About 90 percent of excess heat emitted from global warming is stored in the ocean. Ocean Heat ,is therefore, a key indicator of climate change and pent up heat in the earth system. A recent study published in Advances in Atmospheric Sciences says that global ocean temperatures continued to increase in 2025.
Throughout the year, the upper 2000 m Ocean Heat levels (OHC) reached the highest value ever recorded. IAP/CAS estimates a global ocean gain of about 23ZJ of heat compared to 2024, with approximately 33 percent of the global ocean area reaching the top three warmest values in history.
Further cementing the severity of the 2025 warming signal, CIGAR-RT, NCE/NOAA and Copernicus Marine also confirmed the increases in OHC levels.The four OHC products highlight not only a new OHC record in 2025, but also sustained intensified global ocean warming.
Elevated OHC has a direct impact on the climate. It impacts the frequency and intensity of marine heatwaves, alters atmospheric circulation, increases availability of moisture and evaporation. High levels of Ocean Heat contribute to a faster sea level rise and stronger hydrological cycle. They also provide suitable conditions for intense rapid tropical cyclones.
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The Mediterranean Sea, Southern Ocean and North Atlantic recorded strong warming while warm pooling emerged in the Indo-Pacific. Cooling occurred in the tropical Atlantic, Equatorial Pacific and the Western Indian Ocean. Concurrent changes in salinity, dissolved oxygen, temperature and pH (climatic impact drivers) occurred in Mediterranean Sea and North Atlantic highlighting a significant ocean state change. These changes have a direct impact on ocean life and ecosystems.
The global SST ranked as the third-warmest year despite slight cooling of 0.08-0.12°C compared to 2024, largely due to the shift from the strong 2023–24 El Niño to La Niña conditions. Despite this cooling, it was still the third-warmest year on record, remaining well above the 1981–2010 climatological average, with cooling most evident in the tropical oceans and the midlatitude Northern Hemisphere.
Until net-zero greenhouse gas emissions are attained, the global ocean heat levels will consistently break records. Continued and accurate monitoring of the Ocean Heat levels is significant for detecting the changes and energy budget.
Strengthening ocean monitoring systems and improving our understanding of heat redistribution within the oceans are essential for producing more accurate climate assessments. It is also essential in guiding adaptation planning and supporting the development of sustainable, climate-resilient strategies.
