An international team of scientists reported on Friday that oceans absorbed a record amount of heat in 2025, increasing the likelihood of rising sea levels, more intense storms, and coral reef die-offs. The heat accumulated in the oceans last year reached about 23 zettajoules, equivalent to nearly four decades of the world's primary energy consumption. Researchers noted that this result, published in the journal 'Advances in Atmospheric Sciences,' is the highest annual reading since modern record-keeping began in the early 1950s. For these calculations, more than 50 scientists from 31 research institutions used multiple data sources, including a large fleet of floating robots that monitor ocean changes down to 2,000 meters. Study participant Karina von Schuckmann stated that looking into the depths of the oceans, rather than its surface fluctuations, provides a more accurate indicator of how the oceans are responding to the persistent pressure from human emissions. Oceans are a fundamental factor in regulating Earth's climate, absorbing 90% of the excess heat in the atmosphere caused by greenhouse gas emissions like carbon dioxide. This additional energy has a major impact, as rising ocean temperatures increase atmospheric humidity, providing fuel for tropical cyclones and heavy rainfall. Ocean warming directly contributes to sea-level rise, as water expands when heated, making conditions extremely difficult for tropical coral reefs, which die during prolonged marine heatwaves. Schuckmann said, 'If heat accumulation on Earth continues, ocean temperatures will keep rising, sea levels will increase, and new records will be set.' Ocean temperatures are rising faster in some regions than in others. In 2025, the oceans that absorbed record amounts of heat included the tropical oceans, the South Atlantic, the Mediterranean Sea, the North Indian Ocean, and the Southern Ocean. This was recorded despite a slight dip in the average sea surface temperature in 2025, which still remained the third-highest on record. This dip is attributed to the shift from a strong El Niño event that caused warming in 2023-2024 to conditions similar to La Niña, which is typically associated with temporary ocean surface cooling. In the long term, the rate of ocean warming is accelerating due to the continuous increase in greenhouse gas concentrations in the atmosphere, primarily from the burning of fossil fuels.
