The world’s oceans absorbed a record amount of heat in 2025, an international team of scientists said Friday, further priming conditions for sea level rise, violent storms, and coral death. The heat that has accumulated in the oceans last year increased by approximately 23 zettajoules — an amount equivalent to nearly four decades of global primary energy consumption. This finding — published in the journal Advances in Atmospheric Sciences — was the highest reading of any year since modern record keeping began in the early 1950s, researchers said.
To derive these calculations, more than 50 scientists from 31 research institutions used multiple sources including a thousands-strong fleet of floating robots that track ocean changes to depths of 2,000 metres. Peering into the depths, rather than fluctuations at the surface, provides a better indicator of how oceans are responding to “sustained pressure” from humanity’s emissions, said study co-author Karina von Schuckmann. “The picture is clear: results for 2025 confirm that the ocean continues to warm,” von Schuckmann, an oceanographer from French research institute Mercator Ocean International, told AFP.
Oceans are a key regulator of Earth’s climate because they soak up 90 percent of the excess heat in the atmosphere caused by humanity’s release of greenhouse gases like carbon dioxide. All that additional energy has a powerful knock-on effect. Warmer oceans increase moisture in the atmosphere, providing fuel for tropical cyclones and destructive rainfall.
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Hotter seas also directly contribute to sea level rise — water expands when it warms up — and make conditions unbearable for tropical reefs, whose corals perish during prolonged marine heatwaves. “As long as the Earth continues to accumulate heat, ocean heat content will keep rising, sea level will rise and new records will be set,” said von Schuckmann.
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