has documented related problems farther south, on Songo Songo Island. During an investigation ordered by the Institute of Marine Sciences, she documented excessively high water temperatures alongside pathology indicators within shallow farming locations that had been deserted. “Farming is failing in many cultivation sites in shallow intertidal areas where it used to grow well,” she said.
Karina von Schuckmann, director of the Copernicus Ocean State Report, said: “For island states, ocean change is not a distant environmental issue; it is an immediate economic, development and security challenge — and a warning of what many other coastlines will face in the future.”
For fishing families, the condition of coral reefs is one concern. Reefs provide habitat for fish and help reduce the force of waves reaching shore. Severe heat can cause corals to bleach, and repeated episodes can hinder their recovery.
