The world’s oceans are warming at an unprecedented rate, and the changes occurring in the depths are starting to affect people everywhere. Rising sea levels, intensifying storms, and the degradation of marine ecosystems threaten coastal communities, economies, and food security, according to a new report.
Just last year, the oceans absorbed approximately 23 zettajoules of thermal energy – the equivalent of the energy released by 12 atomic bombs the size of the one in Hiroshima every second, for an entire year, writes Oceanographic Magazine.
The ocean already plays a major role in mitigating the effects of human-induced climate change, absorbing around 90% of the excess heat accumulated globally.
This warming translates into accelerated sea-level rise, changes in ocean currents and salinity, increased acidity, and storm intensification. All of these disrupt essential marine ecosystems and impact coastal communities.
"The ocean is transforming before our eyes: warming, rising sea levels, and ecosystem degradation are interconnected signs of significant and long-term change," said Pierre Bahurel, director-general of Mercator Ocean International, the organization that published the report.
The report estimates that the average sea level has risen by about 3.8 mm per year between 1999 and 2025, and between 2012 and 2025, the rate has reached 4.2 mm per year. Sea-level rise amplifies the effects of storms and extreme waves on coastal communities. In the case of small island developing states, two-thirds of their economic areas have already been directly exposed to sea-level rise since 1999.
Acidification Threatens Marine Life
The increasing absorption of carbon dioxide has led to a 17% increase in ocean acidity. Oysters, clams, sea urchins, and cold-water corals face difficulties in forming calcium carbonate structures. As these organisms decline, species higher up in the food chain, including fish important for fishing and human consumption, are also affected.
Water warming also disrupts plankton development, as it reduces the vertical mixing of the ocean and limits the supply of nutrients from the depths. Between January 2023 and September 2025, 84% of the world's coral reefs were exposed to a level of thermal stress associated with coral bleaching.
"The ocean is one of the clearest indicators of the profound changes taking place on our planet," says Celeste Saulo, Secretary-General of the World Meteorological Organization.
Arctic and Antarctica Severely Affected
In the Arctic, sea surface temperatures have risen by approximately 4.2°C in the last four decades, and the extent of sea ice has decreased by an average of about 4% per decade since the early 1980s. Ice loss also contributes to the intensification of winds and waves, accelerating coastal erosion.
In Antarctica, the reduction of sea ice already affects the fauna. In 2022, four out of five imperial penguin colonies analyzed in a region of the Bellingshausen Sea experienced complete reproductive failures due to the early loss of sea ice that chicks need until they can fly.
The report's findings come during an El Niño episode in the Pacific, which is already breaking records in certain aspects and is expected to reach maximum intensity by the end of the year. This natural warming phenomenon usually leads to further increases in ocean temperatures, beyond levels already influenced by climate change.
"The ocean is changing, and these changes are starting to affect the lives, livelihoods, and security of people everywhere. We have the knowledge. We have the evidence. Now we need the political will to act. Together, we can succeed," said Peter Thomson, the United Nations Secretary-General's Special Envoy for the Oceans. (C.S.)