New Ocean Report Warns of Rising Seas, Ocean Heat and Acidification

Seaweed farmers tend their crop off Zanzibar, where rising sea temperatures are putting pressure on a vital coastal livelihood, according to the new Copernicus ocean report. Credit: Zuberi Mussa/IPSBy Kizito MakoyeDAR ES SALAAM, Tanzania, Sep 30 2026 (IPS) 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, warmer water has left the crop more vulnerable to poor growth and disease. Conditions can be better farther out, but working there requires a boat, equipment, and the skills to handle deeper water. Makame joined Mwani Zanzibar Mamas—a cooperative union that obtained a boat and farming gear. She has since reported larger, more reliable harvests. The decision she faced is becoming familiar to seaweed farmers along Zanzibar’s coast: move the crop, if they can afford to, or keep planting where it has become harder to grow. A new assessment of the world’s oceans gives that local difficulty a wider context. The 10th Copernicus Ocean State Report, released today (September 30), describes an ocean absorbing more heat, rising along coastlines and becoming more acidic. It was produced by Mercator Ocean International through the European Union’s Copernicus Marine Service. “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. According to the report, the global ocean absorbed an additional 23 zettajoules of heat in 2025 — roughly 40 times the energy the world consumed that year. Global mean sea level rose by an average of 3.8 millimetres a year between 1999 and 2025; the rate was 4.2 millimetres a year from 2012 to 2025. The report also says the ocean became approximately 17 percent more acidic between 1985 and 2025. Those are global measurements. They do not describe the water at Makame’s farm or explain the result of any one planting season. But Zanzibar’s seaweed farmers have had to contend with warmer water for years. Across Unguja and Pemba, seaweed provides income for thousands of households, many of them headed or supported by women. Farmers tie seedlings to lines, tend them in the water, then harvest and dry the crop for sale. A poor harvest can leave less money for food, school fees and the next planting. The Food and Agriculture Organization has documented how warmer water can inhibit seaweed growth and make it more susceptible to disease. Moving farms into deeper, cooler water presents other difficulties: stronger currents can damage the crop, and many farmers cannot swim or lack the equipment to work there safely. 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. In one study commissioned by the Institute of Marine Sciences, she recorded unusually warm water and signs of disease at shallow farming sites that had been abandoned. “Farming is failing in many cultivation sites in shallow intertidal areas where it used to grow well,” she said. Their measurements were taken at Songo Songo, not at Makame’s farm in Zanzibar. The Copernicus report also examines the ocean territories of small island developing states. It finds that all their exclusive economic zones have experienced ocean warming since 1960. About 65% of their combined ocean area has been exposed to accelerating sea-level rise since 1999. Among the Indian Ocean members of that group, the figure is 33% Zanzibar is part of Tanzania, rather than a separate small island developing state, so those percentages are not figures for the archipelago. The findings nevertheless speak to risks faced by island communities whose incomes and homes depend on the sea. “Small Island Developing States are experiencing multiple dimensions of ocean change at once. Nearly two-thirds of their ocean territories are exposed to accelerating sea-level rise, while warming seas are increasing pressure on coral reefs, fisheries and coastal communities,” said Karina von Schuckmann, director of the Copernicus Ocean State Report. “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. The report finds that about a quarter of threatened coral reefs within the ocean territories of small island developing states experienced accumulated, mortality-level heat stress for at least one month between 1982 and 2025. That is a finding for those states collectively, not an assessment of Zanzibar’s reefs. There is local evidence of damage. Researchers from the State University of Zanzibar examined reef observations spanning 1992 to 2016. They found severe declines in hard coral cover following the El Niño events of 1998 and 2016, though the extent of change differed substantially between reefs. Heat is only one of the pressures on them. Pollution and damaging fishing practices can make recovery harder. Reducing those local pressures will not cool the Indian Ocean, but it may improve the prospects for reefs that survive a period of extreme heat. Rising seas pose a separate challenge to coastal settlements. A World Bank assessment identifies Zanzibar and mainland Tanzania’s coast as vulnerable to erosion, flooding and damage to infrastructure and marine habitats. For authorities deciding where to protect homes or restrict construction, measurements of tides, storms, reefs and mangroves need to be considered alongside what residents know about places where water already reaches houses and roads. Through the Agriculture and Fisheries Development Programme, seaweed farmers in Unguja and Pemba have received training in planting, handling and processing. Improved drying racks and solar dryers help keep harvested seaweed away from sand and rain, reducing losses after it comes ashore. Other farmers are exploring additional sources of income. FAO has trained seaweed farmers on Zanzibar’s east coast in sea cucumber cultivation. That work requires suitable sites, equipment and buyers and will not suit every household. Financial protection is being explored as well. The United Nations Development Programme, Zanzibar’s disaster management authorities and the Ministry of Blue Economy and Fisheries are developing a climate-risk insurance proposal for seaweed farmers in Unguja and Pemba. It remains a proposal. Its usefulness will depend on which losses it covers, what farmers must pay, and how quickly they can settle a claim. For Makame, the cooperative’s boat and gear made it possible to try farming farther offshore. Other farmers still work the shallows. Whether they can follow her depends on access to equipment, training and a way to bear the risk if a new method fails. The Copernicus report tracks changes across decades. On Zanzibar’s coast, a farmer must decide where to put her next lines of seaweed. IPS UN Bureau Report         Related Articles Human-Caused Climate Change, Not El Niño, Drives Most Coral Bleaching Events – Research Central Asia Bets on a New Water–Land Pact to Survive Environmental Degradation Excerpt: While the 10th Copernicus Ocean State Report documents the ocean's transformation with increased heat, rising sea levels and its acidity – Zanibar's seaweed farmers feel its impact with every crop.