The Earth's oceans are undergoing disturbing changes, and scientists are warning of what is coming

The oceans are witnessing a rise in temperatures at an alarming rate, which portends dire consequences that we are not prepared to face, according to a report prepared by more than a hundred international scientists. The 10th State of the Oceans report from the European Union's Copernicus climate change monitoring service, published on Wednesday, draws on data collected over more than four decades from satellites, buoys and sensors to monitor the state of the world's oceans, issuing the "strongest warning yet" about major changes affecting these oceans.

“The ocean is changing before our eyes,” says Pierre Pahorel, director general of Mercator Ocean International, a non-profit research organization that prepared the report. “Rising temperatures, rising sea levels, and deteriorating ecosystems are all interconnected indicators of major, long-term changes.” In addition to the long-term changes observed in the report, El Niño imposes additional pressures. This natural climate phenomenon, characterized by higher than normal water temperatures along the equator in the Pacific Ocean, is on track to become the most severe in the historical record.

According to the report, the world's oceans absorb about 90% of the excess heat resulting from humans burning fossil fuels, and they are witnessing a rise in temperatures at an "alarming" pace. The pace of ocean warming has doubled over the past 20 years, with sea surface temperatures hitting record highs in 2023 and 2024 and again in 2026.

The report indicated that last year, the world's oceans absorbed an additional amount of heat equivalent to 23 zettajoules, setting a new record for the ninth year in a row. To illustrate the size of this energy, this number is equivalent to the energy of 12 atomic bombs the size of the Hiroshima bomb exploding every second over the course of an entire year, or 40 times the energy consumed by the entire world in the year 2025.

This amount of heat has widespread repercussions, potentially causing marine heatwaves, making storms more powerful and destructive, and harming marine life. It also contributes to rising sea levels, either through melting ice or as warmer water takes up more space.

Average global sea levels have risen at a rate of approximately 3.8 millimeters annually since 1999, bringing the total rise to about 101.6 millimeters, with the pace of this rise accelerating since 2012, posing a threat to hundreds of millions of people living in coastal areas. The acidity of the oceans has also increased by approximately 17% since 1985, as a result of their absorption of increasing amounts of polluting carbon emissions.

Ocean acidification harms marine ecosystems, as it hinders the ability of organisms, such as oysters, lobsters and corals, to form and maintain their exoskeletons and shells. Some regions are facing severe pressure as a result of changes associated with rising global temperatures. Karina von Schuckmann, a senior advisor at Mercator Ocean International who participated in preparing the report, noted that European seas are subject to “tremendous pressure.”

The report stated that the Mediterranean and Black Sea witnessed record marine heat waves in 2024, with some of these waves lasting for more than 30 days, leading to water temperatures rising more than 4.6 degrees Celsius above normal. In this context, Blanca Fernández-Álvarez, a researcher at the Mediterranean Institute for Advanced Studies who co-authored the report, confirms: “These are not just isolated heat waves. They are occurring in light of ongoing ocean warming that is changing the environmental conditions in which marine organisms live.”

Extreme marine phenomena have major impacts on human lives. The report cited Storm Luis, which struck the region in 2024, causing waves to rise to about 8 meters off parts of the Spanish coast, resulting in one death, a widespread power outage, and damage to infrastructure.

In the same year, another storm caused strong and continuous winds in the Gulf of Bothnia, located between Sweden and Finland. The strong winds pushed huge amounts of water out of the bay, causing a sudden and sharp drop in the water level of more than 150 centimetres, and forced ferries to stop operating for 18 hours.

Some of the biggest changes in the oceans are occurring in the rapidly warming Arctic, where sea surface temperatures have risen by about 4.2 degrees Celsius over the past four decades. Average monthly sea ice levels have fallen by 492,000 square kilometers per decade between 1979 and 2025, which equates to losing an area roughly the size of Spain every decade.

At the other end of the world, the decline of Antarctic sea ice to record levels in 2022 coincided with the first recorded case of a mass breeding failure of emperor penguins. This is "a sign that climate change is already reshaping the natural habitats of ice-dependent species," the report said.

Perhaps the countries most vulnerable to the effects of changes in the oceans are small island developing states, as these countries stand on the front lines to confront rising sea levels, the intensification of hurricanes, and the death of coral reefs. The report calls for continuous monitoring of the oceans to ensure governments and communities have the information needed to prepare for what comes next.