Ongoing Oceanic Heat Increase

An international team of scientists has evaluated how much heat the world's seas gain each year. In 2025, their findings reached unprecedented numbers for the eighth consecutive year, highlighting an urgent trend of rising oceanic temperatures.

Published in the journal Advances in Atmospheric Science, this study revealed that our oceans took in an extra 23 zettajoules of heat in 2025, the peak recorded since the 1960s when modern measurements began. This surpasses the 16 zettajoules of added heat recorded in 2024, with contributions from over 50 researchers worldwide.

Energy is typically quantified in joules. Though a single joule is quite minimal, sufficient only to briefly light a small bulb or slightly heat a gram of water, a zettajoule equals one sextillion joules. Consequently, the amount of heat absorbed by the oceans in 2025 can be expressed as 23,000,000,000,000,000,000,000 joules.

John Abraham, a thermal science professor at the University of St. Thomas and a contributor to the research, expresses difficulty in conveying this immense number. He often draws parallels to the power of atomic bombs, stating that the heat increase in 2025 corresponds to about 12 Hiroshima bombs detonating in the oceans. Alternatively, he equates it to the energy needed to boil 2 billion Olympic swimming pools or over 200 times the global electricity consumption.

Abraham humorously refers to the 2025 warming as 'bonkers,' underscoring the severity of the increase.

Significance of Ocean Heat Absorption

Oceans play a crucial role in absorbing over 90% of surplus thermal energy trapped in our atmosphere. While much of this heat initially heats the ocean surface, it eventually disperses to deeper levels, helped along by ocean currents and circulatory systems.

Typically, global temperature records focus on measurements from the ocean's surface. Although overall sea surface temperatures were slightly lesser in 2025 than in 2024, due in part to meteorological variations such as the transition from a strong El Niño to a weak La Niña, the broader context of rising temperatures since the industrial age cannot be ignored.

Understanding Oceanic Thermal Dynamics

Zeke Hausfather, a research scientist at Berkeley Earth and one of the study's authors, explains that surface temperatures directly affect human weather patterns and marine life. However, the heat residing in ocean depths provides critical insights into the planet’s changing climate.

According to Hausfather, oceanic heat content acts as a reliable global temperature regulator. Because the ocean captures so much heat, new records for stored ocean heat are set frequently.

The methods for calculating these figures involve an integration of sophisticated oceanic warming models and expansive data on ocean temperatures, some of which were first systematically gathered in the 1960s. The advent of the Argo float system further enhanced this, deploying over 3,500 automated buoys to collect temperature data from around the globe.

Artificial intelligence networks complemented by data from various technological sources, including satellite and underwater data-gathering from marine animals in icy waters, enhance our comprehension of ocean temperatures.

Implications and Future Concerns

UC Santa Cruz's Raphael Kudela remarks on the consistency of results across numerous datasets, which emphasize how significantly climate change is transforming our world.

He points out that it took a century to warm ocean depths to current levels, and even if fossil fuel usage ceased today, it would require centuries for this heat to redistribute fully. Thus, humanity faces long-term repercussions from the heat already packed into our oceans.