Ocean temperatures reached all-time high levels last year

Earth being ‘pushed beyond its limits’ as ocean temperatures reached all-time high 

Our home planet is struggling with a record energy imbalance, which is warming oceans to unprecedented levels, making weather more extreme and threatening health and food supplies, the World Meteorological Organization has warned. The UN body confirmed 2015 to 2025 were the hottest 11 years ever measured, but a still bleaker message was that the rising temperature experienced by humans on the surface was only 1% of the faster-accumulating heat in the wider Earth system. Air temperatures grab the headlines, but most of the planet’s extra heat ends up somewhere else, in the ocean. There, it can linger for decades, quietly shaping sea levels, weather extremes and marine ecosystems. State of the Climate report finds Earth’s energy has moved dangerously out of balance, with oceans absorbing vast majority of trapped heat. A new international analysis shows just how much energy the ocean is absorbing. In 2025, the world’s oceans stored more heat than in any year since modern measurements began, continuing a long-term rise which reflects how much the Earth system is still warming. Using multiple independent datasets and contributions from more than 50 scientists, the assessment estimates the ocean gained about 23 zettajoules of heat in 2025, an amount of energy comparable to decades of global human energy use. This hidden heat helps explain why seas keep rising, storms grow more intense, and climate impacts are becoming harder to ignore.

More than 90% of that excess is absorbed by the oceans, which experienced the highest heat content in history last year. The rate of ocean warming has more than doubled over the past two decades, compared with the average over the previous 45 years. Some parts of the ocean are warming faster than others, and that unevenness shapes weather patterns and marine impacts. In 2025, about 16 % of the global ocean area reached record-high heat content. About 33 % ranked among the top three warmest values in their local records. The hottest zones included the tropical and South Atlantic, the North Pacific and the Southern Ocean. The assessment also notes that ocean warming trends have been stronger since the 1990s than in earlier decades. In the upper 6,560 feet (2,000 meters), the heat increase has been steady for a while, with hints that the rate has ticked up slightly. The authors of the latest annual State of the Global Climate report say this highlights the increasing vulnerability of a planet that is moving ever further out of balance as a result of human activity. The burning of oil, gas, coal and forests releases heat-trapping greenhouse gases such as CO2, methane and nitrous oxide, which are all at their highest level in at least 800,000 years. This disrupts the planet’s energy equilibrium. In a well-functioning system, the amount of radiation entering and leaving the Earth system is roughly similar. But a heat surplus has been accumulating since at least 1960 and has noticeably accelerated in recent years.

Sea-surface temperature in 2025 ranked as the third warmest year in the instrumental record, still about 0.9 °F (0.5 °C) above the 1981–2010 average. It was slightly lower than in 2023 and 2024, largely because the tropical Pacific shifted from El Niño toward La Niña. This doesn’t contradict the ocean heat record. Surface temperatures can dip a little as heat moves around vertically and geographically, while the total heat stored in the ocean keeps climbing. Surface warmth still matters because it drives evaporation. More evaporation means more moisture in the atmosphere, which can translate into heavier rainfall and stronger tropical cyclones when storms form. The report links warm seas to major disruptions in 2025, including widespread flooding across much of Southeast Asia, drought in the Middle East and flooding in Mexico and the Pacific Northwest. This is tracked for the first time in the new report, which shows the Earth’s energy imbalance increased by about 11 zettajoules a year between 2005 and 2025, which is equivalent to about 18 times total human energy use. Last year it was more than double that average. The ocean absorbs over 90% of the excess heat trapped by greenhouse gases. This makes ocean heat content one of the most reliable ways to track long-term warming. It’s essentially the planet’s heat ledger. Air temperature can bounce around from year to year. El Niño can push it up. La Niña can pull it down. But the ocean’s heat content is less twitchy. When it rises, it signals the Earth system is still gaining heat overall.

This finding wasn’t based on one group’s numbers. The researchers combined three observational products from the Chinese Academy of Sciences, the Copernicus Marine Service, and NOAA/NCEI, along with an ocean reanalysis from CIGAR-RT, to cross-check the results. The observations all pointed the same way: 2025 hit the highest ocean heat content level on record. And it’s part of a streak, ocean has set a new record high in each of the last nine years. At present, humans and other life forms on the surface directly suffer only a small fraction of that energy backup because 91% is absorbed by oceans, 5% by the land, 1% warms the atmosphere and 3% melts ice at the poles and on high mountains. But even with only a tiny share of this extra energy, the world’s surface temperatures, which are the most commonly used measure of global heating, are climbing to alarming levels. Last year was the second- or third-hottest on record. World leaders say it is now inevitable the planet will, at least temporarily, breach the target of limiting heating to 1.5C above preindustrial levels set by the Paris agreement. They say the dire consequences are already evident in faltering harvests, worsening dengue outbreaks and increasingly severe heat waves, forest fires and storms.

Extra ocean heat has a few big downstream effects. First, it raises sea level through thermal expansion. Warmer water takes up more space, so seas rise even without adding melt water from ice. Second, it can intensify extremes. A warmer ocean can feed heat and moisture into the atmosphere, strengthening heavy rain events and helping some storms pack more punch. It can also prolong heat waves by keeping the background climate warmer. “The state of the global climate is in a state of emergency. Planet Earth is being pushed beyond its limits. Every key climate indicator is flashing red,” said the UN secretary-general, António Guterres. “Humanity has just endured the 11 hottest years on record. When history repeats itself 11 times, it is no longer a coincidence. It is a call to act.” The effect on the oceans is still not fully understood, but the impacts are expected to be still more profound and long-lasting. Sea levels are rising at an accelerating pace, and sea ice is at its third-lowest level ever. People are assembling a special collection on ocean heat content changes, including studies on regional patterns and mechanisms in places like the seas around China, the South Pacific and the Indian Ocean. The cover includes cartoon characters, a sad shrimp and a crab, suggested by the study’s corresponding author, Lijing Cheng. “The idea comes from the ‘shrimp soldiers and crab generals’ guarding the underwater palace in Journey to the West,” Cheng said. “We reimagined them not as mighty guardians, but as vulnerable creatures whose armor, their shells and scales, is under attack by ocean warming, acidification, and other ocean environmental changes.” It’s a small detail, but it captures the point. The ocean heat record isn’t just a graph. It’s pressure on ecosystems, pressure on coastlines, and fuel for the weather that hits people where they live.

The authors of the paper said more of the heat is moving into the depths, which is affecting circulation and locking in the consequences for thousands of years. Nearer the surface, heat waves and acidification are a growing problem for corals and other marine life, while the melting of ice is pushing up sea levels and weakening the planet’s ability to reflect solar radiation back into space, thus adding to the energy imbalance. The uncomfortable bottom line is straightforward: as long as the planet keeps accumulating heat, ocean heat content keeps rising. This means records will keep falling. There is no respite in sight. The Pacific is coming to the end of a La Niña phase, which is usually associated with cooler temperatures at the surface across much of the world. By the end of this year, forecasts suggest this could be replaced by an El Niño, which will bring more heating. “If we transition to El Niño we will see an increase in global temperature again and potentially to record levels,” said Dr John Kennedy.